When you think of sodium, salt probably comes to mind. Although the two terms, “sodium” and “salt” are often used interchangeably, they are different substances. The chemical name for salt, sodium chloride, reveals that sodium is in fact a component of salt. By weight, salt is composed of 40 percent sodium and 60 percent chloride. One teaspoon of salt weighs 5 grams and contains about 2,300 milligrams of sodium.
Sodium is essential for life and for good health. It is a mineral that the body cannot manufacture itself so it must be supplied by food. Sodium is readily available from various sources—foods that contain sodium naturally, foods containing salt and other sodium-containing ingredients, and from salt added to foods during cooking and at the table. As a component of salt, sodium’s most recognized role is to make foods more flavorful. Less well-known, yet important roles of sodium-containing ingredients include helping to preserve foods, improving the texture of foods, and ensuring the safety of some foods.
Compared to other minerals, the human body needs sodium in relatively large amounts. Yet, much of the world’s population consumes more than the body’s minimum requirement for sodium. In some individuals, research suggests a link between high sodium and salt intake and high blood pressure, a major risk factor for heart disease, stroke, and kidney disease. However, this relationship may be affected by concurrent intake of other key minerals, including potassium, magnesium, and calcium. Regulating sodium intake is also believed to be important in preventing and treating other health conditions.
This IFIC Review provides background on the use of sodium as a food ingredient and sodium’s role in sustaining health. It also summarizes current knowledge on the effects of sodium and salt intake on the development and treatment of disease.
HISTORY OF SALT
Salt has a long history as a highly-valued commodity. Over the years, salt has served many diverse purposes and roles beyond its use in seasoning foods. One of salt’s most recognized uses, dating back to early centuries, has been in preserving foods, including meat, fish, vegetables, and even fruit. Salting foods prevented spoiling by drawing water out of the food, depriving bacteria of the moisture needed to thrive. Without salt, the world’s food supply would have been considerably less plentiful and less safe.
Until about two hundred years ago, salting was the primary method available for preserving foods. As a result, salty flavors were common and well-accepted. By the nineteenth century, other methods of food preservation emerged, including canning, freezing, and refrigeration. This led to a change in taste preferences and a desire for less salty flavors. By the twentieth century, commercially available methods of food preservation, such as pasteurization, freeze-drying, irradiation, and the use of preservatives, allowed food manufacturers to preserve many foods on a larger scale without relying on salt. Today, salt is still used for food preservation, but the majority of the world’s salt is used for industrial purposes, including highway salting, water conditioning, and the manufacture of chlorine and other chemicals.
At various times and places throughout history, salt also played an economic role. The ancient Greeks used salt as currency. Roman soldiers received a salt ration as part of their pay, known as “salarium argentum,” from which the English word for “salary” was derived. Other cultures relied heavily on salt production and trade, and salt even has been the cause of a bitter war. Salt also has played a vital part in religious rituals in certain cultures. Over many centuries, it has been used symbolically—as a symbol of wisdom when given to a newborn in ancient Rome and, in Europe, a pinch of salt was tossed over the left shoulder three times to fend off evil. Even today, “take it with a grain of salt” is a well-known phrase that conveys the thought to not take something too seriously.
In the early 1920s, it was discovered that adding iodine to salt could prevent Iodine Deficiency Disorders (IDD), which can cause goiter and other more serious complications, including mental retardation. In the United States, salt producers made both iodized salt and plain salt available at the same cost to encourage its use. Ultimately, the widespread use of iodized salt eliminated iodine deficiency in North America. In other parts of the world, however, iodine deficiency remains a health problem because many countries lack manufacturing and packaging technologies needed to iodize salt. The elimination of iodine deficiency worldwide has been identified as one of the highest health priorities by the World Health Organization and UNICEF.
Today, salt is inexpensive and universally available. It comes from either salt mines or from the sea. Most salt is mined from large deposits left by dried salt lakes throughout the world.
SCIENCE OF SODIUM IN FOOD
Salt and other sodium-containing ingredients are commonly added during food preparation and processing. Although enhancing flavor is a key role of salt, other functional roles of sodium in food are much broader.
Taste and sensory factors
“Salty” is known as one of the five basic tastes, along with sweet, sour, bitter, and umami. Unlike the other four tastes, which have many triggers, only sodium chloride is associated with the unique taste of saltiness. Scientists have attempted to mimic this taste with salt substitutes with limited success. While lower sodium food products generally taste less salty, they often require the use of other ingredients to add or enhance flavor.
Although scientists believe that the preference for salty flavor is innate, there is evidence that the level of salt preference is learned. In fact, early experiences with low or high salt diets may have a long-term impact on an individual’s preferred salt level. [Beauchamp, 1990] Dietary exposure has been shown to influence adult salt preferences. Studies have demonstrated that a gradual reduction in sodium intake over 8 to 12 weeks can decrease preference for salty foods and increase acceptance of foods with less sodium. [Bertino et al., 1982; Mattes, 1997]
Salt serves other taste-related functions. Adding just a few grains of salt can bring out a food’s natural flavor without contributing a salty taste. Interestingly, foods with higher levels of sodium do not necessarily taste salty. For example, some baked goods may contain more sodium than some frozen entrees. Similarly, foods with surface sodium, such as French fries, typically have a greater salty taste than foods with sodium already incorporated, such as baked goods, even though they may contain less total sodium. Foods with less moisture, such as potato chips, generally require more salt for a salty taste as compared to foods with more moisture, such as French fries.
In crackers, pretzels, and other dry foods, salt is believed to decrease the perception of dryness. Salt is also used to help balance any metallic or chemical aftertaste in products such as soft drinks.
Salt is available in various crystal sizes and shapes, each with different purposes.
- Table salt is a fine-grained salt that often contains an anti-caking ingredient, such as calcium silicate, to keep it free-flowing. It is available iodized or non-iodized. This type of salt is mainly used in cooking and at the table.
- Kosher salt contains no additives and has a coarse grain. Gourmet cooks often prefer the texture and flavor of kosher salt in cooking. It is frequently used in the preparation of kosher meats.
- Sea salt comes in either fine or coarse grain and has a slightly different taste caused by other minerals it contains. It is produced by evaporation of sea water and is often named after the originating sea—Black Sea, French, or Hawaiian sea salt. Salt connoisseurs prefer sea salt for table use because they claim it has a more subtle flavor.
- Pickling salt is a fine-grained salt used for brines to make pickles and sauerkraut. It contains no iodine or anti-caking ingredients, which would make the brine cloudy.
- Specialty salts, such as popcorn salt, pretzel salt, or margarita salt, are salts of various grain sizes and textures used for special purposes. Often, other types of salt, such as table salt or kosher salt, can be substituted for these specialty salts with similar results.
- Seasoned salt is a salt blend that includes herbs and other seasoning ingredients. Because of the added flavor ingredients, this may allow for use of less seasoned salt as compared to other types of salt. This may be referred to as “light” salt for that reason.
- Salt substitutes, also referred to as light salts, typically replace all or some of the sodium with another mineral, such as potassium or magnesium.
- Rock salt is a non-food salt of a larger crystal size. Because salt lowers the freezing point of ice, it causes ice to melt. For this reason, rock salt is frequently used as a de-icing agent for sidewalks and driveways. It also is used in combination with ice to make ice cream in certain types of home ice cream freezers. As the ice melts, it absorbs heat from the ice cream, helping it to freeze more quickly.
Food preservation and safety
Salt and sodium-containing ingredients preserve the quality and safety of foods by inhibiting the growth of bacteria, yeasts, and molds, which in turn help to prevent food spoilage and foodborne illness. Foods most commonly preserved with salt and sodium-containing ingredients to prevent the growth of bacteria include cured, ready-to-eat meats and processed cheese products. Microorganisms of particular concern include Clostridium botulinum, which produces a toxin responsible for foodborne botulism, and Listeria monocytogenes, which can cause listeriosis, a serious infection with high mortality.
In ready-to-eat meats, salt, in combination with either sodium nitrate or sodium nitrite, plays an important role in preventing the growth of spoilage organisms and C. botulinum. (Jay, 2000; Doyle 1989/Hauschild) Sodium or potassium lactate and sodium diacetate in cured, ready-to-eat meat products interacts with salt to reduce or prevent Listeria growth. [Seman, 2002] In shelf-stable processed cheese products, moisture, pH, salt, and phosphate emulsifying salts all contribute to preventing the growth and toxin production by C. botulinum. (Tanaka, 1986)
Other foods also use salt as a means of preventing spoilage. For example, natural cheeses contain salt, which helps prevent growth of yeasts and molds. In salad dressings, salt along with acidic ingredients prevent the growth of spoilage bacteria, yeasts, and molds. In fermented foods, such as pickles, salt suppresses the growth of spoilage organisms while allowing the lactic acid bacteria to produce acid. The increased acidity contributes to flavor and helps limit further microbial growth. Salt is added to butter and cheese to enhance flavor and to prolong their refrigerated life.
Other functional uses of salt
Other uses of salt include as a texture aid, fermentation control, binder, and stabilizer. Adding salt to bread dough controls the fermentation action of the yeast, strengthening the gluten in bread dough to provide a uniform grain and texture. Gluten holds more water and carbon dioxide when salt is added to bread dough, allowing the dough to expand evenly without tearing. Bread made without salt will have a coarse texture and a bland flavor.
During pickling, the concentration of salt brine is gradually increased, reducing the fermentation rate. This helps to draw moisture out of foods, producing a pickled food with a crisp, firm texture.
In cured meats such as ham, salt improves tenderness by promoting the binding of water by protein. It also enables large pieces of meat to bind together so the product can be sliced. Hotdogs rely on salt for the interaction of meat proteins with fat and water. Cheese depends on salt to produce the desirable, even consistency, and the formation of a rind in certain types of cheeses.
Salt promotes the development of color in ham, bacon, and hotdogs. Used with sugar and nitrate or nitrite, salt produces an appealing color in processed meats. In baked goods, salt enhances the golden color produced when sugars are caramelized.
Adding a pinch of salt to cream or egg whites before they’re whipped helps increase the volume and serves as a stabilizer. Adding salt to water will raise the boiling point slightly. When cooking vegetables or pasta in boiling water, this enables the food to cook more quickly. A shorter cooking time allows vegetables to better retain color and nutritive value.
Functions of Common Sodium-Containing Ingredients
Sodium-containing food ingredients serve a variety of important functions.
- Sodium benzoate: a preservative that prevents growth of yeasts and bacteria; used in acidic foods such as fruit juices, jams, relishes, and beverages.
- Sodium bicarbonate (baking soda): used as a leavening agent; helps to release carbon dioxide in baked goods during baking to produce increased volume and tenderness.
- Sodium caprate (or sodium caprylate): used as a binder, emulsifier, and anti-caking agent.
- Sodium caseinate: used as a thickener and binder in coffee whiteners, nondairy whipped toppings, processed meats, and desserts.
- Sodium citrate: used in many types of foods to control acidity and stability, aid in emulsification, or improve rehydration.
- Sodium erythorbate: an antioxidant used to prevent color and flavor changes in a variety of foods.
- Sodium propionate: used as a preservative and mold inhibitor in baked goods, cheese, confections and frostings, gelatin, pudding, jams and jellies, meat products, and soft candy.
- Sodium saccharin: an artificial sweetener, also known as saccharin.
- Sodium nitrite/nitrate: a curing agent used to preserve foods and prevent growth of bacteria that cause spoilage and foodborne illness.
- Sodium sulfite (or sodium bisulfite, sodium metabisulfate): used to prevent fruit from darkening and losing flavor and vitamins while it's being dried.
- Monosodium glutamate (MSG): a flavor enhancer.
- Sodium phosphates: used as emulsifiers and stabilizers in processed cheese and to improve texture in processed meats.
- Sodium lactate and sodium diacetate: used to prevent growth of harmful bacteria, in particular Listeria monocytogenes in cured, ready-to-eat meats.
ESSENTIAL ROLE OF SODIUM IN MAINTAINING HEALTH
Sodium is an essential mineral that the body requires to maintain health. To survive, sodium must be consumed regularly in adequate amounts.
Sodium balance in the body
Sodium is a vital component of all fluids in the human body, including blood and sweat. Often working with other minerals, such as potassium and chloride, sodium’s primary role is to maintain the proper balance of fluids in the body and the acid-base balance of body fluids. Sodium and chloride mostly work outside body cells, and potassium works mainly inside cells. Together these minerals help regulate the movement of fluids in and out of body cells. This movement of fluids carries nutrients into body cells and wastes are carried out.
The kidneys regulate the body’s sodium level and the volume of water circulating in the body. In healthy individuals, excess sodium passes out through urine, and to a lesser extent, through perspiration. To counteract the effects of higher intakes of sodium, the body produces and excretes more urine. If excess sodium is not removed, such as when kidney function is impaired, swelling of body tissues may occur because sodium causes the body to retain fluid. When extra fluid is retained, blood volume increases, which in turn increases blood pressure, making the heart work harder to move blood through the blood vessels. This explains why sodium’s role in maintaining the delicate balance of fluid in the body also makes sodium a key component in regulating blood volume and pressure.
Sodium, along with chloride and potassium are referred to as electrolytes because they possess a mild electrical charge when dissolved in body fluids. With their electrical charge, sodium, chloride, and potassium help to transmit nerve impulses throughout the body. For example, the neural control of muscle contraction depends on the signals generated by these electrolytes. All three electrolytes must be in proper balance to assure normal nerve function.
Sodium deficiency is relatively uncommon. Even when sodium intake is low, the body conserves this mineral by reducing the amounted excreted through urine and sweat to maintain the balance between sodium and other fluids. However, normal healthy kidneys are not effective at conserving potassium and thus are not able to prevent a deficiency when potassium intake is low.
Chloride is also essential for good health. It helps preserve the acid-base balance in the body, aids potassium absorption, is a component of digestive stomach acid, and enhances the ability of blood to carry carbon dioxide from body tissues back to the lungs where it is exhaled from the body.
Dietary Sodium Requirements
In the Institute of Medicine’s (IOM) 2004 release of Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate, the report recommends an Adequate Intake (AI) level based on the minimum amount of sodium needed for a diet adequate in other essential nutrients and to replace sodium lost daily through perspiration for individuals engaged in recommended levels of physical activity. [DRI report]
The AI, or daily amount of sodium sufficient to meet the needs of most healthy people, is 1,500 milligrams per day (3,800 milligrams of salt) for 19- to 50-year-olds with normal blood pressure. This amount is less than half of the estimated 3,200 milligrams per day consumed on average by individuals in the United States. [NHANES III] Older adults and the elderly require somewhat less sodium based on lower energy intakes. See Table 1 for Dietary Reference Intakes for sodium for various life stage groups. Individuals engaged in higher levels of physical activity or in humid climates resulting in excessive sweating may require more than the recommended AI levels for sodium. [DRI report]
The IOM also suggests a maximum level for daily sodium consumption, known as the Tolerable Upper Intake Level (UL). For healthy individuals through the age of 50 years, the UL is 2,300 milligrams per day (5,800 milligrams of salt). The scientific report of the 2005 Dietary Guidelines Advisory Committee advises a daily sodium intake level consistent with the UL. According to this report, the general goal for adults is to reduce sodium intake to less than 2,300 milligrams of sodium per day. Older adults, African Americans, and those with chronic diseases such as hypertension, diabetes, and kidney disease are advised to reduce their intake even further. When making their recommendations, the Committee not only took into consideration sodium intake as it relates to chronic disease risk, but also current daily consumption of sodium in the United States.
Table 1: Dietary Reference Intakes for Sodium
||Adequate Intake (AI)1
|Tolerable Upper Intake Level (UL)2
|1 AIs may be used as a goal for individual intake. For healthy, breastfed infants, the AI is the mean intake. The AI
for other life stage and gender groups is believed to cover the needs of all individuals in the group, but lack of data
prevent being able to specify with confidence the percentage of individuals covered by this intake.
2 UL is the maximum level of daily intake that is likely to pose no risk of adverse effects. Unless otherwise specified,
the UL represents the total intake from food, water, and supplements.
3 ND = Not determinable due to lack of data of adverse effects in this age group and concern with regard to lack of
ability to handle excess amounts. Source of intake should be from food only to prevent high levels of intake.
|Source: Adapted from Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate.
Institute of Medicine, 2004. www.nap.edu
Effects of physical activity and temperature. Loss of sodium through increased sweating is relative to the length and level of physical activity as well as the air temperature. Individuals who exercise strenuously in the heat on a daily basis can lose significant amounts of sodium through sweat. Thus, the AI does not apply to highly active individuals, such as endurance athletes. However, the higher calorie intake required with increased physical activity is likely to provide enough sodium to meet the increased requirement. The loss of sodium through sweat is dependent on overall diet, sodium intake, sweating rate, hydration status, and degree of acclimatization to the heat. [Allsopp et al, 1998] See Sodium and Athletic Performance for additional discussion.
Effects of potassium and calcium. A high potassium intake from supplementation has been shown to increase urinary sodium excretion. [van Buren et al, 1992] Potassium is believed to inhibit sodium reabsorption in the kidneys until equilibrium is reached. Increased urinary sodium results in fluid loss and a reduction in blood volume, which is generally considered to be an important component of the blood pressure lowering effect of potassium, particularly in individuals with hypertension. Most clinical studies have used potassium supplementation to achieve the varying higher intakes of potassium. However, at least one study concluded that a sufficient increase in potassium intake (approximately 2,300 mg potassium per day) could be achieved with a potassium-based salt substitute and an increased intake of fruits and vegetables. (MacGregor et al, 1982] In view of a potential blood pressure lowering effect and reduction in the risk of kidney stones and bone loss, the Dietary Guidelines Advisory Committee Report recommends a daily potassium intake of at least 4,700 mg. [DG Report, 2004]
Higher intakes of sodium are known to result in increased urinary loss of calcium, with possible adverse effects on bone health. See the discussion of the effects of sodium on bone health. Yet effects of calcium intake on sodium excretion are not clear. Limited evidence suggests that there is little or no effect of high or low calcium diets or calcium supplementation on urinary sodium excretion. [Cappuccio et al, 1986, Weinberger et al 1993]
Effects of diuretics. Diuretics work by promoting diuresis—an increase in urine production. When the kidneys are stimulated to produce more urine, excess fluids and minerals, including sodium and chloride, are flushed from the body. The reduction in total body water helps to reduce blood volume and pressure. Diuretics may be used to treat a variety of conditions, including high blood pressure, congestive heart failure, or kidney disease. Each type of diuretic affects the body differently and can affect the balance of sodium, chloride, and potassium. When a diuretic is used to treat hypertension, a diet moderately restricted in sodium (less than 2,400 mg sodium per day) offers a balance between efficacy of the medication and safety for most individuals. [JNC, NIH, 2003] With some diuretics, potassium losses are replaced with supplements or increased intake of potassium-rich foods.
Effects of disease and body weight. In cystic fibrosis (CF), the transport of sodium and chloride between body fluids and cells is impaired, causing the production of abnormally thick and viscous mucus. As a result, the sodium and chloride content of sweat is very high. This leads to increased requirements for sodium and chloride for individuals with CF, although the exact amount is not known.
Sodium requirements also may be affected by diabetes. In situations of high blood glucose (hyperglycemia) and high levels of glucose in the urine (glycosuria), the kidneys compensate by increased excretion of water and sodium. In acute cases of hyperglycemia, blood volume and sodium levels can become severely depleted, requiring intravenous administration of water and sodium chloride, along with insulin to correct the imbalance. High blood pressure and other cardiovascular diseases are common in individuals with diabetes. These conditions often are treated with reduced sodium intake. However, some oral hypoglycemic medications, such as chlorpropramide, are associated with low blood levels of sodium caused by increased water re-absorption. [Gardenswartz and Berl, 1981]
Body weight does not appear to influence daily sodium requirements. However, a well-established relationship between body weight and hypertension indicates that weight loss reduces blood pressure. [Neter et al, 2003] One explanation for this relationship may be that overweight and obesity amplifies blood pressure response to a higher sodium intake. Thus, weight loss may help decrease blood pressure by enhancing blood pressure response to a lower sodium intake.
Effects of life stage. Limited research is available on the amount of sodium required for normal growth and development. However, growth failure has been observed in young children with salt-wasting disorders, suggesting the need for adequate sodium early in life. No studies have evaluated the effects of varying levels of sodium intake on growth in normal full-term infants. In pre-term infants, sodium appears to be necessary for normal growth. [Al-Dahhan et al, 1984] Dietary sodium is required in sufficient quantities to permit the normal expansion of blood and fluid volume that accompanies tissue growth.
Sodium requirements for infants are estimated based on the average amount of sodium in human milk and complementary foods consumed by infants at various ages. For children and adolescents, sodium recommendations, like those for adults, are based on meeting nutrient needs for other essential nutrients. The AI is thus based on the adult requirement at lower energy intake levels for children and adolescents. During pregnancy and lactation, there is a lack of evidence to suggest that sodium requirements differ from that of non-pregnant or non-lactating women. [DRI report, p6-41]
Sodium Recommendations from other Experts and Organizations
There is an ongoing dialogue on an appropriate level of daily sodium intake and the necessity of reducing sodium intake for the general population. As presented previously, the IOM and the 2005 Dietary Guidelines Advisory Committee recommendations call for a significant reduction in sodium intake for the general U.S. population. These recommendations are based on the amount of daily sodium needed to maintain health and to reduce the risk of developing hypertension. In 1994, the U.S. Food and Drug Administration established a Daily Value (DV) for sodium of 2,400 mg for use as a reference value in food labeling.
The U.S. National High Blood Pressure Education Program set a sodium intake recommendation of no more than 2,300 mg per day as a means to prevent hypertension in nonhypertensive individuals [Whelton et al, 2002] and as first line adjuvant therapy in hypertensive individuals. [NHLBI, 2003] The American Heart Association recommends no more than 2,400 mg of sodium per day for healthy Americans. In 2003, Great Britain’s Scientific Advisory Committee on Nutrition also set an upper limit of 2,400 mg of sodium per day. [British Heart Foundation, 2003]
The Canadian Hypertension Education Program urges lifestyle modifications such as exercise and weight reduction as important and actionable changes to prevent and control hypertension, but does not call for a reduction in sodium intake for individuals with normal blood pressure. [Touyz, 2004] According to a 2004 report, Canadian recommendations for the management of hypertension are to keep sodium intake at 1,500 mg to 2,300 mg per day in hypertensive individuals and less than 2,300 mg per day in normotensive individuals at high risk for developing hypertension. [Touyz, 2004] In the World Health Organization’s 2003 report, Diet, Nutrition and the Prevention of Chronic Disease, a recommendation to restrict daily sodium intake to less than 2,000 mg per day is cited in addition to an upper limit of 1,600 mg of sodium per day as a means to lower blood pressure. [WHO, 2003]
Although sodium positions vary somewhat between health and expert organizations, intake recommendations are fairly consistent. However, some guidelines also emphasize other dietary and lifestyle recommendations, in addition to reducing sodium intake, for prevention and treatment of hypertension and other health conditions.
Estimates of Actual Sodium Intake
The major form of dietary sodium is salt, which accounts for approximately 90 percent of the total sodium consumed in the United States. [Mattes and Donnelly,1991]. Other forms of sodium which contribute to the total sodium content of food include seasonings with sodium, such as monosodium glutamate, and sodium-containing ingredients, such as sodium benzoate, sodium nitrite, and sodium citrate. The primary food sources of sodium are processed and canned foods, which often contain sodium from salt or sodium-containing ingredients added during processing for flavor and a variety of other functions, such as food safety and preservation. Many condiments, including Worcestershire sauce, soy sauce, ketchup, mustard, onion salt, and bouillon cubes, also contain sodium from salt and sodium-containing ingredients.
It has been estimated that about 77 percent of the total sodium consumed by Americans is added to foods during processing, while 6 percent is added while eating, 5 percent added during cooking, and less than 1 percent is consumed from tap water. [DRI report, p6-44] Only about 12 percent of the total salt consumed is naturally occurring, coming from foods such as milk, meat, poultry, shellfish, vegetables, bottled water, and tap water. [Mattes and Donnelly, 1991]
Self-reported intake data from the Third National Health and Nutrition Examination Survey (NHANES III) indicate that the estimated median intake of sodium among adult men and women age 31 to 50 are 4,300 mg and 2,900 mg of sodium per day, respectively. Approximately 95 percent of adult men and 75 percent of adult women exceed the UL of 2,300 mg of sodium per day, and 100 percent exceed the AI of 1,500 mg of sodium per day. The self-reported sodium intakes do not include discretionary salt added at the table, thus total sodium intake is likely underestimated by NHANES III data for most individuals.
HEALTH EFFECTS OF DIETARY SODIUM
Hypertension, or high blood pressure, is identified as a major risk factor for heart disease, stroke, and kidney disease. According to recent estimates, the number of U.S. adults who have hypertension increased from about 50 million in the period from 1988 to 1994 to at least 65 million in the period from 1999 to 2000. [Fields, 2004] This equates to a prevalence rate of about 31 percent for U.S. adults.
High blood pressure is divided about equally between men and women, with about 35 million women and 30 million men suffering from the condition. African Americans tend to have the highest rate of hypertension at 39.8 percent, followed by Mexican Americans at 28.7 percent and non-Hispanic whites at 27.2 percent.
There are two forms of hypertension: essential and secondary. Most cases of high blood pressure are considered essential hypertension, which means the cause is unknown. Essential hypertension has no cure and must be treated for life. Factors thought to be linked to the development of high blood pressure include family history, advancing age, overweight, excessive alcohol intake, physical inactivity, and smoking. About 5 to 10 percent of hypertension cases are thought to result from secondary causes, such as kidney disease, thyroid disorders, pregnancy, and sleep apnea. In secondary hypertension, high blood pressure is a symptom of the underlying problem or condition, which if corrected may lower blood pressure to normal levels. Certain medications can also raise blood pressure.
Blood pressure is a measure of the force that blood exerts against blood-vessel walls as the heart muscle contracts to force blood through the arteries of the circulatory system. The first, or higher number, of a blood pressure reading is the systolic pressure—the pressure when the heart contracts; the second, or lower number, is the diastolic pressure—the pressure between heartbeats, when the heart is at rest.
The more resistance there is to a smooth blood flow, the higher the systolic and diastolic pressure. When blood volume increases or the blood vessels don’t expand enough, the flow of blood is restricted, exerting a higher force against blood vessel walls and hence a higher blood pressure. The extra pressure on blood vessels can weaken them, making them less flexible and more susceptible to hardening. As a result, blood flow to the body's organs may be slowed, leading to kidney disease, stroke, or heart attack.
In the National Heart, Lung, and Blood Institute’s (NHLBI) Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure, blood pressure is classified as normal, prehypertension, stage 1, or stage 2 based on systolic and diastolic levels. This classification is designed to aid health care providers in determining the best course of treatment (see Classification of Blood Pressure). In general, systolic pressure should be below 120 and diastolic pressure below 80. Prehypertension is considered a blood pressure range of uncertain risk, but scientists have agreed on certain cut-off points above which negative health effects are likely to result. Previously, diastolic pressure readings were considered a greater risk. In the majority of individuals with hypertension, except in those younger than age 50, elevated systolic pressure is now considered a more important risk factor for heart disease. [Alderman, 1999] However, current recommendations give equal concern to both numbers, classifying high blood pressure by either systolic or diastolic readings. For those diagnosed with hypertension (stage 1 or 2), the aim is to reduce blood pressure to at least 140/90, and to less than 130/80 for people with diabetes or chronic kidney disease. [NHLBI, 2003]
|Classification of Blood Pressure
|and < 80
Stage 1 Hypertension
Stage 2 Hypertension
|Source: The Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment
of High Blood Pressure. National Heart, Lung, and Blood Institute, May 2003.
Lifestyle management of hypertension. The exact role of lifestyle and dietary factors in the complex regulation of blood pressure is elusive because blood pressure is affected by numerous factors, including nutritional, environmental, genetic, hormonal, and metabolic factors. Treatment of hypertension involves lifestyle modifications in conjunction with medications. Lifestyle modifications are recommended by the NHLBI for individuals with prehypertension and for those with stage 1 and 2 hypertension. [NHLBI, 2003] Components of lifestyle modifications include weight reduction, the DASH eating plan (Dietary Approaches to Stop Hypertension – see inset titled “DASH Eating Plan”), dietary sodium reduction, aerobic physical activity, and moderation of alcohol consumption. Each of these lifestyle modifications have been shown to help reduce blood pressure, enhance efficacy of anti-hypertensive medications, and decrease risk for cardiovascular disease. Combinations of two or more lifestyle modifications are recommended to achieve optimal results.
Dietary management of hypertension. Several dietary factors are believed to contribute to increased blood pressure, including high sodium intake, inadequate intakes of potassium, calcium, and magnesium, high alcohol consumption, and excess body weight. Correcting these diet-related factors are key strategies in the management of high blood pressure.
According to the NHLBI, reducing dietary sodium intake from current levels to less than 2,400 milligrams per day (6 grams of salt) can result in an average systolic blood pressure reduction of 2 to 8 mmHg. [Sacks et al, 2001; Vollmer et al, 2001; Chobanian et al., 2000] In addition, adopting the DASH eating plan, which is rich in potassium, magnesium, and calcium, may further reduce systolic blood pressure by an average of 8 to 14 mmHg. [Sacks et al, 2001; Vollmer et al, 2001]
The initial DASH Trial was conducted in 1997 to study the effects of dietary patterns on blood pressure. This study compared individuals following three eating plans: a typical American diet, a plan higher in fruits and vegetables, and the DASH eating plan, which emphasized fruits, vegetables, lowfat dairy foods, whole grains, poultry, fish, nuts, and small amounts of red meat. The sodium intake of study participants remained constant at about 3,000 mg daily. Blood pressure reduction was greatest when participants followed the DASH eating plan compared to the typical American diet, especially for those with high blood pressure. [Appel et al, 1997] The results suggest that blood pressure reduction is not attributable to the influence of a single nutrient, such as sodium. Rather, blood pressure may be reduced when deficiencies of key nutrients are corrected by the DASH eating plan, namely potassium, magnesium, and calcium.
Increasing potassium intake alone has been shown to reduce salt sensitivity of blood pressure even in individuals with normal blood pressure. [Morris et al, 1999] In a study that examined the combined effects of dietary calcium, potassium, and magnesium on blood pressure, the results confirm that diets rich in these three minerals are associated with lower blood pressure levels. [Van Leer et al., 1995]
In studies of dietary potassium and calcium supplementation, salt sensitive hypertension is lowered by increased potassium and calcium intakes, which appear to increase sodium urinary excretion. [Haddy et al, 1995, Whelton et al, 1997, Allender et al.,1996] Both epidemiologic and clinical evidence suggest that dietary deficiencies of potassium or calcium potentiate the salt sensitivity of blood pressure by amplifying the effect of a high salt intake on blood pressure. [Kotchen, 1997] Study results associating magnesium with blood pressure levels are less consistent. A review of observational studies concluded that there is an inverse relationship between magnesium and blood pressure. [Mizushima et al, 1998] However, other controlled studies found no significant effect of magnesium on blood pressure. [Yamamoto et al, 1995; Sacks et al, 1998] The blood pressure-lowering effect of the DASH diet is also believed to be the result of a natural diuretic effect of fruits, vegetables, and lowfat dairy products, which stimulate to body to excrete water and sodium. [Akita et al, 2003]
The Institute of Medicine relied on various research studies to establish their current recommended daily intake of 1,500 mg sodium for the general population. The cornerstone for their report was the DASH-Sodium Trial, the largest study of the dose-response relationship between sodium intake and blood pressure. [Sacks, 2001] This feeding study was designed to test the effects on blood pressure at 3 levels of sodium intake (1,500, 2,400, and 3,300 mg per day). The varying sodium levels were combined with two distinct diets, the DASH diet and a control diet. The most notable differences in the study diets were a higher potassium, magnesium, calcium, and fiber content in the DASH eating plan.
Key findings from the DASH-Sodium Trial suggest an additive effect to blood pressure lowering in some individuals when reduced sodium intake is combined with a diet rich in potassium, calcium, and magnesium. [Sacks et al, 2001] Results showed a significant reduction in blood pressure when sodium intake was reduced to below 1,500 mg per day in both the control diet group and the DASH diet group. At each sodium level, however, the DASH diet was associated with a significantly lower systolic blood pressure compared to the control diet group. The greatest blood pressure reduction occurred in study participants following the DASH diet at the sodium intake level of 1,500 mg per day.
Numerous intervention studies have evaluated the single effect of sodium intake on blood pressure in hypertensive and non-hypertensive individuals. Relatively consistent evidence from trials of differing study populations, sizes, duration, extent of sodium reduction, background diet, and study quality suggest that a reduced sodium intake lowers blood pressure in hypertensive adults. [DRI Report, p53-55] However, some trials did not detect any lowering of blood pressure from changes in sodium intake while other trials recorded substantial reductions in blood pressure. Possible reasons for these variable results include differences in study populations, inadequate statistical power, limited differences in actual sodium intake, and other issues related to methodology.
Although the extent of blood pressure reduction in non-hypertensive individuals is less consistent, at least one review of research studies concluded that the magnitude of the reduction in blood pressure is dependant on the magnitude of the reduction in salt intake. Based on the review of 28 randomized trials, a modest reduction in salt intake to no more than 2,400 mg of sodium per day for a duration of 4 or more weeks has an important effect on blood pressure in individuals with normal and elevated blood pressure. [He & MacGregor, 2004]
DASH Eating Plan
Eating foods rich in potassium, magnesium, and calcium, as well as protein and fiber, while decreasing sodium intake has been shown to lower, and possibly prevent, high blood pressure. To follow a DASH eating plan (based on 2,000 calories a day):
- Choose foods that are low in saturated fat, cholesterol, and total fat, such as lean meats, poultry, and fish.
- Eat plenty of fruits and vegetables—aim for 8-10 servings each day. These are important sources of potassium, magnesium, and fiber.
- For calcium and protein, include 2-3 servings of low-fat or fat-free dairy foods each day.
- Reduce sodium intake to less than 2,400 mg per day by eating more fresh foods, substituting lower sodium prepared foods, and using less added salt.
- Choose whole grain foods like 100 percent whole wheat or whole grain breads and cereals.
- Eat nuts, seeds, and dry beans—4 to 5 servings per week (1 serving is 1/3 cup or 1.5 oz of nuts, 2 tbsp or ½ oz of seeds, or ½ cup cooked dry bean or peas). These foods are rich in protein and magnesium.
- Go easy on added fats, for example, choose soft margarine, low-fat mayonnaise, light salad dressing, and vegetables oils (such as olive, corn, canola, or safflower).
- Cut back on sweets and sugar-containing beverages, no more than 5 servings per week. For example, 1 serving is equal to1 tablespoon of sugar, jelly, or jam, ½ ounce of candy such as jelly beans, 8 ounces of lemonade or fruit punch).
Source: Facts About the DASH Eating Plan. U.S. Department of Health and Human Services, National Institutes of Health, National Heart, Lung, and Blood Institute, May 2003.
Primary prevention of hypertension. The “salt hypothesis” proposes that higher levels of salt in the diet lead to higher levels of blood pressure, increasing the risk of cardiovascular disease. [Intersalt, 1986] Despite evidence linking sodium reduction to lowered blood pressure in individuals with elevated blood pressure, studies exploring the effects of a reduced sodium intake as a means to prevent hypertension have found mixed results. This has fueled the debate over whether a reduced sodium intake is warranted for the general population. Experts question the magnitude and clinical significance of the fall in blood pressure caused by decreasing sodium intake in individuals with normal blood pressure.
The widespread prevalence of hypertension, which affects approximately 25 percent of the U.S. adult population, suggests that any reduction in population-wide blood pressure levels could result in substantial reductions in health care costs and reduced rates of mortality from stroke and coronary heart disease. [Whelton et al, 2002; Stamler et al, 1991] Sodium reduction is one of several nutritional therapies recommended in combination with other lifestyle intervention strategies as a means to reduce blood pressure. The National High Blood Pressure Education Program emphasizes six approaches with proven efficacy for prevention of hypertension: engage in moderate physical activity; maintain normal body weight; limit alcohol consumption; reduce sodium intake; maintain adequate intake of potassium; and consume a diet rich in fruits, vegetables, and low-fat dairy products and reduced in saturated and total fat. [Whelton, 2002] The Trial of Hypertension Phase II (TOHP2) examined the effects of sodium reduction, weight loss, or a combination of weight loss and sodium reduction in individuals with high-normal blood pressure. Findings suggested that the effects of weight loss and reduced sodium intake on blood pressure may be additive. [TOHP, 1997]
Although a relationship between lower blood pressure and reduced rates of cardiovascular disease related mortality has been established, [Domanski et al, 2002] the exact role of sodium reduction is uncertain. In fact, some studies have failed to establish a relationship between dietary sodium and mortality, with one review and analysis of 11 studies concluding that intensive interventions to significantly reduce salt intake would lead to only very small blood pressure changes in sensitive populations, such as overweight men, with no major health benefits. [Hooper et al, 2002] This study concluded that advice to reduce sodium intake may help individuals on antihypertensive drugs to stop or lower their need for medication while maintaining good control of blood pressure, but the effects of sodium reduction on overall health are unclear.
While blood pressure reduction in the DASH-Sodium Trial appeared dramatic for all study participants regardless of their blood pressure status, critics point out that the main population participating in this study was biased toward individuals with hypertension, African Americans, and those slightly overweight. Individuals with hypertension clearly experienced the greatest blood pressure reductions in this study. Health experts do agree that reducing the risk of hypertension and other cardiovascular diseases requires a comprehensive change in lifestyle for many individuals. Adherence to a combination of the DASH diet with reduced sodium intake is one tactic which may help blunt the rise in blood pressure that occurs with age. [Dietary Guidelines Advisory Committee, 2005 report] Other lifestyle changes are strongly advised, including reducing calorie intake and body weight, limiting alcohol intake, ceasing smoking, and increasing physical activity.
Individuals and their blood pressure are often labeled as “salt sensitive.” In general, salt sensitivity is a measure of how blood pressure responds to a decrease in salt intake. Individuals with the greatest reductions in blood pressure in response to decreased sodium intake are identified as salt sensitive. Because there is often considerable variance in the blood pressure response to sodium intake, both within and between individuals, presently there is no standardized definition of salt sensitivity.
According to a study supported by the NHLBI, salt sensitivity increases the risk of death whether or not a person has high blood pressure. [Weinberger et al., 2001] Researchers found that, after about 25 years, 20 percent of the study participants had died from a cardiovascular disease or other cause. Participants who had normal blood pressure, but were identified as salt sensitive at the outset, fared no better than those who were hypertensive at the outset.
There is no easy way to test for salt sensitivity, so many experts advise that all individuals with normal blood pressure follow recommendations to keep sodium intake below 2,300 milligrams per day. Individuals prone to salt sensitivity include older persons, African Americans, and those with a family member who is salt sensitive or who have a parent, sibling, or child with hypertension. One estimate suggests that about 26 percent of Americans with normal blood pressure are salt sensitive and about 58 percent of those with hypertension are salt sensitive. [Weinberger et al, 2001]
Although it has been proposed that salt sensitivity may develop as a result of a low sodium diet, this hypothesis requires further research. [Johnson et al, 2002]
High blood pressure in children and adolescents. Blood pressure among children and adolescents has increased over the past decade. Researchers believe that the small, but significant, increase in blood pressure observed in children over a 10 year period is attributed at least in part to higher rates of overweight and obesity. [Muntner et al, 2004] Other factors that may play a role include family history, sodium intake, and activity level.
Hypertension in youngsters is based on a range of blood pressures in healthy children. Normal blood pressure is defined as the systolic and diastolic blood pressures that are less than the 90th percentile for a given gender, age, and height. [NHLBI, 2004] Children with a systolic or diastolic blood pressure equal to or greater than the 90th percentile, but less than the 95th percentile are considered prehypertensive.
Treatment for children with prehypertension and high blood pressure is similar to that for adults—weight management, physical activity, and dietary changes. Drug therapy is used if needed.
Increased dietary sodium is known to trigger urinary calcium loss. With high levels of sodium intake, the body compensates by reducing reabsorption of sodium in the kidneys and increasing urinary excretion. Because sodium and calcium excretion occur together, higher levels of urinary sodium result in increased calcium excretion. [Massey and Whiting, 1996]
A study looking at the relationship between blood pressure and urinary sodium excretion with daily and fasting urinary calcium found that urinary calcium was significantly associated with blood pressure and urinary sodium. [Blackwood et al, 2001] As shown in other studies, higher intakes of sodium predicted higher calcium loss in the urine. Although this sodium-induced calcuria may be compensated by increased intestinal absorption in some individuals, such as young adults, this adaptive mechanism does not appear to function in all individuals, such as those with impaired parathyroid function, postmenopausal women with osteoporosis, and some healthy postmenopausal women.
Evidence of the long-term effects of sodium on bone health is limited. To date, long term studies have not been conducted. However, results from the DASH-Sodium Trial suggest that the DASH diet may have a beneficial effect on calcium and bone metabolism. [Doyle, 2004] Although the exact mechanism is unclear, many of the nutrients plentiful in the DASH diet, including calcium, potassium, magnesium, and vitamin C are known to have important independent roles in bone health. Other mechanisms associated with the DASH diet have been proposed, including urinary calcium retention, a lowered potential renal acid load (PRAL), and a reduction in bone turnover in response to higher potassium intake.
The DASH diet also significantly reduced markers of bone turnover. [Lin et al, 2003] When sodium was reduced from the higher to lower level in study participants consuming the DASH diet, there was a small but significant reduction in bone turnover, which suggests that reduced sodium intake may lower risk of bone fracture by conserving calcium and maximizing bone mass. The reduction in the rate of bone turnover associated with the DASH diet was found in all study participants, regardless of race, age, gender, and hypertension status. However, this finding is especially important for young adults developing peak bone mass and for older adults to slow the rate of bone loss later in life.
Kidney and Liver Diseases
As discussed previously, higher intakes of sodium can lead to increased levels of calcium in the urine. Hypercalcuria, high levels of calcium in the urine, is a common risk factor for the formation of kidney stones. In one study, individuals who formed calcium stones (calcium oxalate or calcium phosphate stones) were reported to have a higher sodium chloride intake (14 g/day) compared to healthy subjects (8 g/day). [Martini et al, 1998] In another study, relative risk of kidney stone formation was higher with an increased sodium intake. [Curhan et al, 1997] However, in a study of the role of dietary factors and risk of kidney stone formation in younger women (aged 27 to 44 years), sodium was not associated with risk for kidney stones. [Curhan, 2004] Researchers have found that individuals with a genetic predisposition to forming kidney stones have higher blood pressure and excrete more calcium in their urine. [Timio et al, 2003] In these individuals, a reduction in salt and sodium intake may be a useful method of reducing urinary calcium excretion.
A restricted intake of sodium is prescribed as part of the dietary management of acute and chronic kidney diseases. The degree of sodium restriction prescribed depends on disease severity, presence and amount of edema (abnormal swelling of body tissue due to fluid buildup), and drug therapy. The ability of the kidneys to excrete or conserve sodium is measured by changes in blood pressure, fluid status, residual renal function, and type of dialysis. In most cases, sodium intake is restricted to 2,000 to 3,000 milligrams per day to facilitate blood pressure control, maintain normal hydration status, and help prevent congestive heart failure and pulmonary edema. [ADA Manual of Clinical Dietetics, 2000]
In liver disease where edema is present, sodium restriction may be necessary to alleviate fluid retention. A restricted diet of 2,000 milligrams or less is usually sufficient.
Meniere's Disease is a condition with symptoms that include episodes of hearing loss, vertigo (dizziness), tinnitus (ringing in the ears), and a sense of pressure in the middle ear, as if descending in an airplane. The vertigo experienced in Meniere’s disease can be severe and debilitating. The cause of the disease is not known, but it is thought to be associated with the accumulation of fluid in the ears. The build-up of fluid affects the sound-sensing and balance cells in the ear. If the amount of fluid can be reduced, it may reduce the pressure and frequency of vertigo and other symptoms.
Because sodium is known to attract or hold onto fluids in the body, a low-sodium diet is often prescribed to help reduce the build up of fluid in the ear and episodes of vertigo. [Devaiah, 2000] Evidence suggests that reducing sodium to less than 1,500 milligrams per day may help some people with Meniere’s disease. However, consuming lower amounts of sodium have not been found to reduce the intensity of vertigo during episodes.
Various studies have examined the relationship between sodium intake and other health conditions, including pulmonary disease and gastric cancer. A lower sodium diet has been found to improve post-exercise pulmonary function in people with exercise-induced asthma. [Gotshall et al, 2000] Similarly, in studies where asthmatic patients were fed high salt diets, asthma symptoms worsened, suggesting that a lower sodium diet may be effective in reducing asthma symptoms. [Carey et al 1993; Medici et al, 1993]
High salt intake may be associated with increased risk of gastroesophageal reflux. A recent study of lifestyle related risk factors in the development of gastroesophageal reflux suggested a potential relationship between salt intake and reflux. [Nilsson et al, 2004] Individuals who regularly added extra salt to their meals were observed to have an increased risk of reflux symptoms. A proposed mechanism for this potential relationship was not suggested. Additional studies are needed to establish an association between salt intake and reflux.
Evidence from laboratory animal studies suggests that high intakes of salt may increase the incidence of gastric cancer. [Cohen and Roe, 1997] Researchers believe that salt may exert an enhancing effect on both the initiation and promotion steps of gastric cancer development. However, the evidence in humans is less clear. Several observational studies have confirmed a positive association between sodium or salt intake and incidence of gastric cancer, although other studies have shown no association. [DRI Report p6-95] One prospective study found that increasing salt intakes were significantly and directly associated with gastric cancer in men, but not in women. [Tsugane et al, 2004]
|Sodium and Athletic Performance
Sodium’s primary role in athletic performance is related to maintaining fluid balance. Prolonged activity and excessive sweating increases the risk of a dangerous condition known as hyponatremia, a low concentration of sodium in the blood.
During high intensity exercise and exercise in hot, humid conditions, sodium is lost along with sweat. When an athlete exercises in these conditions and only replaces the lost fluid with water, this contributes to a decreased blood sodium concentration. Athletes can lose 2 or more grams of salt per liter of sweat. For endurance athletes, who may lose a liter or more sweat per hour, this can result in a significant loss of sodium and water.
Replacing lost sodium and water is critical to performance and safety. Early warning signs of hyponatremia include nausea, muscle cramps, disorientation, slurred speech, and confusion. Left untreated, an athlete could experience seizures, coma, or death. To prevent hyponatremia, athletes should plan ahead for training and competition with these tips: [GSSI Sports Science News, 2004]
- Drink plenty of water before, during, and after exercise—enough to offset fluid loss during exercise. Thirst is considered a poor indicator of fluid needs during physical activity.
- Drink a sodium-containing sports beverage during long distance, high intensity physical activity.
- Eat salty foods before and during an event, if possible. Increasing salt intake several days prior to a competition will allow additional hydration with water to help maintain the balance of sodium and fluid. Healthy high-sodium foods include pretzels, cheese, soup, pickles.
The American College of Sports Medicine and the National Athletic Trainer’s Association advise athletes not to restrict their sodium intake. Instead, liberal salt use is recommended along with high-sodium foods and sports drinks, especially when exercising in hot conditions.
RESEARCH GAPS ON SODIUM AND HEALTH
Despite the abundance of research on sodium, well-designed studies are needed to answer these questions:
- How do sodium requirements and its health effects differ between individuals?
- What are the mechanisms involved in the dietary sodium/blood pressure relationship?
- Are there significant effects of dietary sodium, unrelated to blood pressure, on cardiovascular disease (CVD) morbidity and mortality?
- Who benefits from manipulation of dietary sodium?
- What are the practical methods for determining salt sensitivity in humans?
- Do individuals become salt-sensitive if exposed to changes in sodium intake for a sufficient period of time?
- How do other minerals interact with sodium, especially potassium, magnesium, and calcium?
- How is salt intake linked to increased risk for gastric cancer?
PRACTICAL APPLICATIONS FOR EVERYDAY PEOPLE
The level or intensity preference for salty flavors is an acquired taste. The characteristic flavor of salt is derived from the combination of sodium and chloride, not just sodium. To reduce sodium intake, experts recommend gradually cutting back on foods high in salt and sodium while using other ingredients and seasonings to enhance flavor. With a gradual decrease in salty flavors, the desire for “salty” declines and the taste buds become accustomed to less salt. [Beauchamp, 1993]
From a taste perspective, no other flavor truly substitutes for the flavor of salt. Many salt substitutes replace some or all of the sodium with potassium or magnesium. These products offer an alternative for salt, but they have been reported as having a bitter taste. For some people, especially those with kidney problems, salt substitutes with potassium are not recommended.
When watching sodium intake, the total amount of sodium consumed is most important, not necessarily the sodium content of any one food. Food labels should be used to compare and identify prepared foods that are lower in sodium, including many reduced-sodium and no-salt-added versions of prepared foods. During food preparation and at the table, reducing the amount of added salt and other sodium-containing ingredients can contribute to a lower sodium intake.
Simple strategies for reducing sodium include:
- Replace traditional higher-sodium foods with modified versions labeled as “low in sodium,” “reduced sodium,” or “lower sodium.” See Tips for Savvy Shopping inset for more tips on using food labels to evaluate the sodium content of prepared foods.
- Balance the sodium content of a favorite higher-sodium food with food choices naturally low in sodium, such as fresh foods.
- Eat smaller portions of high-sodium foods.
- Remove or decrease salt from recipes whenever possible. In most casseroles, stews, and other main dishes, you can leave out the salt. In baked goods, leaving out the salt can affect the quality and taste, but you can often reduce the amount by one-half.
- Add flavor and flair to dishes, while cooking and at the table, with herbs, spices, lemon, lime, vinegar, or salt-free seasoning blends instead of salt.
- In packaged mixes for rice, pasta, or soups, use only half of the seasoning packet and boost the flavor with other herbs and spices.
- Make your own salad dressings and sauces with lower sodium ingredients and without added salt.
- Rinse canned foods, such as vegetables or legumes, before cooking to help reduce the sodium content.
- Choose more fruits, vegetables, and milk products in forms that contain no added salt. These foods are also important sources of potassium, which can help to lower blood pressure.
- When eating out, request that salt not be added and ask for sauces and salad dressings on the side so you can control the amount you use.
- Be aware that medications can contain large amounts of sodium, such as certain antacids, laxatives, and nonsteriodal anti-inflammatory drugs. Always check the label or ask your pharmacist.
Tips for Savvy Shopping
Food labels on cans, boxes, bags and other packaging contain clues about the amount of sodium contained in one serving. You just need to know where to look.
Front of a package. Label terms may be used to call out that a product is lower in sodium. The following terms are defined by the Food and Drug Administration (FDA).
- Sodium free or salt free: Less than 5 mg per serving
- Very low sodium: 35 mg or less of sodium per serving
- Low sodium: 140 mg or less of sodium per serving
- Low sodium meal: 140 mg or less of sodium per 3 ½ oz
- Reduced or less sodium: At least 25 percent less sodium than the regular version
- Light in sodium: 50 percent less sodium than the regular version
- Unsalted or no salt added: No salt added to the product during processing
Nutrition Facts panel: Scan the amount of sodium per serving and the percent Daily Value (DV). If the amount of sodium in one serving of food contains 5 percent or less of the DV for sodium, that is considered low. If it contains 20 percent or more DV, that is considered high. The DV, a reference value on food labels established by the Food and Drug Administration, is 2,400 milligrams per day.
Ingredient list: You can determine whether a food product contains added salt and examine the types of sodium-containing ingredients included, such as monosodium glutamate, baking soda, baking powder, disodium phosphate, sodium alginate, and sodium nitrite.
Sodium is an important element in both food and health. It plays various roles in food as a component of salt and other ingredients, such as enhancing flavor of foods, assisting in food preservation and safety, and helping to improving the texture, tenderness, and stability of foods. For life and good health, sodium is an essential mineral that the body requires in adequate amounts to help balance fluids in the body, maintain blood volume and blood pressure, and assist with nerve transmission and muscle contraction. Adequate amounts of sodium are easy to obtain from food. However, most people in the U.S. and in most countries around the world consume more dietary sodium than is recommended, which may be associated with adverse health effects, especially when combined with other factors such as obesity and deficiencies of key minerals.
The study of dietary sodium and health in recent years has improved the understanding of the dietary sodium-blood pressure relationship. As a result, there is wider consensus that limiting sodium intake is beneficial for many people. Although studies investigating the effects of varying levels of sodium intake on blood pressure have produced mixed results, most health experts believe that excess sodium contributes to development of the disease in susceptible people. Additionally, reducing sodium intake as part of an overall calorie-controlled diet that is rich in potassium, calcium, and magnesium appears to be an effective dietary strategy in the treatment of high blood pressure. Further study and identification of a practical method for predicting salt sensitivity in individuals will offer more precise guidelines for modifying sodium intake.
Akita S, Sacks FM, Svetkey LP, Conlin PR, Kimura G; DASH-Sodium Trial Collaborative Research Group. Effects of the Dietary Approaches to Stop Hypertension (DASH) diet on the pressure-natriuresis relationship. Hypertension. 2003 Jul;42(1):8-13. Epub 2003 May 19.
Al-Dahhan J, Haycock GB, Chantler C, Simmler L. Sodium homeostasis in term and preterm neonates. III. Effect of salt supplementation. Arch Dis Child. 1984;59:945-50.
Alderman MH. A new model of risk: implications of increasing pulse pressure and systolic blood pressure on cardiovascular disease. J Hypertension. 1999;Suppl 5:S25-8.
Allender PS, Cutler JA, Follmann D, Cappuccio FP, Pryer J, Elliott P. Dietary calcium and blood pressure: a meta-analysis of randomized clinical trials. Ann Intern Med. 1996;124:825-829.
Allsopp AJ, Sutherland R, Wood P, Wootton SA. The effect of sodium balance on sweat sodium secretion and plasma aldosterone concentration. Eur J Applied Physiol. 1998;78:516-21.
Appel LJ, Moore TJ, Obarzanek E, Vollmer WM, Svetkey LP, Sacks FM, Bray GA, Vogt TM, Cutler JA, Windhauser MM, Lin PH, Karanja N. A clinical trial of the effects of dietary patterns on blood pressure. DASH Collaborative Research Group. N Engl J Med. 1997;336(16):1117-24.
Beauchamp GK, Cowart BJ. Preference for high salt concentrations among children. Dev Psychol. 1990;26:539-545.
Blackwood AM, Sagnella GA, Cook DG, Cappuccio FP. Urinary calcium excretion, sodium intake and blood pressure in a multi-ethnic population: results of the Wandsworth Heart and Stroke Study. J Hum Hypertens. 2001 Apr;15(4):229-37.
British Heart Foundation. Scientific Advisory Committee on Nutrition (2003) Salt and Health. London, England. www.heartstats.org. Accessed 5Nov2004.
Cappuccio FP, Markandu ND, Beynon GW, Shore AC, MacGregor GA. Effect of increasing calcium intake on urinary sodium excretion in normotensive subjects. Clin Sci. 1986;71:453-56.
Carey OJ Locke C, Cookson JB. Effect of alterations of dietary sodium on the severity of asthma in men. Thorax. 1993;48:714-718.
Chobanian AV, Hill M. National Heart, Lung, and Blood Institute Workshop on Sodium and Blood Pressure: A critical review of current scientific evidence. Hypertension. 2000;35:858-63.
Cohen JD, Granditis G, Cutler J, Neaton JD, Kuller LH, Stamler J. Dietary sodium intake and mortality: MRFIT follow up study results. Circulation. 1999;100:2758.
Curhan GC, Willett WC, Speizer FE, Spiegelman D, Stampfer MJ. Comparison of dietary calcium with supplemental calcium and other nutrients as factors affecting the risk of kidney stones in women. Ann Intern Med. 1997;126:497-504.
Curhan GC, Willett WC, Rimm EB, Stampfer MJ. Dietary factors and the risk of incident kidney stones in younger women: Nurses’ Health Study II. Arch Intern Med. 2004;164(8):885-91.
Devaiah AK, Ator GA. Clinical indicators useful in predicting response to the medical management of Meniere's disease. Laryngoscope. 2000 Nov;110(11):1861-5.
Domanski M, Mitchell G, Pfeffer M, Neaton JD, Norman J, Svendsen K, Grimm R, Cohen J, Stamler J; MRFIT Research Group. Pulse pressure and cardiovascular disease-related mortality: follow-up study of the Multiple Risk Factor Intervention Trial (MRFIT). JAMA. 2002 May 22-29;287(20):2677-83.
Doyle L. The DASH diet may have beneficial effects on bone health. Nutr Rev. 2004;62:215-20.
Fields LE, Burt VL, Cutler JA, Hughes J, Roccella EJ, Sorlie P. The burden of adult hypertension in the United States 1999 to 2000: A rising tide. Hypertension. 2004; Aug 23 epub.
Gardenswartz MH, Berl T. Drug-induced changes in water excretion. Kidney. 1981;14:19-26.
Gotshall RW, Mickleborough TD, Cordain L. Dietary salt restriction improves pulmonary function in exercise-induced asthma. Med Sci Sports Exerc. 2000;32:1815-19.
Haddy FJ, Pamnani MB. Role of dietary salt in hypertension. J Am Coll Nutr. 1995;14:428-438.
Hauschild, A, 1989. p. 125, In M. Doyle ed. Foodborne Bacterial Pathogens, Marcel Dekker, Inc. New York, NY
He F, MacGregor G. Effect of longer-term modest salt reduction on blood pressure. Cochrane Database Syst Rev. 2004;3:CD004937.
Hooper L, Bartlett C, Davey Smith G, Ebrahim S. Systematic review of long term effects of advice to reduce dietary salt in adults. BMJ. 2002 Sep 21;325:628.
Intersalt Cooperative Research Group. Intersalt study. An international co-operative study on the relation of blood pressure to electrolyte excretion in population. Design and methods. J Hypertention. 1986;4:781-7.
Institute of Medicine. Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. Standing Committee on the Scientific Evaluation of Dietary Reference Intakes, Food and Nutrition Board. 2004. National Academy Press.
Jay, J. 2000. pp. 260 – 264. In Modern Food Microbiology 6th edition. Aspen Publishers, Inc. Gaithersburg, MD.
Johnson AG, Nguyen TV, Davis D. Blood pressure is linked to salt intake and modulated by the angiotensinogen gene in normotensive and hypertensive elderly subject. J Hypertens. 2001;19:1053-60.
Johnson RJ, Herrera-Acosta J, Schreiner GF, Rodriguez-Iturbe B. Subtle acquired renal injury as a mechanism of salt-sensitive hypertension. N Engl J Med. 2002 Mar 21;346(12):913-23.
Jones DW. Dietary sodium and blood pressure. Hypertension. 2004;43:932-35.
Kenney WL. Gatorade Sports Science Institute (GSSI) Sports Science News: Dietary Fluid and Sodium Requirements for Exercising Adults. Sports Science Exchange 92, vol. 17, Number 1 2004. www.gssiweb.com.
Khaw K, Bingham S, Welch A, Luben R, O’Brien E, Wareham N, Day N. Blood pressure and urinary sodium in men and women: the Norfolk Cohort of the European Prospective Investigation into Cancer (EPIC-Norfolk). Am J Clin Nutr. 2004;80:1397-1403.
Kotchen TA, Kothen JM. Dietary sodium and blood pressure: interactions with other nutrients. Am J Clin Nutr. 1997;65(suppl):708S-11S.
Lin P, Ginty F, Appel LJ. The DASH diet and sodium reduction improve markers of bone turnover and calcium metabolism in adults. J Nutr. 2003;133:3130-36.
MacGregor GA, Markandu ND, Singer DR, Cappuccio FP, Shore AC, Sagnella GA. Moderate potassium supplementation in essential hypertension. Lancet. 1982;2:567-570.
Martini LA, Cuppar L, Cunha MA, Schor N, Heilberg IP. Potassium and sodium intake and excretion in calcium stone forming patients. J Ren Nutr. 1998;8:127-31.
Massey LK and Whiting SJ. Dietary salt, urinary calcium, and bone loss. J Bone Miner Res. 1996;11:731-6.
Mattes RD, Donnelly D. Relative contributions of dietary sodium sources. J Am Coll Nutr. 1991;10:383-93.
Mattes RD. The taste for salt in humans. Am J Clin Nutr. 1997;65(suppl):692S-697S.
Medici TC, Schmid AZ, Hacki M, Vetter W. Are asthmatics salt-sensitive? A preliminary controlled study. Chest. 1993;104:1138-43.
Mitka M. Dash of dissent on salt intake advice. JAMA. 2004:291:1686-1689.
Mizushima S, Cappuccio FP, Nichols R, Elliott P. Dietary magnesium intake and blood pressure: a qualitative overview of the observational studies. J Hum Hypertens. 1998;12:447-453.
Morris RC Jr, Sebastian A, Forman A, Tanaka M, Schmidlin O. Normotensive salt sensitivity: Effects of race and dietary potassium. Hypertension. 1999;33:18-23.
Muntner P, He J, Cutler JA, Wildman RP, Whelton PK. Trends in blood pressure among children and adolescents. JAMA. 2004;291:2107-13.
National Heart, Lung, and Blood Institute; National High Blood Pressure Education Program Coordinating Committee. The Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC 7). Hypertension. 2003 Dec;42(6):1206-52.
National High Blood Pressure Education Program Working Group on High Blood Pressure in Children and Adolescents. The Fourth Report on the Diagnosis, Evaluation, And Treatment of High Blood Pressure in Children and Adolescents. Pediatrics. 2004 Aug;114(2 Suppl 4th Report):555-76.
Neter JE, Stam BE, Kok FJ, Grobbee DE, Geleijnse JM. Influence of weight reduction on blood pressure: a meta-analysis of randomized controlled trials. Hypertension. 2003;42:878-884.
Nilsson M, Johnsen R, Ye W, Hveem K, Lagergren J. Lifestyle related risk factors in the aetiology of gastro-oesophageal reflux. Gut. 2004;53(12):1730-5.
Sacks FM, Willett WC, Smith A, Brown LE, Rosner B, Moore TJ. Effect of blood pressure of potassium, calcium, and magnesium in women with low habitual intake. Hypertension. 1998;31(pt 1):131-138.
Sacks FM, Svetkey LP, Vollmer WM, et al. Effects on blood pressure of reduced dietary sodium and the Dietary Approaches to Stop Hypertension (DASH) diet. DASH-Sodium Collaborative Research Group. N Engl J Med. 2001;344:3-10.
Seman DL, Borger AC, Meyer JD, Hall PA, Milkowski AL. Modeling the growth of Listeria monocytogenes in cured ready-to-eat processed meat products by manipulation of sodium chloride, sodium diacetate, potassium lactate, and product moisture content. J Food Prot. 2002;65(4):651-8.
Stamler J, Rose G, Elliott P, Dyer A, Marmot M, Kesteloot H, Stamler R. Findings of the international cooperative INTERSALT study. Hypertension. 1991;17:I9S-I15S.
Tanaka, N., E. Traisman, P. Plantinga, L. Finn, W. Flom, L. Meske, and J. Guggisberg. 1986. Evaluation of factors involved in antibotulinal properties of pasteurized process cheese spreads. J. Food Protection. 49 (7):526-531.
Timio F, Kerry SM, Anson KM, Eastwood JB, Cappuccio FP. Calcium urolithiasis, blood pressure and salt intake. Blood Press. 2003;12(2):122-7.
TOHP (Trials of Hypertension Prevention) Collaborative Research Group. Effects of weight loss and sodium intervention on blood pressure and hypertension incidence in overweight people with high-normal blood pressure. The Trials of Hypertension Prevention, Phase II. Arch Intern Med. 1997;157:657-667.
Touyz RM, Campbell N, Logan A, Gledhill N, Petrella R, Padwal R; Canadian Hypertension Education Program. The 2004 Canadian recommendations for the management of hypertension: Part III--Lifestyle modifications to prevent and control hypertension. Can J Cardiol. 2004 Jan;20(1):55-9.
Tsugane S, Sasazuki S, Kobayashi M, Sasaki S. Salt and salted food intake and subsequent risk of gastric cancer among middle-aged Japanese men and women. Br J Cancer. 2004;90:128-134.
van Buren M, Rabelink TJ, van Rijn HJ, Koomans HA. Effects of acute NaCl, KCl and KHCO3 loads on renal electrolyte excretion in humans. Clin Sci. 1992;83:567-74.
Van Leer EM, Seidell JC, Kromhout. Dietary calcium, potassium, magnesium and blood pressure in the Netherlands. Int J Epidemiol. 1995;24:1117-1123.
Vollmer WM, Sacks FM, Ard J, et al. Effects of diet and sodium intake on blood pressure: Subgroup analysis of the DASH-sodium trial. Ann Intern Med. 2001;135:1019-28.
Weinberger MH, Wagner UL, Fineberg NS. The blood pressure effects of calcium supplementation in humans of known sodium responsiveness. Am J Hypertens. 1993;6:799-805.
Weinberger MH, Fineberg NS, Fineberg SE, Weinberger M. Salt sensitivity, pulse pressure, and death in normal and hypertensive humans. Hypertension. 2001 Feb;37(2 Part 2):429-32.
Whelton PK, He J, Cutler JA, Brancati FL, Appel LJ, Follmann D, Klag MJ. Effects of oral potassium on blood pressure: meta-analysis of randomized clinical trials. JAMA. 1997;277:1624-1632.
Whelton PK, He J, Appel LJ, Cutler JA, Havas S, Kotchen TA, Roccella EJ, Stout R, Vallbona C, Winston MC, Karimbaka J. Primary prevention of hypertension: Clinical and public health advisory from the National High Blood Pressure Education Program. JAMA. 2002;288:1882-8.
Joint WHO/FAO Expert Consultation on Diet, Nutrition and the Prevention of Chronic Diseases. Diet, Nutrition and the Prevention of Chronic Diseases. Geneva, Switzerland, 2003. http://www.who.int/hpr/NPH/docs/who_fao_expert_report.pdf. Accessed December 20, 2004.
Yamamoto ME, Applegate WB, Klag MJ, Borhani NO, Cohen JD, Kirchner KA, Lakatos, E, Sacks FM, Taylor JO, Hennekens CH. Lack of blood pressure effect with calcium and magnesium supplementation in adults with high-normal blood pressure: results from Phase I of the Trials of Hypertension Prevention (TOPH). Ann Epidemiol. 1995;5:96-107.