Do You Like Your Sodium "PURE" or "Computer-Generated"?

By the very nature of science, new research and new discoveries can complicate the quest for what might be considered a definitive “truth.” This is especially important when it comes to food and nutrition, because the best scientific evidence is what is supposed to drive updating the Dietary Guidelines for Americans every five years—by extension, positively impacting our collective health and well-being.

New studies should be judged within the context of the larger body of evidence and research. It’s important to examine factors such as a study’s design, methodology, and confounding factors (variables that may or may not be accounted for), especially when the findings are novel or counterintuitive.

At that point, we then need to ask: Can the results be reproduced by other scientists?  How much elaboration or additional research is needed? Perhaps most importantly, how can we communicate findings in such a way that can help us make more informed and more healthful choices in our diets?

Bearing all of that in mind, some new research on sodium has been causing quite a stir.

The New England Journal of Medicine this week published a pair of studies that were somewhat at odds in terms of how differing levels of sodium intake are more or less likely to contribute to cardiovascular disease (CVD) or early death.

The Prospective Urban Rural Epidemiology (PURE) study of more than 100,000 people in 17 countries found that those who consumed between 3,000 mg and 6,000 mg of sodium per day had a lower risk of death and conditions like high blood pressure than those who consumed levels either above or below that range.

It’s that latter finding that is generating much of the dialogue and debate, and it’s easy to see why. Current dietary guidelines recommend no more than 2,300 mg of sodium per day among the general population and 1,500 mg among higher-risk groups. Some are advocating that the recommendation be lowered to 1,500 mg for everyone.

It should be pointed out that few of us adhere to that 2,300 mg level, to say nothing of the 1,500 mg level. In fact, just 4 percent of the study’s participants consumed sodium within the recommended range.  Americans currently consume an average of about 3,400 mg of sodium per day, calling into question whether lower levels are feasible or, in some cases, even desirable for the majority of us to achieve.

Taken in isolation, the PURE study would suggest that lowering current recommended dietary intakes for sodium isn’t supported by the science. But a major review of many other studies came to that exact conclusion.

As my colleague Kris Sollid, a registered dietitian, wrote last year, a report by the Institute of Medicine commissioned by the Centers for Disease Control and Prevention found “a positive relationship between higher levels of sodium intake and risk of CVD.”

But at the same time, the report “determined that evidence from studies on direct health outcomes is inconsistent and insufficient to conclude that lowering sodium intakes below 2,300 mg per day either increases or decreases risk of CVD outcomes (including stroke and CVD mortality) or all-cause mortality in the general U.S. population.”

The report reviewed 38 scientific studies, 34 of which were “observational,” while the remaining four were randomized control trials.

Conversely, a separate report, also published this week in the New England Journal of Medicine, used computer modeling to look at a variety of studies and suggested that 1.6 million deaths in 2010 from cardiovascular disease were attributable to sodium intake levels above 2,000 mg.

So what to make of it all?

The bottom line is that there is a strong consensus that excessively high levels of sodium intake can lead to adverse health effects. It’s just a matter of how high that level is for the general population, as well as high-risk groups, who should consume even less.

But when it comes to a lower recommended limit, how low is too low? Judging by the way some vilify salt in and of itself, it would be understandable if you thought that it was inherently bad for us. Some even go as far as to compare salt with tobacco, a notion at least one expert says is way off-base. But salt actually is critical to many vital functions in our bodies, and it has several beneficial properties for the foods we eat.

Registered dietitians at the IFIC Foundation say that some of the best advice when it comes to your health is to “know your numbers”:

First, get your blood pressure tested regularly. Normal blood pressure is less than 120/80.

Second, know your cholesterol levels, but recognize that there are both “good” (HDL) and “bad” (LDL) cholesterol. Daily HDL intake should be at least 40 mg/dL for men and 50 mg/dL for women. LDL should be 100 mg/dL or less.

And third, a critical number that most of us already know—but a lot of us would rather not think about, much less have it displayed on a tag on the back of our jeans—is our waistline. Women whose waist sizes are 35 inches or more and men whose waists are 40 inches or more are at greater risk for a variety of health problems.

As for other numbers, when it comes to salt, less is not necessarily more. Yes, Americans as a whole consume more than what is recommended. But to quote Martin O’Donnell, who authored the PURE study, in a December 2012 presentation to the Institute of Medicine (his slides are here):

“We could all use a ‘haircut’ when it comes to our sodium intake, just not a ‘buzz-cut.’”

You can find more resources on sodium and health here.