The ongoing controversy about how much salt is too much — or too little — and for which groups of people flared up again on Tuesday in a new report from the prestigious Institute of Medicine (IOM).
It appears that public-health efforts to encourage people at high risk of heart disease to consume very low levels of sodium may be increasing rather than decreasing those individuals’ health risks.
The current Dietary Guidelines for Americans recommend that most adults aged 15 to 50 consume no more than 2,300 milligrams of sodium — a key component of salt — daily to keep their hearts healthy. Those guidelines also recommend that people at high risk for heart disease — particularly those aged 51 and older, African-Americans, and people with diabetes, high blood pressure or chronic kidney disease — consume no more than 1,500 milligrams of sodium daily.
Some health organizations, most notably the American Heart Association (AHA), has argued that everybody should aim for the no-more-than-1,500-milligrams-of-sodium-daily mark.
But after studying all the research to date, the IOM’s experts determined that there’s no good evidence that cutting back on sodium to below 2,300 milligrams lowers people’s risk of heart disease.
In fact, low levels of sodium may actually have the opposite effect and increase the risk of adverse health effects in people who have been diagnosed with heart disease or who have diabetes or kidney disease.
“The evidence on both the benefit and harm is not strong enough to indicate that these subgroups should be treated differently than the general U.S. population,” the report concludes.
How much is too much?
Most Americans don’t have to worry about eating too little sodium. The average American adult consumes about 3,400 milligrams of sodium daily, or the equivalent of about 1.5 teaspoons of salt.
And the vast majority of that sodium — more than 75 percent, according to the AHA— comes hidden in processed and restaurant foods, including breads, cold cuts and processed meats, prepared chicken products, pizza, soups and sandwiches.
The IOM experts did not investigate for this report what the upper safe limit of sodium consumption should be, although they do state that “the available evidence on associations between sodium intake and direct health outcomes is consistent with population-based efforts to lower excessive dietary sodium intakes.”
But what exactly is “excessive dietary sodium intake”? And for whom?
As the IOM report notes, the current dietary guidelines for sodium consumption are based on studies that have shown that people’s blood pressure tends to fall when they eat less salt. Scientists then used that information, along with observational studies that have linked high blood pressure to an increased risk of heart disease and stroke, to estimate the number of lives that could be saved if more people consumed levels of sodium that tend not to raise blood pressure.
More recently, however, scientists haven’t been using only blood pressure as an endpoint for determining the safety of dietary sodium. They’ve also started looking at the association between levels of sodium consumption and the incidence of heart attacks and strokes. Those studies have caused some experts to question current guidelines about cutting back on sodium.
Dueling analyses
In 2011, for example, a meta-analysis by experts for the Cochrane Collaboration concluded that “cutting down on the amount of salt has no clear benefits in terms of likelihood of dying or experiencing cardiovascular disease.”
Within weeks, however, another group of researchers said their analysis of the same data found a 20 percent reduction in stroke and heart attack among people who cut back on their salt intake.
(And, yes, both the fast food and processed-food industries have a major stake in how this argument pans out, but, no, the Cochrane reviewers are not carrying water for those industries. The Cochrane Collaboration is a nonprofit and highly independent group of experts from more than 100 countries.)
Needed: better studies
The authors of the IOM report call for better research, especially more randomized controlled trials. “Such trials may be especially important among higher-risk subgroups, including African-Americans and adults 51 years of age and older,” they add, “because less rigorous observational studies in these populations may be more prone to errors and provide less robust results.”
The AHA, on the other hand, called on Tuesday for Americans to continue to aim for no more than 1,500 milligrams of sodium daily.
“While the American Heart Association commends the IOM for taking on the challenging topic of sodium consumption, we disagree with key conclusions,” said the association’s CEO Nancy Brown in a statement. “The report is missing a critical component — a comprehensive review of well-established evidence which links too much sodium to high blood pressure and heart disease.”
Stay tuned. This scientific debate is far from over.