The verdict is still out on whether restricting salt lowers the risk of heart disease, according to a new meta-analysis by the Cochrane Collaboration.
The Cochrane reviewers pooled data from seven previous randomized controlled trials that had looked at the effects of salt (or, more precisely, sodium) reduction in 6,250 people with and without high blood pressure. Reducing sodium intake tended to lower blood pressure slightly, they found, but it had no discernible impact on lowering the rates of heart attacks, strokes or heart surgeries. Nor did it lower death rates.
In fact, the reviewers, who were led by Rod S. Taylor of the University of Exeter in Britain, found that people with congestive heart failure who restricted their sodium intake had an increased risk of death.
Further research efforts — specifically, much larger randomized controlled trials — are needed to clarify the relationship between sodium and heart disease, Taylor and his colleagues concluded.
As the review points out in its background material, most developed countries are currently trying to cut their sodium intake. The average American takes in about 3,400 milligrams (mg) of sodium daily — much more than the 2,300 mg recommended by the 2010 Dietary Guidelines for Americans. Those recommendations are even lower — no more than 1,500 mg daily — for individuals who are over the age of 50, who are black, or who have high blood pressure, diabetes or chronic kidney disease.
One teaspoon of salt contains 2,325 milligrams of sodium, but most of the sodium we consume is “hidden” in processed foods and drinks.
The U.S. Food and Drug Administration announced last year that it is developing an initiative to gradually reduce Americans’ sodium consumption. A large part of that effort will involve lowering the sodium content of processed and packaged foods.
Public health efforts to lower sodium consumption are primarily based on observational studies that have found an association between high sodium intake and an elevated risk of heart disease. But, unlike randomized controlled trials, observational studies are not designed to show a cause-and-effect relationship between two things; they can only show an association — an association that might also be explained by other factors.
That is certainly possible with the observational studies involving salt and heart disease.
“People who choose a lower salt diet are likely to also eat a diet of fresh foods, lower in fats and refined carbohydrate, take more exercise and be less likely to smoke, so that their lower levels of deaths and disease may not relate to salt intake at all,” the Cochrane reviewers point out.
The new review was published this week in the American Journal of Hypertension (AJH) as well as in the Cochrane Database of Systematic Reviews. The editor of AJH, Dr. Michael Alderman, has been an unpaid consultant to the Salt Institute in the past. The Cochrane Collaboration is an independent and international nonprofit organization.