Statement on New Studies of Salt and Cardiovascular Disease
Statement of CSPI Nutrition Director Bonnie F. Liebman
August 13, 2014
The results of the PURE studies (by O’Donnell et al. and Mente et al.) should not change advice by health authorities—American Heart Association, Centers for Disease Control and Prevention, and others—to consume less salt to reduce the risk of cardiovascular disease.
The PURE studies suffer from serious shortcomings. First, the O’Donnell study might have found a higher risk of cardiovascular events and death among those consuming the least salt because some of those subjects may have been ill when they entered the study. In other words, it may not have been a low sodium intake that caused their illness, but an illness that caused their low sodium intake. As the authors acknowledged, this problem (known as reverse causation) “cannot be ruled out and may account in part for the increased risk observed in the group of participants with a low estimated sodium excretion."
Second, only about 14 percent of the participants in the PURE study came from high-income countries like the United States. Roughly 60 percent came from China, India, and other lower-income countries where other factors might have altered sodium intakes and the risk of dying. There is no evidence that the people who consumed the least sodium were doing so to protect their health. As the O’Donnell paper notes, “our findings should not be interpreted as evidence that the intentional reduction of sodium intake would alter the risk of death or cardiovascular disease.”
Third, the PURE studies relied on a single urine sample to estimate each person's long-term sodium intake. In contrast, the best U.S. cohort study, a follow-up of the Trials of Hypertension Prevention, used multiple 24-hour sodium measurements, and it found that people with lower sodium intakes have a lower risk of cardiovascular disease.
A third study (by Mozaffarian et al.) in the same journal quantifies the massive toll caused by high-sodium diets and indicates why it is imperative for health officials around the world to institute policies to reduce sodium consumption. Americans are consuming about 4,000 mg of sodium per day—twice as high as those researchers recommend. As a result, tens of thousands of Americans die prematurely every year due to cardiovascular disease. In 2010 the Institute of Medicine urged the Food and Drug Administration to set limits on the sodium content of foods. Unfortunately, the FDA has not yet done anything.