Excess salt is harmful, concluded a recent study, while a second study—which had serious shortcomings—suggested that too little salt can also be dangerous.
An estimated 1.65 million deaths from cardiovascular disease worldwide in 2010 were caused by sodium intakes over 2,000 milligrams a day, according to the first study. It used the results of 103 trials to estimate the effect of sodium on blood pressure, and data on 1.38 million people to estimate the effect of blood pressure on strokes and heart attacks.
The second study reported an increased risk of strokes, heart attacks, and deaths in people who had not just higher sodium intakes (over 6,000 mg a day) but also in those who had lower intakes (below 3,000 mg a day). However, as the authors acknowledged, “reverse causation” couldn’t be ruled out as a cause of the higher risk in people who ate less salt. In other words, it’s possible that eating less salt didn’t cause their illness, but that illness caused them to eat less salt. (People who are sick often eat less food.) As the authors stated, there is no evidence that any of the 102,000 participants—60 percent of whom were from China, India, and other lower-income countries—were intentionally eating less salt to protect their health.
The American Heart Association, which stands by its advice to limit sodium to 1,500 mg a day, has documented potential flaws in studies like the second one. Unfortunately, an editorial published with the studies—written by a former consultant to the Salt Institute (and expert witness for the tobacco industry)—did not cite those flaws.
What to do: Cut back on salt in prepared foods and the salt shaker.
Sources: N. Engl. J. Med. 371: 612, 624, 677, 2014; Circulation 129: 1173, 2014.