Watch the salt, watch the salt, right? The findings of a new study in the Journal of the American Medical Association suggest otherwise. Researchers found that low-salt diets increased the risk of death from heart attacks and strokes and did not prevent high blood pressure.
These results run so counter to what has become standard nutritional advice that the Centers for Disease Control and Prevention have spoken critically of the study as flawed.
All the participants in the study were 3,681 middle-aged Europeans who did not have high blood pressure or cardiovascular disease. Researchers followed them for an average of 7.9 years. They assessed the subjects’ sodium content at the start and conclusion of the study by measuring the amount of sodium excreted in urine within 24 hours, the most precise way to measure sodium consumption as the body eliminates all sodium consumed within a day. Here’s what they found, as summarized in the New York Times:
The investigators found that the less salt people ate, the more likely they were to die of heart disease — 50 people in the lowest third of salt consumption (2.5 grams of sodium per day) died during the study as compared with 24 in the medium group (3.9 grams of sodium per day) and 10 in the highest salt consumption group (6.0 grams of sodium per day). And while those eating the most salt had, on average, a slight increase in systolic blood pressure — a 1.71-millimeter increase in pressure for each 2.5-gram increase in sodium per day — they were no more likely to develop hypertension.
“If the goal is to prevent hypertension” with lower sodium consumption, said the lead author, Dr. Jan A. Staessen, a professor of medicine at the University of Leuven, in Belgium, “this study shows it does not work.”
Dr. Peter Briss of the CDC raised the following concerns about the study:
…the study was small; that its subjects were relatively young, with an average age of 40 at the start; and that with few cardiovascular events, it was hard to draw conclusions. And the study, Dr. Briss and others say, flies in the face of a body of evidence indicating that higher sodium consumption can increase the risk of cardiovascular disease.
Dr. Briss points out that subjects who consumed the smallest amount of sodium also provided less urine, leading him to note that they may not have collected all of their urine on a 24-hour period. Other scientists, including Dr. Frank Sacks of the Harvard School of Public Health and Dr. Michael Alderman, the editor of the American Journal of Hypertension, hone in on the study’s flaws, while noting that the “medical literature on salt and health effects [is] inconsistent.” Dr. Alderman himself has done a study that found that, for those with high blood pressure, those most likely to die had a low-salt diet; he notes that the effects of a low-salt diet include insulin resistance, which can increase the risk of heart disease.
Scientists also are wary of the JAMA study’s results because it is an observational study rather than one involving randomized controlled clinical trial in which participants would be randomly assigned to follow a low-sodium diet or not over a period of years, and then have their health assessed and the deaths from cardiovascular disease noted. While some of the scientists argue that such a clinical trial is not feasible, Dr. Alderman (who, it should be noted, “once was an unpaid consultant for the Salt Institute but … [now does] no consulting for it or for the food industry”) says that doing such a clinical trial could be done, if public health researchers truly felt the need to do so.
Certainly it’s not easy to avoid eating a lot of salt if your diet includes a lot of processed and fast foods. The Recommended Daily Allowance (RDA) for sodium for an adult is to consume less than 2400 milligrams (mg) — about a teaspoon — of salt a day. Take a look at the ingredients for many items on the menus of McDonalds or for Mexican chains and your blood pressure might go up just seeing that more than a few items contain at least 1000 mg of sodium (and some far more). The body does need sodium so one doesn’t want to cut out all sodium from one’s diet, but it’s probably still a good idea not to go crazy with the salt shaker and to think twice before pouring out the soy sauce (914 mg in one tablespoon).
Photo by SoraZG