Too Little Dietary Salt Increases Cardiovascular Risks

Two new studies suggest that while high levels of sodium are harmful, eating too low an amount is harmful as well.

Researchers at McMaster University (Hamilton, ON, Canada), the Chinese Academy of Medical Sciences (Beijing) and other institutes participating in the Prospective Urban Rural Epidemiology (PURE) investigation obtained morning fasting urine samples from 101,945 persons in 17 countries, estimating 24-hour sodium and potassium excretion (used as a surrogate for intake). The researchers then examined the association between estimated urinary sodium and potassium excretion and the composite outcome of death and major cardiovascular (CV) events, such as heart attack or stroke.

The results showed that that those who consumed fewer than 3,000 mg of sodium a day had a 27% higher risk of death or a serious CV event than those whose intake was estimated at 3,000–6,000 mg. Risk of death or other major events increased with intake above 6,000 mg. The association between a high estimated sodium excretion and the composite outcome was strongest among those with hypertension. The researchers concluded that a sodium intake of 3–6 grams per day was associated with a lower risk of death and CV events. The studies were published in the August 14, 2014, issue of the New England Journal of Medicine (NEJM).

“Only one in 20 people in the world eat currently what is recommended. It indicates that we are making recommendations that most people can't meet; it's not a practical recommendation,” said study coauthor Andrew Mente, PhD, an assistant professor of clinical epidemiology and biostatistics at McMaster. “This suggests that rather than focusing on sodium, we should focus on eating an overall healthy diet and pursuing healthy lifestyle changes.”

“If they do not have hypertension they are not obese, and are younger, they really shouldn't worry too much about salt,” commented Suzanne Oparil, MD director of the vascular biology and hypertension program at the University of Alabama (Birmingham, USA), in an accompanying editorial. “They should do other good things, like have high levels of physical activity and eat a healthy diet. There's no demonstrable benefit of extreme sodium reduction, and we shouldn't be so focused on it.”

The findings run counter to current guidelines of the American Heart Association (Dallas, TX, USA) and other groups for heart disease prevention, which set daily dietary sodium targets between 1,500 and 2,300 milligrams or lower, well below the average daily consumption in the United States of about 3,400 mg. The recommended amount of sodium equals to 7.5–15 grams of table salt.

Related Links:
McMaster University
Chinese Academy of Medical Sciences
American Heart Association