A long-running debate over the merits of eating less salt when one of the most comprehensive studies yet suggested cutting back on sodium too much actually poses health hazards.
Current guidelines from U.S. government agencies, the World Health Organization, the American Heart Association and other groups set daily dietary sodium targets between 1,500 and 2,300 milligrams or lower, well below the average U.S. daily consumption of about 3,400 milligrams.
The new study, which tracked more than 100,000 people from 17 countries over an average of more than three years, found that those who consumed fewer than 3,000 milligrams of sodium a day had a 27% higher risk of death or a serious event such as a heart attack or stroke in that period than those whose intake was estimated at 3,000 to 6,000 milligrams. Risk of death or other major events increased with intake above 6,000 milligrams.
The findings, published in the New England Journal of Medicine, are the latest to challenge the benefit of aggressively low sodium targets—especially for generally healthy people. Last year, a report from the Institute of Medicine, which advises Congress on health issues, didn't find evidence that cutting sodium intake below 2,300 milligrams reduced risk of cardiovascular disease.
The new report has shortcomings, and as an observational study it found only an association, not a causative effect, between very low sodium and cardiovascular risk. Still, it spurred calls to reconsider the targets. This "adds a pretty big weight on the side that low salt intake is associated with harm," said Suzanne Oparil, professor of medicine at the University of Alabama at Birmingham and an expert on high blood pressure. Without evidence from randomized trials to back them up, the low-sodium targets are "questionable health policy," she said. Dr. Oparil was author of an editorial that accompanied the findings.
"It's about time that major groups who are making recommendations on sodium take a more measured approach," said Salim Yusuf of the Population Health Research Institute, or PHRI, at McMaster University in Ontario and senior author of two papers on the new study.
The American Heart Association, a strong proponent of the low-sodium targets, isn't persuaded. Certain methods in the study, including how dietary sodium was estimated from urine samples, call "into question our ability to have confidence" in the findings, said Elliott Antman, AHA president.
"We hold fast to the recommendations that there is a need to reduce sodium intake in the diet," said Dr. Antman, a cardiologist at Brigham and Women's Hospital in Boston.
The Food and Drug Administration said it intends to review the studies. The agency said it "continues to recognize the need to reduce the sodium content of the food supply" to help reduce sodium intake.
Participants in the study, known as the Prospective Urban Rural Epidemiology study, or Pure, consumed an average of 4,930 milligrams of sodium a day, based on estimates derived from a single urine sample obtained when they enrolled in the study. The research was funded through a variety of public, private and corporate sources, according to PHRI.
Researchers followed participants for an average of 3.7 years. They found that 4.3% of those who consumed less than 3,000 milligrams of sodium either died or suffered a heart attack or stroke or developed heart failure in that time, versus 3.1% with intake between 3,000 and 6,000 milligrams. The percentage rose to 3.2% at levels above 6,000 milligrams and to 3.3% above 7,000 milligrams.