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 |  Subject: Merry-Go-Round Continues: Low-Salt Diets May Pose Health Risks, Study Finds  Thu Aug 14, 2014 9:56 pm | |
| Findings Are Latest Challenge to Benefits of Aggressively Low Sodium Targets
A long-running debate over the merits of eating less salt escalated Wednesday 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 McMasters 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.
Sodium, the main component of salt, is a nutrient that is key to many cellular functions, many of which would likely "function on a lower level" with low sodium levels, said Niels Graudal, an internal-medicine specialist at Copenhagen University Hospital in Denmark who wasn't involved in this study. Too little sodium could trigger a hormonal response from the renin-angiotensin system that regulates blood pressure and actually increase blood pressure, researchers said. Very low sodium is also associated with higher blood fats called lipids, another risk for cardiovascular disease, Dr. Graudal said.
Little is known about what the right sodium levels are, but high levels are associated with high blood pressure, also known as hypertension—a key risk factor for heart attacks, strokes and heart failure. Estimates are that more than one billion adults world-wide have hypertension.
Current guidelines are largely derived from short-term studies that found that low-salt diets helped people already diagnosed with hypertension or with borderline high blood pressure to get their readings significantly lower.
But studies that show the resulting blood-pressure reduction in such patients reduces risk of death or serious cardiovascular problems are lacking.
"There is not a single study, not one, showing [such a] benefit for having a sodium intake of less than 2,300 milligrams," said Brian Strom, chancellor of Rutgers Biomedical and Health Sciences in New Jersey who wasn't involved in the study but chaired the Institute of Medicine panel that reported on sodium last year.
Dr. Antman of the AHA said conducting a long-term randomized trial to prove such a benefit would be "very challenging."
Absent that, the heart association believes other research, including a recent British study associating a reduction of salt intake in the population during the past decade with a lower rate of death from stroke and heart disease, support aggressive dietary sodium targets.
Underscoring the divide among heart experts over sodium intake levels, a separate study Wednesday in NEJM, from researchers at the Harvard School of Public Health, estimated that globally, there were 1.65 million deaths from cardiovascular causes in 2010 attributed to sodium consumption above 2,000 milligrams a day. The findings were derived from a complex calculation of results from 107 randomized studies and other data.
Dr. Antman said the result offered "a sense of the staggering numbers of people who are dying" from excess dietary sodium. Dr. Oparil, who is a past president of the heart association, termed researchers' efforts "herculean," but said because of the "lack of high-quality data" and "numerous assumptions" that went into the analysis, "caution should be taken in interpreting the findings."
Dr. Antman also said that the effect of a high-sodium diet accumulates over many years, leading to elevated blood pressure and a stiffening of blood vessels that results in increased risk for heart disease and strokes.
Reducing dietary sodium has been a public-health goal for several decades, but meeting the recommended targets is a daunting challenge for most people. Fewer than 1% of Americans are now in compliance, Dr. Strom said. More than three-quarters of dietary sodium comes not from the salt shaker but from processed food and restaurant fare, according to the FDA. Grocery-store aisles and restaurants, according to information on a Texas A&M University website, are rich in sodium: 264 milligrams in two slices of whole-wheat bread; 1,107 in a cup of chicken noodle soup; 639 in a hot dog; 1,093 in a frozen pot pie; 709 in a fast-food cheeseburger.
Such levels help explain calls for efforts to work with food makers to reduce sodium content. "Very high levels of sodium intake appear to be associated with bad outcomes," said Michael Lauer, director of cardiovascular sciences at the National Heart, Lung and Blood Institute. "That's an important message to keep in mind."
http://online.wsj.com/articles/recommended-salt-levels-could-do-more-harm-than-good-study-suggests-1407964274 |
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