Salt intake study causes confusion

By Dr. Ananya Mandal, MDJul 7 2011

A new review of studies refutes earlier knowledge and says salt may not be as bad for the heart as commonly believed. Researchers from the Universities of Exeter and Plymouth in Exeter, U.K. reviewed data for the Cochrane Library from seven studies with nearly 6,500 participants who reduced their salt intake and found that while eating less salt did lower blood pressure, it did not reduce the risk of dying or of having heart disease.

However the team warns this does not allow people to have as much salt as they want. The authors caution that they don't have enough data to come to any firm conclusions about salt intake and heart disease. They wrote, “We would require some 2,500 cardiovascular events in over 18,000 trial participants to detect a small reduction in relative risk.” They also said that the study subjects only moderately lowered their sodium intake, so the effect on blood pressure and heart disease was small.

Other experts who were not part of the study gave mixed opinions. They agree more data are needed to provide a better explanation of the findings and that there are other limitations to the study design, but debate how big role sodium plays in the development of heart disease.

Dr. Salim Yusuf, professor of medicine at McMaster University in Hamilton, Ontario, Canada said, “

I had been long concerned that the bold and strident public health recommendations of trying to reduce salt intake in Western societies was not based on robust data and may be premature.” The studies reviewed by the authors, he said, suggest the relationship between salt consumption and cardiovascular disease is complex and requires more research. This research should be a priority, he added.

Dr. Ken Fujioka, director of the Nutrition and Metabolic Research Center at Scripps Health in San Diego also said, “I have always viewed the data for salt shortening life as being very weak.” But other experts say salt does contribute to heart disease and other life-threatening conditions, which can lead to an untimely death in the long term. “There is extensive evidence that excessive salt intake places many individuals at risk for hypertension and cardiovascular disease. These long term effects may not result in death for many years,” said Dr. Pascal Imperato, dean of SUNY Downstate Medical Center's School of Public Health in Brooklyn, N.Y. “Reducing blood pressure does reduce the risk of cardiovascular disease and related mortality,” said Dr. Redford Williams, director of the Behavioral Medicine Research Center at Duke University in Durham, N.C.

Dr. Merle Myerson, director of the Cardiovascular Disease Prevention Program at St. Luke's-Roosevelt Hospital in New York added, “We do know that high blood pressure, while associated with all forms of cardiovascular disease, is particularly associated with risk for stroke.” Dr. Clyde Yancy, chief of the Division of Cardiology at Northwestern University's Feinberg School of Medicine was skeptical since prior research does support the conclusion that restricting sodium can lead to “fewer deaths and much less money spent on health care for blood pressure-related diseases.”

”The data are not strong enough to recommend marked sodium restriction for the entire country, but I also do not believe that these data negate the overall recommendations to at least avoid excessive salt,” said Dr. Carl Lavie, medical director of Cardiac Rehabilitation and Prevention at the John Ochsner Heart and Vascular Institute in New Orleans.

“Foods that are staples in the U.S. tend to be high in both sodium and fat. Reducing the intake of many of these foods would reduce body weight, which would have a significant effect on blood pressure and [cardiovascular disease],” said Carla Wolper, an obesity researcher at St. Luke's-Roosevelt Hospital. “If Americans really reduced salt consumption, they would most likely also be lowering fat intake and thus caloric intake.”

The U.S. Dietary Guidelines recommend no more than 1,500 milligrams of sodium a day for all African Americans and other adults older than 50, but some believe this is overly restrictive. In Britain, the National Institute of Health and Clinical Guidance (NICE) has called for an acceleration of the reduction in salt in the general population from a maximum intake of 6 grams(g) a day for adults by 2015 to 3g by 2025.

“There is a healthy amount of sodium we all need in our diet,” said Dr. Stephanie Moore, a cardiologist at Massachusetts General Hospital in Boston. “Define [a] healthy amount of sodium - there is the study we need.”