July 6, 2011 -- Contrary to what medical experts have been saying for years, a new study suggests 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 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.
But this finding doesn't mean people can eat 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.
"We would require some 2,500 cardiovascular events in over 18,000 trial participants to detect a small reduction in relative risk," they wrote. They also said that the study subjects only moderately lowered their sodium intake, so the effect on blood pressure and heart disease was small.
Numerous experts who were not involved with this research weighed in on the findings, and their opinions are mixed. 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 a role sodium plays in the development of heart disease.
"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," said Dr. Salim Yusuf, professor of medicine at McMaster University in Hamilton, Ontario, Canada. 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.
"I have always viewed the data for salt shortening life as being very weak," said Dr. Ken Fujioka, director of the Nutrition and Metabolic Research Center at Scripps Health in San Diego.
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.
"[R]educing 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.
"We do know that high blood pressure, while associated with all forms of cardiovascular disease, is particularly associated with risk for stroke," said Dr. Merle Myerson, director of the Cardiovascular Disease Prevention Program at St. Luke's-Roosevelt Hospital in New York.
Dr. Clyde Yancy, chief of the Division of Cardiology at Northwestern University's Feinberg School of Medicine, said 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."
Salt Part of a Heart-Unhealthy Diet
"If someone gets large amounts of salt in their diet, it may be an indicator of a bad diet," said Keith Ayoob, associate professor of pediatrics at the Albert Einstein College of Medicine in the Bronx, N.Y.
"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."
Experts recommend taking these findings with a grain of salt and focusing efforts on other ways to prevent cardiovascular disease, such as eating more fruits and vegetables and exercising. They do, however, suggest avoiding excessive salt consumption.
"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.
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.
"1,500 mg/day is actually lower than the typical hospital's 'low-sodium diet' of 2,000 mg/day," Ayoob said.
"I do generally recommend lowering salt intake, but don't push it too hard, and focus more on calories and exercise," said Dr. Christopher Cannon, a physician at Brigham and Women's Hospital in Boston.
"People get treated for their blood pressure with medicine now," said Dr. Louis Aronne, clinical professor of medicine at NY-Presbyterian/Weill Cornell Medical Center. "There are so many medicines that are effective, with so few side effects, it makes me wonder if dietary restriction is useful."
Some people, such as the approximately 1 in 4 who are not sensitive to the effects of salt as well as those who are healthy and don't have high blood pressure should focus on other methods of preventing heart disease.
"If they do not have high blood pressure that is responsive to salt and the salt helps them eat healthy foods then they should not stop," Fujioka said.
"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."
Additional reporting by ABC News' Jane Kurtzman and Bojana Zupan.