Study Shows Reducing Salt Lowers Blood Pressure; Evidence Inconclusive on Preventing Heart Disease
By Kathleen Doheny
WebMD Health News
Reviewed by Louise Chang, MD
July 6, 2011 -- Reducing salt intake in the diet produces a small decline in blood pressure, according to a new review of research. But the evidence is not conclusive on whether salt reduction has an effect on getting cardiovascular disease or dying from it, the researchers say.
The findings are not a call to eat salt with abandon, warns researcher Rod Taylor, PhD, MSc, professor of health services research at the University of Exeter in the U.K.
The review evaluated nearly 6,500 people and is published online in the American Journal of Hypertension and the Cochrane Database ofSystematic Reviews 2011.
Taylor suspects he found no strong evidence that salt reduction lowered heart disease risk and death because the numbers studied were too small. And those studied may have lowered salt intake at first but then slid back into old habits, he says.
In the short term, up to two years after study participants were advised to reduce salt, he found a trend of reduced deaths, Taylor tells WebMD. "In the longer term, out about 10 years, that benefit disappeared. And we believe that is because people were not able to maintain that behavior."
"What this says is, giving people advice to reduce their dietary salt is not enough on its own," Taylor says.
What is needed is a multi-pronged approach, he says, including better labeling, at least in the U.K., and government help, along with more research studies looking at the link.
However, the Salt Institute sees the new findings differently. In a statement, the industry group said the new findings are reason for the government to end efforts to reduce salt intake until a benefit can be proven.
Salt and Heart Disease
Taylor's team looked at seven published studies that included nearly 6,500 participants. Some participants had normal blood pressure and some had high blood pressure. One study looked at salt restriction in people with heart failure.
Reducing salt was linked with a mild reduction in blood pressure. Systolic blood pressure decreased slightly, by about 1 to 4 points. Systolic pressure is a measure of pressure while the heart is beating. It is the top number of the reading.
However, the researchers found that salt restriction increased the risk of death from all causes in those with heart failure.
They concluded there was not enough evidence to say whether the reduced salt had an effect on cardiovascular deaths in the other participants.
A large-scale clinical trial looking at the impact of dietary salt reduction on health outcomes is needed, according to the Salt Institute.
In the statement, Mort Satin of the Salt Institute says health policy on salt set by the government needs to be based on evidence. "The public health agencies have deliberately ignored the preponderance of clinical evidence in order to pursue a reckless salt reduction agenda based far more on ideology than science," according to Satin.
Perspective of American Heart Association
In a statement issued today, the American Heart Association (AHA) points out some shortcomings of the study. The studies included mostly middle-aged white or Asian people, for instance, yet high blood pressure is more common among older Americans and African-Americans. Also, the organization says the follow-up may not have been long enough, as heart disease and stroke risk develop slowly.
The American Heart Association stands by its sodium advisory issued earlier this year, according to a spokesperson.
The AHA calls for consumers, the U.S. government and the food industry to step up efforts to reduce salt intake.
The AHA recommends the general population eat no more than 1,500 milligrams of sodium a day. It cites ill effects of excess salt on blood pressure and a higher risk of kidney disease, stroke, and heart attack.
Currently, Americans eat more than two times the recommended maximum of 1,500 milligrams daily, according to the AHA.
A fast-food double cheeseburger, for instance, has about 1,051 milligrams of sodium, according to the U.S. Department of Agriculture (USDA).
The study results won't change the advice given by Suzanne Steinbaum, DO, preventive cardiologist at Lenox Hill Hospital in New York. "Based on this study, I will continue to advise people to reduce the amount of salt in their diet," she tells WebMD.
She points to the reduction in blood pressure found. Based on that, she says, she would expect a health benefit. "More studies need to be done," she agrees. "But at this point, I think we really need to continue to advise salt reduction."
Gordon Tomaselli, MD, president of the American Heart Association and chief of cardiology at Johns Hopkins University School of Medicine, says he will not change his advice for patients. "I would still tell people they should continue to keep the salt in their diet low."
While the AHA recommends 1,500 milligrams a day maximum for everyone, he says the USDA recommendation is to limit sodium to less than 2,300 milligrams for the general population but less than 1,500 milligrams for people age 51 or older and people of any age who are African-American or have high blood pressure, diabetes, or chronic kidney disease.