Holding That Grain of Salt

In 1997, the Dietary Approaches to Stop Hypertension (DASH) trial showed that a diet high in fruits, vegetables and lowfat dairy products could help reduce blood pressure, especially in people with hypertension.

Four years later, the DASH team, led by Associate Professor of Nutrition Frank Sacks of the School of Public Health, is back fighting high blood pressure.

In a study published last week in the New England Journal of Medicine, Sacks and his team show that combining the DASH diet with a reduction in salt intake can further reduce high blood pressure, especially in those with hypertension.

"This is pretty much a definitive result that now needs application," Sacks says.

The team, which consisted of researchers at Harvard, Duke, Johns Hopkins and Louisiana State, tested 412 people, assigning half of them to the DASH diet and half of them to a normal diet. The subjects then ate foods with high, medium and low sodium for 30 consecutive days.

The results showed that combining the DASH diet with a low sodium intake reduced blood pressure by an average of 7.1 points in healthy patients, and by 11.5 points in patients with hypertension.

Reduced salt intake led to a decrease in blood pressure both in patients who were on the DASH diet and those who were on the control diet.

Likewise, patients using the DASH diet, which Sacks said includes "a lot of vegetables, whole grains, fruits, fish and poultry instead of red meat, and fewer sugary desserts and drinks," showed lower blood pressure than those on the normal diet at every level of salt intake.

About 50 million Americans suffer from high blood pressure, which kills more than 42,000 people and contributes to the deaths of 210,000 each year.

Sacks and the DASH team say the results make it clear that the government and food industry should work to reduce the level of salt intake in people's diets.

"The recommended upper limit [of sodium intake by the Food and Drug Administration] should be lowered," Sacks says. "[Food manufacturers] should reduce the amount of salt in the foods they make and prepare more low-salt varieties of foods, like they do with low-fat foods."

In the team's 1997 study, patients who had hypertension showed an 11.4-point decline in blood pressure when using the DASH diet.

In the recent study, a combination of the DASH diet and reduced salt intake resulted in an 11.5-point decrease.

This has led the Salt Institute, a non-profit association of salt producers, to claim that the DASH diet produced most of the effect and that efforts to combat hypertension should focus on that, rather than on reduction of salt intake.

"The new DASH-Sodium Study confirms that most of the blood pressure benefits of combining the DASH Diet with sodium reduction comes from the DASH Diet itself, not the amount of sodium in the diet." said Salt Institute President Richard L. Hanneman in a press release.

But according to Sacks, the DASH diet had a smaller effect on the population observed in the new study than it did in 1997; therefore, low salt intake made a significant contribution to the decrease in blood pressure in the recent study beyond what the DASH diet alone would have done.

"In the second study the DASH diet had a smaller effect," Sacks says. "I don't have an explanation other than that it was a different sample."

"The Salt Institute doesn't like to see anything that reduces salt intake," he adds.

Sacks says these results need no more testing, but that his future research may focus on the effects of other aspects of the diet on blood pressure.

"The most important thing [for the DASH diet and salt study] is implementation," Sacks says. "The food industry and the national and international health policy groups should take a look at this and should consider more stringent guidelines."