January 5, 2001

In two studies released this week, the impact of diet and weight control on high blood pressure was strongly reaffirmed. More than 80 percent of people over 50 are said to have some degree of high blood pressure.

In a study conducted by Harvard University scientists and published in the current issue of The New England Journal of Medicine, investigators found that a low-salt diet combined with a diet rich in fruits, vegetables and other healthy foods can significantly lower blood pressure.

In other research, at the Kaiser Permanente Center for Health Research in Oregon and published in The Annals of Internal Medicine, even modest weight loss was shown to have a long-term lowering effect on high blood pressure and could even replace the anti-hypertension medicines many of the subjects were taking.

The Harvard study, too, noted that cutting sodium intake could be as effective at lowering blood pressure as medication, particularly when accompanied by a closely controlled diet.

Current salt guidelines call for less than 2.3 grams of sodium (or about one teaspoon of sodium chloride) daily, but the average American eats about 50 percent more than that, generally in prepared foods.

In the late 1990s, scientists reported that eating lots of fruit, vegetables, grains, low-fat dairy foods, and a diet that favored poultry and fish over red meat, could significantly reduce blood pressure.

That study's recommended diet, called the Dietary Approaches to Stop Hypertension (DASH) diet included advice, including eating foods low in cholesterol and saturated fats and rich in calcium, potassium and other important nutrients, the became part of national guidelines for blood pressure control.

The latest study focused on whether limiting sodium intake would lower blood pressure beyond the effects of a DASH regimen. The researchers compared effects on blood pressure of three sodium levels: high, or what the average American gets; a medium, recommended level of 2.3 grams a day, and low, which tried to keep daily intake under 1.5 grams.

For 30-day stretches, 412 men and women consumed either a typical American diet or the DASH diet. For all three salt levels, subjects on the DASH diet lowered their blood pressure more than those in the control diet group, suggesting that a healthy balanced diet was important to follow along with the salt restrictions.

Compared with those on a high salt control diet, subjects with high blood pressure who ate the lowest-salt DASH regimen reduced their systolic pressure (the top number in the two-part reading) by an average 11.5 millimeters of mercury. That's as much as a drug could be expected to lower blood pressure. For subjects without hypertension, the average decrease was about 7 millimeters.

Regardless of which diet they followed, or whether they had hypertension, subjects who cut their salt intake reduced their blood pressure. The impact was smaller, though still significant, when subjects reduced salt from high to medium, or medium to low. The findings also held for blacks, who suffer disproportionately from high blood pressure.

"These drops in blood pressure are what you get in drug therapy. We're not quibbling about a little effect," said Dr. Frank Sacks, an associate professor of nutrition and medicine at Harvard and lead author of the study. For instance, he says a nine-point decrease in systolic pressure can mean a 30 percent reduction in cardiovascular risk. Sacks said the study suggests the current guidelines for salt intake may be too high, and that lowering the recommended daily amount by 50 percent might be warranted.

But dietitians who helped develop the DASH diet say that it would be unreasonable to expect people to cut their salt intake by half on their own and that the food industry might have to help by producing more low-salt processed foods, much the way that food makers have developed a wide range of low-fat edibles.

Although Sacks noted to an online health reporter that low-salt foods might be short on taste, generous spicing, like the recipes used in the DASH diet, more than make up for the missing sodium. "The real key is to get a mixture of herbs and spices," he says.

The Oregon study similarly showed that dietary changes, along with physical activity and social support to help make the weight loss permanent, could reduce high blood as effectively as medications.

The Kaiser Permanente researchers analyzed data on 1,191 adults, age 30 to 54, who were 10 percent to 65 percent above their ideal body weight. All were considered to have the first stage of hypertension, with readings on the high side of normal.

Half the people were assigned to a weight-loss program that included counseling and focused on diet, physical activity and social support. The others were left to their own devices, receiving regular medical care, but no special treatment to encourage weight loss.

Weight and blood pressure readings were taken every six months for three years. At the benchmarks of six, 18 and 36 months, the group that was counseled, on average, lost weight, while the other group continued to put on pounds. However, the number of people who maintained their weight loss was modest.

Patients who lost at least 10 pounds over three years had the biggest reduction in blood pressure. If they maintained their weight loss for the three years, they had a 65 percent lower chance of hypertension, wrote Dr. Thomas G. Pickering, of Mount Sinai Medical Center in New York City, in an accompanying editorial.

"That's really good news," he said. "Some blood pressure drugs also reduce blood pressure and risk of heart disease, but they can cause other problems. Most people, if they could do it (reduce blood pressure) without drugs, they would."

Clearly, though, keeping weight off is a difficult matter for many dieters, and the importance of exercise and counseling cannot be overestimated.

At Sharp, The Center for Health Promotion sponsors group weight loss programs and individual counseling.

For more information, go to:
http://www.sharp.com/clinical/chp/

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