Moderate exercise is not enough to control mildly elevated blood pressure in men and women over 55, Johns Hopkins University researchers report.

The finding casts doubt on the effectiveness of some recommendations on exercise for lowering blood pressure among those in the age group most at risk of a heart attack, the researchers added. Guidelines from the American College of Sports Medicine, for example, recommend 30 to 45 minutes of aerobic exercise and moderate weightlifting three to five times a week.

However, the new study suggests these guidelines may be wrong, at least as far as older people are concerned. "We found that exercise in people between the ages of 55 to 75 may not be as effective in lowering blood pressure as previously believed, based on published guidelines," said lead researcher Kerry J. Stewart, a professor of medicine and director of clinical and research exercise physiology at Johns Hopkins School of Medicine.

The study results appear in the April 11 issue of the Archives of Internal Medicine.

According to the American Heart Association, blood pressure is the force in the arteries when the heart beats -- called systolic pressure -- and when the heart rests -- called diastolic pressure. Systolic pressure is the "upper" number in a blood pressure test, while diastolic pressure is the lower. The readings are measured in millimeters of mercury (mm Hg).

For the study, Stewart's team randomly assigned 104 men and women to six months of a program that combined increased aerobic exercise and weightlifting, or to six months of their usual diet and activity -- or inactivity. All participants had systolic blood pressure of 130 to 159 mmHg and diastolic pressures of 85 to 99 mmHg. The recommended blood pressure is 120/80 mmHg.

There were 51 people in the exercise group and 53 in the non-exercise group. "After six months of exercise, exercise did lower systolic blood pressure by about 5 mmHg, but there was a similar drop in the non-exercising group," Stewart said. "This makes it difficult to attribute the change in blood pressure solely to exercise."

Likewise, both groups had a reduction in diastolic pressure, "but, with a greater reduction in the exercisers," Stewart said.

Stewart attributed the similar drop in blood pressure in both groups to the so-called placebo effect. "People in a study get benefits just by the fact they are in a study," he explained.

Looking at the stiffness of the blood vessels, which is a major cause of high blood pressure in older people, the researchers found that exercise did not alter the existing stiffness, which could explain the less-than-expected drop in blood pressure, he said.

"Despite the fact that older people got very fit and lost fat and gained muscle, the systolic blood pressure was not lowered to the level expected," Stewart said. "This study raises questions as to whether the kinds of exercises that have been suggested for everyone to lower their blood pressure may not be as effective in older people."

Stewart said the study results suggest that exercise may not be enough for older people with high blood pressure. "Perhaps they need to start [blood pressure] medicine sooner or lose weight more quickly. Those who had the greatest drop in blood pressure were the ones who lost the most weight."

This finding doesn't mean that older people shouldn't exercise, Stewart said. "People should continue to exercise. We saw tremendous changes in fitness. We saw very important shifts in body composition, much less fat, much more muscle. But to control blood pressure, they may need to talk with their doctor and start medications sooner or perhaps get their weight down through diet, and not rely solely on exercise."

Dr. Franz H. Messerli, director of the hypertension program at St. Luke's-Roosevelt Hospital in New York City, has another explanation for why exercise didn't significantly lower blood pressure in the study participants. As a rule, the blood pressure of older patients is more likely to respond to blood pressure drugs than younger patients, he said.

"While this is true for most antihypertensive drugs, it is not the case for beta-blockers," he said. "If anything, the elderly respond less well to beta blockade than does the younger patient. The lesser response to beta blockade may be related to the heart rate-lowering effect of these drugs, Messerli explained.

And exercise's effect on the cardiovascular system has been said to be like a "physiologic beta blockade," he noted. "Conceivably, the greater decrease in heart rate seen in the exercise group could at least to some extent explain the lack of an effect on systolic and the enhanced effect on diastolic pressure in the present study."

However, Messerli said, one also has to take into account that blood pressure was falling in the non-exercise group as well. "Most likely, they tried to please their physicians by following a healthier lifestyle, which also leads to a decrease in blood pressure."

More information on High Blood Pressure