Moderate levels of exercise may not be enough to control mild hypertension

Apr 11 2005

Moderate levels of exercise may not be enough to control mild hypertension in men and women over age 55, the age group most at risk of later developing potentially fatal heart failure, a new four-year study reports. The findings by researchers at Johns Hopkins, to be published in the journal Archives of Internal Medicine online April 11, call into question the effectiveness of national guidelines on exercise for lowering blood pressure in older people.

Current guidelines from the American College of Sports Medicine recommend 30- to 45-minute periods of combined aerobic exercise and moderate weightlifting, three to five times per week, with an expected reduction in blood pressure of 8 millimeters to 10 millimeters of mercury (mm/Hg).

"Exercise is highly recommended for reducing blood pressure and is part of prevention and treatment programs for an estimated 90 percent of adults in the United States who eventually develop hypertension," says exercise physiologist Kerry J. Stewart, Ed.D., professor of medicine and director of clinical and research exercise physiology programs at The Johns Hopkins University School of Medicine and its Heart Institute. "But current exercise guidelines were based on studies that had several limitations, including that they were not tested in older adults."

Previous studies, says Stewart, who led the new study, examined mostly younger men in whom high blood pressure has different characteristics and causes than are the case in older people. Hypertension in younger adults is often due to a high cardiac output when at rest and during exercise, where the heart beats faster than it has to, he adds. However, hypertension in mature adults results from changes in the walls of the large arteries that carry blood throughout the body. These blood vessels become less elastic or flexible, a condition known as arterial stiffening, and this causes blood pressure to rise.

The Hopkins study, formally known as the Senior Hypertension and Physical Exercise study (or SHAPE, for short), is believed to be the first detailed examination of the guidelines' effectiveness and gender differences in the effects of exercise, with nearly an equal number of men and women enrolled. Moreover, its participants were not taking any drugs to reduce high blood pressure.

For a six-month period, the Hopkins researchers analyzed blood pressure in 104 men and women ages 55 to 75. Half were randomly placed in a standardized moderate exercise program while the rest maintained their usual physical routine and diet.

For those in the standardized program group, Hopkins arranged for supervised aerobic exercises, such as running on a treadmill and cycling, and strength exercises, like weightlifting. The exercise routine was performed three times per week, each session lasting 90 minutes, for a total of 78 sessions per exerciser during the study period. Measures of aerobic fitness and body fat were made at the beginning and end of the study.

Using ultrasound imaging, the researchers also examined "artery stiffness" in a subset of 82 study participants by gauging the velocity of pulse waves generated by heart contractions. Stiffer, less flexible arteries accelerate blood flow, creating faster pulse waves. Blood pressure is a measure of the force applied against the inner walls of arteries as the heart pumps blood around the body. The systolic reading (the "upper" number in a blood pressure test), measures the maximum pressure as the heart contracts, while the diastolic reading (the "lower" number) measures the force when the heart is at rest, between beats.

At the beginning of the study, mild hypertension was counted as between 130 and 159 mm/Hg for systolic pressure, or 85 to 99 mm/Hg diastolic. Most participants had systolic hypertension, when the systolic blood pressure is high and the diastolic blood pressure is normal. This is common in older people, and the average blood pressure at the start was 141 mm/Hg over 76 mm/Hg.

At the end of the SHAPE study, exercisers showed significant improvements in overall fitness, as measured by their performance on a treadmill and by how much weight they could lift. Improvements were also seen in body composition, such as increased lean muscle mass and reduced fat, especially fat surrounding the waist and inside the abdominal cavity. However, reductions in blood pressure were mixed, with both program exercisers and the non-exercising group lowering systolic blood pressure measurements by 5.3 mm/Hg and 4.5 mm/Hg. This reduction, while important, was not statistically different between the two groups. Similarly, measures of artery stiffness did not improve significantly in either exercisers or non-exercisers.

Diastolic reductions were significant, at 3.7 mm/Hg for exercisers and 1.5 mm/Hg for non-exercisers, respectively, indicating a distinct advantage for exercisers.

According to Stewart, it remains unclear why the systolic blood pressure dropped nearly as much in non-exercisers as the exercising group. Among non-exercisers, it may be due to the placebo effect, which is common in blood pressure studies, says the researcher. The smaller than expected drop in systolic blood pressure could also be due arterial stiffening, which did not improve in either group. Arterial stiffening causes higher systolic blood pressure rather than higher diastolic blood pressure, and older people may be resistant to reducing their systolic blood pressure even though they made substantial gains in fitness with exercise training, he adds.

Upon closer examination, the Hopkins team found that people most likely to decrease both systolic and diastolic blood pressure also were those who lost the most body fat, particularly abdominal fat, and gained the most muscle. These changes in body composition were more closely related to reductions in blood pressure than improvements in fitness. Overall, results for both improvements in fitness and body composition were nearly identical for men and women.

"Older people should still be encouraged to exercise because it produces numerous health benefits, but their expectations need to be modified about how much good the exercise alone will do for reducing systolic blood pressure. They may also need to understand it could take much more time for them to reach blood pressure goals, and it may require more intensive exercise programs. Although participants followed the prescribed program according to guidelines without fail, it does not seem to be enough for full blood pressure control in older people.

"Alternatively, older persons may need to get started sooner on medications to immediately bring blood pressure under control, rather than relying strictly on exercise, although a comparison of exercise to drugs requires further study.

"Our next research will continue to examine demonstrable benefits from exercise, in people at risk for heart disease," adds Stewart. "Further examination of the role of decreasing abdominal fat, which dropped nearly 20 percent in this study, and its link to lowering blood pressure, could also explain why exercise helps to improve overall heart health. We are also interested in learning if longer periods of exercise, or more intense exercise, may help reverse artery stiffness, which is an underlying cause of hypertension as people age."

High blood pressure forces the heart to pump harder to circulate blood throughout the body. As a result, the heart muscle abnormally grows larger and this can lead to heart failure. According to recent statistics from the American Heart Association, in 2002, 65 million Americans have high blood pressure. Normal blood pressure was most recently defined in 2003 by a national advisory committee to the United States Department of Health and Human Services as systolic pressure of 120 mm/Hg or greater, and/or a diastolic pressure of 80 mm/Hg or greater.

Funding for this study, which took place from July 1999 to November 2003, was provided by the National Heart, Lung and Blood Institute, part of the National Institutes of Health (NIH), and the Johns Hopkins Clinical Research Center, also part of the NIH.

Other investigators in this research were Anita Bacher, M.S.N., M.P.H.; Katherine Turner, M.S.; Jerome Fleg, M.D.; Paul Hess, Ph.D.; Edward Shapiro, M.D.; Matthew Tayback, Sc.D.; and Pamela Ouyang, M.D.