Exercise may not be good enough
to reduce mild hypertension in older people
Newswise — 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.
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