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,
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," said exercise
physiologist Kerry J. Stewart, professor of
medicine and director of clinical and research exercise
physiology programs at the Johns Hopkins 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, said Stewart, who led the new study,
examined mostly younger men in whom high blood pressure has
different characteristics and causes than in older people.
Hypertension in younger adults is often due to a high
cardiac output when at rest and during exercise, when 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 Johns 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 Johns 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, Johns
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
nonexercising 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
nonexercisers.
Diastolic reductions were significant, at 3.7 mm/Hg
for exercisers and 1.5 mm/Hg for nonexercisers,
respectively, indicating a distinct advantage for
exercisers.
According to Stewart, it remains unclear why the
systolic blood pressure dropped nearly as much in
nonexercisers as the exercising group. Among nonexercisers,
it may be due to the placebo effect, which is common in
blood pressure studies, the researcher said. The smaller
than expected drop in systolic blood pressure could also be
due to 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 added.
Upon closer examination, the Johns 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," Stewart said. "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," he said, "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," Stewart added. "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 had 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, and the Johns Hopkins Clinical Research Center,
also part of the NIH.
Other investigators in this research were Anita
Bacher, Katherine Turner, Jerome Fleg, Paul Hess, Edward
Shapiro, Matthew Tayback and Pamela Ouyang.