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 Exercise
Can Build Bones for Late Boomers, Senior Citizens
May 25, 2005 – New research says late Boomers and
Senior Citizens – those 55 to 75 - can sustain and maybe improve bone
mass with a moderate exercise program. The researchers say their results
debunk the myth that exercising to lose excess body fat, unlike
dieting alone, comes at a cost to bone health.
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The John Hopkins team showed, in a study to be
published in the June issue of the American Journal of Preventive
Medicine, that after six months of aerobic exercise on a treadmill,
bicycle or stepper, plus weightlifting, subjects experienced better
overall fitness and fat loss without much change in bone mineral
density.
A more detailed analysis revealed slight gains in
bone mass, of 1 percent to 2 percent, for those who exercised hardest
and showed the greatest increases in aerobic fitness, muscle strength
and muscle tissue.
The Hopkins study is believed to be the first to
evaluate the effects of exercise independently from other factors,
primarily diet, on bone mineral density, a strong gauge of bone health,
against the risk of osteoporosis and bone fracture. Indeed, the
researchers believe that more intense exercise may demonstrate
significantly increased bone mass.
"Older people are very concerned about how best to
reduce their body fat as a means of preventing other health problems,
such as heart disease and diabetes," says lead study investigator and
exercise physiologist Kerry Stewart, Ed.D., a professor of medicine and
director of clinical exercise physiology and heart health programs at
The Johns Hopkins University School of Medicine and its Heart Institute.
"However, excess fat does have the benefit of
maintaining bone mass. But fat loss through diet alone can lead to loss
of bone, worsening the body's natural bone loss due to aging, a major
risk factor for bone fractures," Stewart added.
According to Stewart, most existing studies about
the effects of exercise on bone had several limitations to their
findings. Many enrolled only women, for example, who are more prone to
bone loss after menopause. Others combined dieting and exercise,
obscuring the source of the impact. None examined the effects of
exercise on bone while also factoring into account the weight and fat
changes resulting from it.
For a six-month period, the Hopkins team assessed the benefits of a
supervised program of exercise training in a group of 104 older men and
women, measuring both fitness and fatness levels at the start and end of
the study.
All of the participants were in general good health
except for untreated, mild hypertension. Half were randomly placed in a
widely recommended moderate exercise program, believed to improve
fitness, heart health and body composition, while the rest maintained
their usual physical routine and diet.
The active group participated in a supervised
series of exercises for 60 minutes, three times per week. The
combination of exercises was designed to work all major muscle groups,
the heart and circulation.
Substantial improvements were observed in active
participants' body fat, and muscle and fitness levels.
Aerobic fitness, as measured by peak oxygen uptake
on a treadmill, increased by 16 percent, and strength fitness increased
by 17 percent. The average weight loss in this group was only four
pounds, because much of the loss of fat was offset by increased muscle
mass. The fat in the abdominal region, measured by magnetic resonance
imaging, was reduced by 20 percent among exercisers. The group that was
not exercising had either no or significantly less improvement than the
exercising group.
Bone scans, using an X-ray machine called DXA, were
used to assess bone mineral density. Measurements were taken of the
total skeleton and in areas most vulnerable to bone loss and subsequent
fracture, including three locations on the hip, and one in the spine. In
both men and women who exercised and lost weight, overall bone density
did not change, although results were mixed for women in specific sites
of the hip. However, those who showed the greatest gains in fitness had
modest gains in bone density at several sites, and loss of body fat was
not associated with bone loss.
According to Stewart, an increase in bone mineral
density among older exercisers has been observed in previous studies,
but this increase was lacking in the current study because the fitness
program was probably of too low intensity or too short in duration.
"Older people will likely have to exercise either
harder or for longer than six months for there for there to be a
substantial increase in bone density," says study co-author and
endocrinologist Suzanne Jan de Beur, an assistant professor at Hopkins
who specializes in bone health. "Our results show that
moderate-intensity exercise can increase fitness and reduce body fat,
which are important for overall health, but gains in bone density were
found only among those who achieved the greatest gains in fitness in six
months. Fat loss with exercise did not result in a loss of bone mass, a
problem commonly seen when patients lose weight with diet alone."
Jan de Beur adds that while bone mass did not
increase in this program, there are other benefits that will likely
reduce the risk of fractures. Bones commonly break after a fall, a major
risk factor for fractures in older people. But exercise makes bodies
stronger and improves balance, thus preventing falls.
The Hopkins study's exercise program followed
current guidelines from the American College of Sports Medicine. The
study was part of a larger, ongoing trial, called the Senior
Hypertension and Physical Exercise study (or SHAPE, for short). It 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.
About the study
Funding for the study was provided by the Heart,
Lung and Blood Institute, a member of the National Institutes of Health
(NIH), with additional assistance from the Johns Hopkins Bayview General
Clinical Research Center, also funded by the NIH. Other Hopkins
researchers who took part in this study were Anita Bacher, M.S.N.,
M.P.H.; Paul Hees, Ph.D.; Matthew Tayback, Sc.D.; and Pamela Ouyang,
M.D.
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