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Step On it For Bone Health |
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Step On
it For Bone Health
Celebrities with milk
mustaches and the growing number of foods enriched with calcium have
helped boost public awareness that good nutrition is vital to healthy
bones. But calcium and vitamin D are just part of the picture when it
comes to strengthening the skeleton and preventing bone loss with age. “Physical activity, through its load-bearing effect on the skeleton, is likely the single most important influence on bone density and architecture,” concludes the U.S. Surgeon General’s Report on Physical Activity and Health.
Still, only 15 percent of
adults engage in the recommended 30 minutes of activity most days of
the week, notes Felicia Cosman, clinical director of the National
Osteoporosis Foundation (NOF), which has launched a campaign called
“Step On It America!” to encourage people of all ages to get moving
for bone health.
“This is any activity you
do on your feet that works your bones and muscles against gravity,”
says Cosman. Walking, jogging, dancing, and yard work are all
weight-beating activities, while swimming and cycling are not. Strength-training exercises
Working against
resistance, such as by exercising with free weights or
strength-training machines, strengthens both muscles and bones. A
study by Tufts University physiologist Miriam Nelson, published in the
Journal of the American Medical Association, showed that
postmenopausal women who performed just two 40-minute
strength-training sessions a week for a year gained one percent in
bone density—comparable to the bone benefit of hormone-replacement
therapy. Women in the sedentary control group lost about two percent. “Thirty percent of the skeleton can be formed during puberty, which for most girls and boys is between the ages of 9 and 14,” notes Joan McGowan, chief of the musculoskeletal diseases branch of the National Institute of Arthritis and Musculoskeletal and Skin Diseases. “Adolescence provides an incredible opportunity to lay down the mass and shape of bone and to see the influence of exercise.” To illustrate her point, McGowan notes that most people’s dominant arms have about 3 percent more bone than their nondominant arms, because the preferred arm experiences more bone-building force. A Finnish study of elite tennis players found that those who started playing tennis after puberty had 11 percent more bone in their dominant arms than in their nondominant arms, while those who started playing before puberty had dominant arms with about 23 percent more bone. Unfortunately, many youngsters—especially girls—become less active during adolescence. In addition, an alarming number of girls and young women who do stay active engage in unhealthy weight-control practices that can lead to irregular or stopped menstrual periods, which can cause them to lose bone tissue. The American College of Sports Medicine (ACSM) has called attention to this problem, identifying it as “The Female Athlete Triad: Disordered Eating, Amenorrhea, and Osteoporosis.” ACSM experts advise parents and coaches to encourage female athletes concerned about their weight to seek assistance from a qualified sports nutritionist or other health professional.
Although many people
consider osteoporosis to be “a little old lady disease,” experts are
increasingly calling the condition a pediatric disease with a
geriatric outcome. The human skeleton is like a bank account, where
childhood, adolescence, and early adulthood are the major deposit
years. The bone bank’s withdrawal period typically begins after age
30. Until about age 50, bone loss occurs at a relatively slow rate of
about half a percent per year in most people. In women, the decline in estrogen at menopause can hasten bone loss, with some women losing up to 20 percent of their bone mass in the five to eight years after monthly cycles stop. Hormone replacement therapy or other “antiresorptive” medications can be particularly effective at this time in protecting against bone loss, say experts who encourage women at high risk for osteoporosis to get a bone-density test at menopause. While exercise is not a substitute for medications at this time, it is still helpful to continue with weight-bearing and muscle-building exercises. Postmenopausal women who have been sedentary can gain the most benefit from strength training two or three times a week, contends Tufts University’s Nelson. “Strength training exerts high forces without high impact,” says Nelson, who also advises older women to walk briskly, stretch regularly, and do balance exercises. “Balance training doesn’t increase bone density,” she says, “but it can protect whatever bone we have by preventing falls.” |
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