Step On it For Bone Health
Weight-bearing and strength-training exercises help build and maintain a strong skeleton.
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.
Because physical activity “kick-starts” the process that makes bones stronger and denser, exercise also is essential in building healthy bones and warding off osteoporosis, a bone-weakening that affects more than 28 million Americans—80 percent or whom are female.
“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.
“One problem with the exercise message is that it’s been too complicated,” notes Cosman, a physican specializing in osteoporosis at the Helen Hayes Hospital in New York. Simply put, she says, the best activities for bone health are:
“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.
In general, the higher the impact, the greater the bone benefit. But high-impact activities—such as running and impact aerobics—also carry a greater risk of injury and may not be appropriate for older or overweight exercisers. Researchers are currently studying how to add bone-building force to lower-impact activities, such as wearing a weighted vest while walking.
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.
While it’s never too late to start exercising for bone benefit, the importance of exercise on skeletal health begins in youth.
“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 musculo-skeletal diseases branch of the National Institute of Arthritis and Musculo-skeletal 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.
Adults who are sedentary and eat poorly may lose bone more rapidly. Studies of patients confined to bed and of astronauts in space reveal that both inactivity and the loss of gravity’s effect on the skeleton can lead to a dramatic loss of bone.
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.”