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Starting Early With Bone Density Protection

May 29, 2000|CAROL KRUCOFF | SPECIAL TO THE TIMES

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 condition that affects more than 28 million Americans, 80% of them 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% of adults engage in the recommended 30 minutes of activity most days of the week, says Felicia Cosman, clinical director of the National Osteoporosis Foundation, 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," says Cosman, a physician specializing in osteoporosis at the Helen Hayes Hospital in New York. Simply put, she says, the best activities for bone health are:

Weight-bearing exercises: "This is any activity you do on your feet, that works your bones and muscles against gravity," Cosman says. Walking, jogging, dancing and working in the yard are all weight-bearing 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.

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 Assn., showed that post-menopausal women who performed two 40-minute strength training sessions a week for a year gained 1% in bone density--comparable with the bone benefit of hormone replacement therapy. Women in a sedentary control group lost about 2%.

Although it's never too late to start exercising for bone benefit, the importance of exercise in 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," says 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 arm has about 3% more bone than their nondominant arm, 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% more bone in their dominant arm than in their nondominant arm, while those who started playing before puberty had dominant arms with about 23% 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 unhealthful 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 has called attention to this problem, identifying it as "The Female Athlete Triad: Disordered Eating, Amenorrhea and Osteoporosis." 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 years for making deposits. 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.

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