Mild aerobic exercise no protection from osteoporosis

FDA Consumer, Jan-Feb, 2003

While day-to-day physical activities such as walking, housework and shopping may be good for your heart, they don't do much for your bones, researchers at Johns Hopkins University. in Baltimore say.

Their study, published in the November 2002 issue of the Journal of Internal Medicine, found that neither light-intensity activities nor aerobic fitness level contributed to bone health, contrasting previous studies suggesting that aerobics could play a role. Having a few extra pounds, however, was a help. Among a group of older adults studied, those with greater muscle strength and higher body fat, especially in the abdomen, had higher bone mineral densities.

"Carrying extra body weight increases the forces on bone, strengthening it, though the largest forces come from more vigorous exercise rather than routine low-intensity physical activity," says lead author Kerry J. Stewart, Ed. D., director of clinical exercise physiology at Johns Hopkins. "In our study of typical older people, who unfortunately do not participate in regular vigorous exercise, daily activities and low-intensity exercise like walking appeared to be relatively ineffective for preventing aging-related bone loss."

The researchers do not advocate gaining weight to fight osteoporosis.

"Paradoxically, a high percentage of abdominal fat seems to increase bone mineral density," Stewart says, "but it also increases the risk of heart disease, high blood pressure and diabetes, and worsens the symptoms of chronic conditions such as knee arthritis."

Stewart and colleagues studied 84 adults (38 men and 46 women) ages 55 to 75 with higher than normal blood pressure but who were otherwise healthy. They were not exercising regularly, defined as moderate- or high-intensity exercise for 30 minutes a day, three or more times per week.

Researchers used X-rays to measure the participants' bone mineral density in the total skeleton, lower spine and hip, and calculated abdominal fat with magnetic resonance imaging. They weighed each participant and had each do a treadmill exercise test and a series of weight-training exercises to measure aerobic fitness and muscle strength. In addition, the individuals completed a physical activity questionnaire.

The study found that aerobic exercise was not associated with bone mineral density but abdominal fat was. Muscle strength was associated with bone mineral density at some, but not all, sites tested.