Aerobic Fitness and Body Mass Protect Against Bone Loss in Healthy Midlife Women

Abstract

Skeletal bone mass in women begins to decline at about the age of 30 years, and loss accelerates in the immediate postmenopausal years. A longitudinal study of 169 healthy women aged 35–62 years was conducted to determine the combined effects of physical activity and several other factors (age, menopause, race, body mass) on lumbar bone mineral density and change in lumbar bone over 24 months. Lumbar bone mineral content was assessed by dual-energy x-ray bone densitometry. Physical activity was quantified from both a fitness measure of predicted maximum oxygen intake and a retrospective 12-month self-report of time spent in aerobic weight-bearing activities. Fit midlife women, as measured by predicted maximum oxygen uptake, had significantly lower bone mineral density, partly associated with low body mass. On the other hand, the fit women and women with higher body mass had less bone loss over a 2-year period. These data suggest that increased levels of aerobic fitness as well as body mass may prevent some of the bone loss that occurs in healthy midlife women.