Age-related loss of bone mineral density in non-athletic and athletic women.

Single and dual photon absorptiometry were performed at the mid-radius, distal radius and lumbar spine in 1105 non-athletic and 124 athletic Caucasian women aged 18-98 years. An age-related loss of bone mineral density in mg/cm2 (BMD) occurred at the three skeletal sites. It was first demonstrated that a single break in the regression line (BMD versus Age) best fit the data. The break represented the approximate age at which an increase in the rate of bone density loss occurred. This break is termed the 'cutpoint'. The approximate (average) age at which the cutpoint occurred was determined by segmented regression analysis with bone density as the dependent variable. The age range studied was between 45 and 55 years. At all three bone sites, the cutpoints in non-athletic women occurred between 47 and 52 years of age, corresponding roughly to the time of menopause. Following this cutpoint the rate of bone loss increased at all three locations in non-athletic women. In athletic women no cutpoint in BMD values could be demonstrated for this age range for the two radial sites. The number of lumbar spine measurements in this group was too small for analysis. The absence of a significant change in rate of bone loss in athletes could have been due to the relatively small number of subjects. It could also suggest that regular sustained exercise programs may delay or minimize the increased rate of loss of BMD which occurs in non-athletic women in the perimenopausal period.