Exercise-associated cancellous bone change: Positive effect of ovulation 1116

Current concepts suggest that normal estrogen levels are necessary for exercise to have an osteogenic effect on bone. In a population of running and sedentary women Prior et al. (NEJM, 1990) have shown that consistent ovulation is necessary to prevent spinal cancellous bone loss. Change in spinal bone mineral density was measured by quantitative computed tomography (QCT) in running and sedentary women over one year, along with prospective documentation of dietary, menstrual cycle, hormonal, and exercise variables. Of the 66 women studied only 12 remained ovulatory throughout the year. Forty-two women were runners of which 6 were consistently ovulatory. We hypothesized that ovulation would interact with an exercise effect on cancellous bone. Analysis of the 42 runners showed an average loss in bone of 1.8%. Luteal phase index (r = 0.509) and average progesterone (r = 0.381) were correlated with change in QCT, but not estrogen, calcium, or any other hormonal, dietary, or morphometric variable. There was a negative association between change in QCT and number of km run/week (r = -0.319). In the 12 consistently ovulatory women, average cancellous bone increased in runners(≈2%) and decreased in nonrunners (N) by ≈1% (seefig.). These data are the first to show an increase in purely cancellous bone with moderate levels of aerobic activity. The results suggest that the presence of consistently ovulatory cycles, and thus progesterone in addition to estrogen, may be necessary for an osteogenic effect of low impact exercise (running) on cancellous bone.