Early vertebral trabecular bone loss in normal premenopausal women.

The precise timing for the onset of trabecular bone loss in women is a matter of controversy. To address this issue, we studied the relationship between age and vertebral trabecular bone density (measured by computed tomography) in 74 healthy premenopausal women from 18 to 48 years old. We also measured radial cortical bone density (by single photon absorptiometry) in 28 of these subjects. Trabecular bone density levels (milligrams per milliliter, mean +/- standard error of the mean, SEM) were significantly (p less than 0.05) higher in the second (178 +/- 8) and third (171 +/- 6) decades than in the fourth (158 +/- 4) or fifth (140 +/- 12) decades, and were inversely correlated with age (r = -0.39, p = 0.0006), diminishing at a rate of 1.3 mg/ml (0.73%) per year. Radial cortical bone density levels (grams per square centimeter) were similar in the third (0.711 +/- 0.021), fourth (0.721 +/- 0.012), and fifth (0.736 +/- 0.012) decades and were not related to age (r = 0.17, p = 0.39). We conclude that vertebral trabecular bone loss in women commences during or prior to the third decade. In contrast, radial cortical bone density does not decline during the premenopausal years.