Age and sex differences in the bone mineral density of the distal forearm based on health check-up data of 6343 Japanese.

Bone mineral density (BMD) predicts osteoporotic fractures. The incidence of osteoporotic fractures in Japan is lower than among Caucasians, but fewer data on the BMD of Asians have been reported. This study attempted to clarify the age and sex differences in the forearm BMD of healthy adult Japanese and to assess racial differences between Japanese and Caucasians. The subjects were 6343 healthy adult Japanese (5281 females, 1062 males) who underwent a health check-up at a health care service center between February 1995 and August 1999. Subjects' age ranged from 15 to 80 years. The BMD of the distal radius and ulna of the non dominant forearm was measured by dual-energy X-ray absorptiometry. Overall, the forearm BMD of men was greater than that of women in all age groups. Peak BMD was 0.484 g/cm2 in the 40-44 year age group of women and 0.590 g/cm2 in the 30-34 year age group of men. The forearm BMD of women under 50 years of age (the average age at menopause) increased slightly with age (2.0%/decade, p < 0.0001), but it did not among their male counterparts. After 50 years of age, BMD of the women decreased linearly (-1.6%/year, p < 0.0001) with age, the rate of decrease being 1.7-fold faster than in their male counterparts. Rates of gain and loss of forearm BMD differ between the sexes. In comparison with data previously reported, we did not find any evidence of racial differences in BMD as an explanation for the lower incidence of osteoporotic fractures in Japan.