Dietary soybeans intake and bone mineral density among 995 middle-aged women in Yokohama.

To investigate relationship of dietary factors, especially source of calcium intake, to bone mineral density (BMD) among Japanese middle-aged women, a total of 995 healthy women age of 40 to 49 (mean +/- SD, 45 +/- 3), who lives in Yokohama-city, were recruited through convenience sampling by the municipal information paper and health announcement at each 18 public health center in 18 wards for the three-day course on prevention of osteoporosis from October 1996 to March 1998. The BMD of the 2nd metacarpal bone was measured using Computed X-ray Densitometry (CXD) method, by a trained radiologist. Dietary intake of calcium was assessed by self-reporting food frequency questionnaire on calcium dietary sources such as milk, dairy products, small fish, vegetables, and soybeans and carefully checked by trained dietician. An independent gradient of non-adjusted and adjusted BMD for age and weekly calcium intake, through soybeans intake frequency (p = 0.03) was noted. This study suggest soybeans, through possible beneficial effects of vitamin-K, soyprotein, and isoflavonoid, may affect BMD of middle aged women.