Japanese fermented soybeans (natto in Japanese), which contain a large amount of menaquinone-7, may help prevent the development of osteoporosis. We assessed the possibility of an association between habitual natto intake and bone mineral density (BMD) and BMD change over time in healthy Japanese women who participated in a large representative cohort study (Japanese Population-based Osteoporosis Study: JPOS study). The BMD was measured at the spine, hip, and forearm in 944 women (20–79 y old) at baseline and at a follow-up conducted 3 y later. Dietary natto intake was assessed by a FFQ on both occasions. Additional covariates including age, height, weight, lifestyle factors, dietary calcium intake, and the intake of other soybean products, were also measured. The total hip BMD at baseline increased (P for trend = 0.0034) with increasing habitual natto intake in the postmenopausal women, although this was not the case at other skeletal sites. There were significant positive associations between natto intake and the rates of changes in BMD at the femoral neck (P < 0.0001) and at the distal third of the radius (P = 0.0002) in the postmenopausal women. The association in the femoral neck persisted even after adjusting for covariates. No significant association was observed between the intake of tofu or other soybean products and the rate of BMD change in the postmenopausal women. Natto intake may help prevent postmenopausal bone loss through the effects of menaquinone 7 or bioavailable isoflavones, which are more abundant in natto than in other soybean products.

Background Vitamin D receptor (VDR) gene polymorphisms have been inconsistently associated with bone mineral density (BMD). To precisely evaluate the associations between three VDR gene polymorphisms and BMD, we performed a large-scale representative study of the Japanese female population. Methods Fifty women were randomly selected from each of the 5-year age stratified populations (15–79 years) in each of the three municipalities examined, as a part of the Japanese population-based osteoporosis (JPOS) baseline study in 1996. In the study, BMD at the lumbar spine, hip, and distal forearm were measured using dual energy X-ray absorptiometry (DXA). Two polymorphisms were determined in the VDR gene locus identified by the restriction endonucleases ApaI and TaqI through a novel allele discrimination method using two different allele-specific fluorescence probes. The other VDR gene polymorphism was identified by the restriction endonuclease FokI using the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method. Changes in BMD were determined in a follow-up study 3 years after the baseline study. Results After the exclusion of women who had any medical or menstrual history affecting BMD, 1434 women were analysed. The annual per cent changes in BMD at the lumbar spine over 3 years in subjects with tt genotype in the TaqI polymorphism were different from other genotypes, both in the women who were premenopausal at the follow-up survey (F-premenopausal women) and in the women who were postmenopausal at the baseline survey (B-postmenopausal women). However, the effects of tt genotype on change in BMD were opposite in the two groups. In addition, these associations or tendencies were not observed at the different skeletal sites. Conclusions This study revealed that none of the individual VDR gene polymorphisms displayed consistent association with baseline BMD or BMD change. Therefore, the effect of the VDR genotype on bone mass is negligible in Japanese women.