ABSTRACT
The purpose of this study was to clarify the interaction between environmental and genetic factors on bone. Using an ultrasound bone densitometer, the stiffness of calcaneus was measured in 52 postmenopausal Japanese women. The VDR gene polymorphism was defined by PCR-RFLP using the endonuclease BsmI. Daily walking steps as a physical activity was measured in these subjects with a pedometer for 7 days and calculated as walking steps per day. Simple regression analysis showed that stiffness was significantly correlated with age, years since menopause, weight, and walking steps. There was no significant association between BsmI VDR genotypes and stiffness. The association between VDR genotypes and stiffness was analyzed in high and low walking steps groups (HW. LW) separated by the mean walking steps in each genotype and we found that VDR genotype had the most significant effect on stiffness (p< 0.01) as indicated by using two-factors (VDR genotypes × walking steps) mixed design analysis of covariance (ANCOVA) with the age, years since menopause and weight as covariates. A significant interaction of VDR genotype with walking steps was also observed (p 0.01) . Stiffness of HW was significantly higher than that of LW in both genotypes (Bb: p<0.01, bb: p<0.05) . Our findings showed that the correlation of walking steps with stiffness by simple regression analysis varied with VDR genotypes, but that the slope in Bb did not differ significantly from that in bb and this result did not change after adjustment for age, years since menopause and weight. From now on, further investigations will be needed to clarify the interaction between VDR genotypes and environmental factors in an effect on stiffness.