Vitamin D Receptor Alleles and Bone's Response to Physical Activity

Abstract.

The objective of this prospective controlled study was to determine whether the osteogenic response of bone to mechanical loading is dependent on the vitamin D receptor (VDR) polymorphism. Thirty-five healthy premenopausal women took part in a progressive, high-impact exercise three times a week for a period of 18 months and 45 women served as nonexercising controls. The trainees were divided into three groups: bb (n = 12, 34%); Bb (n = 16, 46%); BB (n = 7, 20%) according to polymorphism at the gene encoding the VDR (BB representing subjects without the restriction enzyme BsmI sites on the two VDR gene alleles). Bone mineral content (BMC) and areal bone mineral density (BMD) were measured at the lumber spine, proximal femur, knee, calcaneus, and dominant distal radius before the beginning of the exercise regimen and at 12 and 18 months of training using dual-energy x-ray absorptiometry (DXA). As an indicator of the total osteogenic effect of the training, ΣBMC was derived by summing up the BMC values of the loaded sites (i.e., the lower limb sites and the lumbar spine). The mean ΣBMC increased 2.0% in the bb group, 3.0% in the Bb group, and 2.8% in the BB group (P= 0.184 for the intergroup difference), but only 0.8% in the controls (exercisers versus controls, P < 0.001). Individuals with the BB genotype of the VDR gene, subjects with whom the BMC can be lower than normal and whose bones can be less responsive to pharmacological therapies than bones of the other individuals, seem to have as good osteogenic response to mechanical loading as subjects with other VDR genotypes. Thus, irrespective of the VDR genotype, physical activity seems to be beneficial for bones of premenopausal women.