Effect of vitamin D receptor genotypes on calcium absorption, duodenal vitamin D receptor concentration, and serum 1,25 dihydroxyvitamin D levels in normal women

It is well established that bone mineral density is under strong genetic control. Recently it was reported that the Bsm I restriction fragment length polymorphism of the vitamin D receptor (VDR) gene could account for up to 75% of the genetic variance in bone mineral density. However, the physiological basis for such an effect has not been established. The VDR gene codes for the vitamin D receptor protein which regulates intestinal calcium absorption. In order to assess the biochemical basis we studied the effect of common allelic variation of the VDR gene on intestinal VDR protein concentration, calcium absorption, and serum 1,25 dihydroxyvitamin D (1,25(OH)(2)D). Ninety-two Caucasian women were genotyped for Bsm I and Tag I polymorphism at the VDR gene locus. From these we compared 49 young women aged 25-35 years and 43 elderly women aged 65-83 years, who had all three measurements performed. There were no significant differences in intestinal VDR protein concentration, serum 1,25(OH)(2)D, or radioactive calcium absorption among VDR genotype groups. Therefore, the small intestine does not seem to be a target for VDR gene polymorphism.