Quadriceps and grip strength are related to vitamin D receptor genotype in elderly nonobese women

Abstract

Osteoporotic fragility fractures are related to bone density and injury, which are both related to muscle strength. The influence of genetic factors, such as the vitamin D receptor (VDR) polymorphism on bone mineral density (BMD), is documented but still controversial, and is not known for muscle strength. In the present study, we investigated the association between the VDR BsmI polymorphism and BMD (femoral neck [FN], lumbar spine [LS], and proximal forearm [FA]) and muscle strength (quadriceps and grip strength) in 501 healthy women older than 70 years. No association was found between the VDR genotypes and BMD in elderly women. However, in nonobese women (body mass index <30 kg/cm2), the BMD in the FN was 5% higher in women with the bb BsmI genotype than in women with the BB genotype (p < 0.05). After correction for muscle strength, no association was found. A significant association between the VDR genotypes and quadriceps and grip strength was observed. In nonobese women, a 23% difference in quadriceps strength (p < 0.01) and 7% in grip strength (NS) was observed between the bb and BB genotype of the VDR. After correction for confounding factors and BMD, this association was significant for quadriceps and grip strength. These results indicate a major association of an allelic variant at the VDR locus with muscle strength in elderly nonobese women, which could explain a small association between VDR polymorphism with BMD in the femoral neck in nonobese women. No such associations were found in obese women, suggesting that factors related to obesity obscure such an association.