Bone mineral density, carotid artery intimal medial thickness, and the vitamin D receptor BsmI polymorphism in Mexican American women

Low bone mineral density (BMD) is a predictor of cardiovascular mortality, suggesting that osteoporosis and cardiovascular disease may share common risk factors. We assessed the relationship between BMD and intimal medial thickening (IMT) of the common carotid artery, a marker of sub-clinical atherosclerosis, in 471 women examined as part of the San Antonio Family Osteoporosis Study, a population-based study of osteoporosis risk conducted in Mexican American families. Because of the documented role of vitamin D metabolism in bone metabolism and its possible role in cardiovascular function, we further evaluated whether allelic variation at the vitamin D receptor locus (VDR) influenced joint variation in BMD and IMT. The association of BMD with IMT depended on age, with low BMD being correlated with high IMT in older women, but with low IMT in younger women [age by IMT interaction effects significant at the spine (P = 0.042), radius ultradistal (P = 0.010), and hip (P = 0.006)]. In all women, the VDR BsmI BB genotype was associated with significantly higher forearm BMD (P = 0.005 for both radius ultradistal and midpoint), higher IMT (P = 0.05), and higher spine BMD in older women (P = 0.06), but not with hip BMD. The association of the VDR genotype with IMT was independent of its association with BMD. Although a functional consequence of the BsmI polymorphism on vitamin D metabolism has not been established, these findings support a possible biological relationship among VDR, bone metabolism, and atherosclerosis. We conclude that VDR polymorphisms may be one of multiple factors influencing the joint risk of atherosclerosis and osteoporosis.