Effect of aging on vitamin D stores and bone density in women

It has been suggested that the decrease in vitamin D stores with aging is a contributory cause of age-related osteoporosis. We studied this question by measuring bone mineral density (BMD) of the mid-radius, distal radius, and lumbar spine assessed by single and dual photon absorptiometry in 122 women, aged 33-94 years, selected from a random sample of Rochester, MN residents. We measured serum 25-hydroxyvitamin D (25OHD), the major storage form of vitamin D, as well as 25OHD3 (representing both endogenous and exogenous sources of vitamin D), and 25OHD2 (representing only exogenous sources). Both baseline serum total 25OHD (r = -0.29, P less than 0.001) and the metabolite 25OHD3 (r = -0.41, P less than 0.001), were negatively associated with age at baseline. After adjusting for the effect of age by multiple regression analysis, there was no association between serum levels of 25OHD2, 25OHD3, or total 25OHD and BMD for any of the three skeletal scanning sites. Thus, in a northern American population we cannot demonstrate that reduced bioavailability of vitamin D plays a major role in age-related bone loss.