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 from 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<0.001) and the metabolite 25OHD₃ (r=-0.41, P<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.