of requirements, given no evidence that the distribution is not normal, a serum level of 40 nmol/L can be set as consistent with a median requirement. This modified approach is bolstered by—and consistent with—the relationship between serum 25OHD levels and calcium absorption, in which serum 25OHD levels of between 30 and 50 nmol/L were consistent with maximal calcium absorption. Based on these considerations as well as the intake versus serum response analysis described above, an EAR of 400 IU/day and an RDA of 600 IU/day are established for adults 19 to 50 years of age. These DRI values assume minimal sun exposure.
For persons in these life stage groups of 51 through 70 years and >70 years, the ability to maintain bone mass and reduce the level of bone loss is the primary focus for DRI development. Evidence related to fracture risk becomes central. For this reason, DRIs for adults >70 years of age are discussed first, followed by DRIs for adults 51 through 70 years of age.
The discussions above concerning serum 25OHD levels in relation to bone health indicate that several newer studies have helped to elucidate a relationship between serum 25OHD concentrations and bone health benefits based on measures of calcium absorption and osteomalacia for a wide age range of adults. These data when used for the purposes of DRI development—coupled with the approximation of intake associated with serum 25OHD concentrations derived from the simulation analysis carried out by the committee—provide a basis for an EAR for young and middle-aged adults of 400 IU/day vitamin D consistent with a serum 25OHD concentration of 40 nmol/L, and for an RDA of 600 IU/day consistent with a serum 25OHD concentration of 50 nmol/L. However, for adults more than 70 years of age, the number of unknowns associated with the physiology of normal aging, coupled with the level of variability around the average requirement for this group that such factors may introduce, all of which may affect the estimation of the RDA (the level of intake needed to cover