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information about intakes and serum 25OHD levels consistent with an RDA value than they have for an EAR value.

Data relating bone health outcomes to vitamin D intake are generally limited for adults 19 to 50 years of ages. Although bone mass measures are, of course, studied in this population, consideration of the dose–response relationship between vitamin D and bone health are not usually included in such studies. In fact, there are no randomized trials in this age group, and whatever data are available come from association studies. The results are inconsistent, in part because the confounding inherent in observational studies.

Serum 25OHD concentrations relative to calcium absorption, therefore, provide an important basis for DRI development for vitamin D for these life stage groups. The conclusions described above indicating that calcium absorption is maximal at serum 25OHD concentrations between 30 and 50 nmol/L with no consistent increase in calcium absorption above approximately 50 nmol/L are informative in estimating the relevant EAR and RDA values for vitamin D for these life stage groups.

In contrast, although data from a very recent study (Priemel et al., 2010) based on post-mortem analysis of the relationship between serum 25OHD levels and osteomalacia and re-examined by the committee (as described above) suggest a serum 25OHD level that would cover the needs of approximately 97.5 percent of the population, they also reveal that a level of serum 25OHD consistent with an average requirement is somewhat elusive. That is, serum 25OHD levels of approximately 40 nmol/L to even 30 nmol/L might be expected to be consistent with coverage for no more than half of the population (i.e., a mean/median value). But, in the Priemel et al. (2010) report, even at serum 25OHD levels well below 30 nmol/L more than half of the population studied failed to demonstrate osteomalacia as defined histologically in the study. In essence, these data, which admittedly have limitations, suggest that for some adults the need for vitamin D is extremely low. This is likely due to the very strong interrelationship between calcium and vitamin D; it may even suggest that calcium is the “driver” nutrient relative to bone health, and that calcium is able to more readily overcome lower levels of vitamin D for the purposes of bone health, while vitamin D is likely unable to compensate for a lack of calcium. This finding underscores the uncertainties that are introduced by the calcium-vitamin D interrelationship.

For the purposes of ensuring public health in the face of uncertainty and providing a reference value for stakeholders, a prudent approach is to begin the consideration of the DRIs for these age groups with the level of 25OHD in serum that is consistent with coverage of the requirement of nearly all adults in this age range, that is, 50 nmol/L. Taken together with calcium absorption and BMD, and assuming a normal distribution



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