The target population of interest for the reference values are the people residing in the United States and Canada, including those whose needs for or sensitivity to vitamin D or calcium may be affected by particular conditions such as obesity or oral contraceptive use; those with highly pigmented skin; those with risk factors for chronic disease; and those with chronic or other diseases that do not alter their requirements for or sensitivity to vitamin D or calcium. For vitamin D, the target population may also include subgroups within the general population whose requirements for vitamin D intakes may need to be considered within the context of limited endogenous synthesis or differences in metabolic handling of vitamin D (e.g., limited sun exposure because of latitude, clothing, institutionalization, dark skin pigmentation; older persons with reduced capacity for dermal synthesis; racial/ethnic differences in metabolic handling of these nutrients). In deriving the reference values, it is useful if the relevance of study populations found in the literature is considered relative to the target population. It is also important to identify as data allow the special populations whose nutrient requirements or sensitivities differ from the general population as described above for whom DRI values are derived (e.g., diseased persons, persons using drugs known to alter the nutrient requirements or safety profiles).