What are the dietary requirements for calcium and vitamin D?

Dietary recommendations for calcium and vitamin D vary considerably among different advisory bodies. This lack of consensus reflects the different criteria used as a basis for estimating average requirements and population reference values. For calcium (Ca) many have used a factorial approach, where estimates of skeletal accretion rates are coupled with assumptions about Ca absorption and excretion on typical diets. Others have used data derived experimentally from balance studies. A recent refinement of this approach involves the mathematical modelling of balance data to estimate a Ca intake above which Ca retention is maximal or desirable. A third approach was used by a NIH Consensus Conference in 1994, based on the concept of an optimal Ca intake for bone health, in terms of reduced risk of osteoporosis in later life. Although taken up by several special-interest groups, this approach has yet to be adopted fully by any committee advising on nutrition policy because of the lack of quantitative data on which to base estimates of average calcium requirements. Differences in vitamin D recommendations reflect subtle differences in philosophy about how to indicate that while endogenous synthesis is the main source of vitamin D for people with adequate sunshine exposure, there are vulnerable groups that rely on the diet to supply their vitamin D requirements. In addition, they reflect uncertainties about the relationship between vitamin D status and health outcomes.