Triennial Growth Symposium--Basis for establishment of 2011 vitamin D guidelines in humans

The 2011 vitamin D recommendations set by the Food and Nutrition Board of the Institute of Medicine was the first time that Estimated Average Requirements (EAR) and Recommended Dietary Allowance (RDA) were given for vitamin D. Previous versions (i.e., 1997 and earlier) used Adequate Intakes, implying less certainty of evidence to determine the EAR. It is difficult to set requirements for vitamin D because it behaves more like a hormone than a nutrient and because diet is not the only source of vitamin D. In fact, more vitamin D comes from cutaneous production than from diet for most people. Therefore, one cannot use the common factorial approach of estimating daily losses adjusted by absorption and needs during growth to set intake recommendations. The basis for the 2011 vitamin D recommendations was for bone health. Systematic reviews showed vitamin D status levels associated with calcium absorption, bone mineral density, and risk of osteomalacia or rickets. An integrated model was used to set vitamin D status, measured by serum 25-hydroxyvitamin D (25(OH)D) levels, at 40 nM for the EAR and 50 nM for the RDA. Vitamin D intakes to achieve these levels became the recommended intakes based on a nonlinear model of the relationship of vitamin D intake and achieved serum 25(OH)D levels. The panel assumed all vitamin D intakes should come from diet in their recommendations because many groups are not exposed to UVB light, are elderly or are dark skinned, which limits cutaneous production. However, intakes are well below recommended levels. Clinical guidelines for patients at risk for vitamin D deficiency were also established in 2011 by the Endocrine Society, which gives physicians more latitude for vitamin D recommendations.