Reference Intakes of Vitamin D

Intake reference values for vitamin D and other nutrients are provided in the Dietary Reference Intakes (DRIs) developed by the Food and Nutrition Board (FNB) at the Institute of Medicine of The National Academies (formerly National Academy of Sciences). DRI is the general term for a set of reference values used to plan and assess nutrient intakes of healthy people. These values, which vary by age and gender, include:

• Recommended Dietary Allowance (RDA): average daily level of intake sufficient to meet the nutrient requirements of nearly all (97%-98%) healthy people.
• Adequate Intake (AI): established when evidence is insufficient to develop an RDA and is set at a level assumed to ensure nutritional adequacy.
• Tolerable Upper Intake Level (UL): maximum daily intake unlikely to cause adverse health effects.

The FNB established an AI for vitamin D that represents a daily intake that is sufficient to maintain bone health and normal calcium metabolism in healthy people. AIs for vitamin D are listed in both micrograms (mcg) and International Units (IUs); the biological activity of 1 mcg is equal to 40 IU (Table 2). The AIs for vitamin D are based on the assumption that the vitamin is not synthesized by exposure to sunlight.

Table 2: Adequate Intakes (AIs) for Vitamin D [4]

Age	Males	Females	Pregnancy	Lactation
0-12 months	5 mcg (200 IU)	5 mcg (200 IU)
1-13 years	5 mcg (200 IU)	5 mcg (200 IU)
14-18 years	5 mcg (200 IU)	5 mcg (200 IU)	5 mcg (200 IU)	5 mcg (200 IU)
19-50 years	5 mcg (200 IU)	5 mcg (200 IU)	5 mcg (200 IU)	5 mcg (200 IU)
51-70 years	10 mcg (400 IU)	10 mcg (400 IU)
71+ years	15 mcg (600 IU)	15 mcg (600 IU)

In 2008, the American Academy of Pediatrics (AAP) issued recommended intakes for vitamin D that exceed those of FNB. The AAP recommendations are based on evidence from more recent clinical trials and the history of safe use of 400 IU/day of vitamin D in pediatric and adolescent populations. AAP recommends that exclusively and partially breastfed infants receive supplements of 400 IU/day of vitamin D shortly after birth and continue to receive these supplements until they are weaned and consume ≥1,000 mL/day of vitamin D-fortified formula or whole milk. (All formulas sold in the United States provide ≥400 IU vitamin D₃ per liter, and the majority of vitamin D-only and multivitamin liquid supplements provide 400 IU per serving.) Similarly, all non-breastfed infants ingesting <1,000 mL/day of vitamin D-fortified formula or milk should receive a vitamin D supplement of 400 IU/day. AAP also recommends that older children and adolescents who do not obtain 400 IU/day through vitamin D-fortified milk and foods should take a 400 IU vitamin D supplement daily.

The FNB established an expert committee in 2008 to review the DRIs for vitamin D (and calcium). The current DRIs for this nutrient were established in 1997, and since that time substantial new research has been published to justify a reevaluation of adequate vitamin D intakes for healthy populations. Determinations of DRIs are based on indicators of adequacy or hazard; dose-response curves; health outcomes; life-stage groups; and relations between intakes, biomarkers, and outcomes. For vitamin D, the FNB committee will focus on (1) effects of circulating concentrations of 25(OH)D on health outcomes, (2) effects of vitamin D intakes on circulating 25(OH)D and on health outcomes, and (3) levels of intake associated with adverse effects. The FNB expects to issue its report, updating as appropriate the DRIs for vitamin D and calcium, by May 2010.