The Latest Dietary Reference Intakes for Vitamin D

The Institute of Medicine (IOM) released new dietary reference intakes (DRIs) for calcium and vitamin D on November 30, 2010. The IOM concluded that vitamin D plays a key role in bone health and that current evidence does not support other health benefits from vitamin D supplementation, although the IOM called for additional research targeted at other health outcomes to continue. The changes in the recommended dietary allowance (RDA) for vitamin D were based solely on bone health. The IOM raised the RDA in children (1-18 years) and adults (19-70 years) from 200 IU to 600 IU per day and raised the tolerable upper intake level (UL) for adults from 2,000 IU to 4,000 IU per day. For the elderly (>70 years), the RDA was increased to 800 IU per day. The majority of vitamin D experts were disappointed by these conservative increases, but they should be considered steps in the right direction.

The IOM also made another very important change. After reviewing the published literature, they concluded that the serum level of vitamin D sufficient for bone health is above 20 ng/ml rather than 30-32 ng/ml, a value that has been used extensively by physicians. During the press conference, they said that it was warranted by the available scientific evidence even though it had not been one of their tasks. By lowering the sufficient level, they, in effect, reduced the number of people that would be considered to have inadequate serum levels of vitamin D. This change will likely cause significant confusion for both physicians and their patients, but it should be noted that it is only relevant to bone health and may not be optimal for other health benefits that have been attributed to vitamin D.

While the new RDA may bring many people into the new sufficient range, a cut-off of 20 ng/ml is controversial in the vitamin D research community because it does not consider other areas of health that the IOM has concluded are not supported by the currently published data.

The IOM is very conservative and based their decisions on a lack of randomized controlled trials (RCTs) that demonstrate a clear benefit from taking vitamin D supplements beyond bone health, but there is overwhelming evidence that supports biological plausibility for a role of vitamin D in numerous other health outcomes. For example, most non-bone cells have receptors for vitamin D, and we know that the function of immune cells is affected by vitamin D. The IOM narrowly focused on RCTs as the “gold standard”—an almost impossible hurdle to clear when applied to micronutrients. For example, subjects in the placebo group in an RCT will still have some of the micronutrient under evaluation in their bodies—unlike an RCT testing drugs; otherwise, they would get deficiency diseases. While anecdotal reports or single studies seem to be good enough for the IOM to determine the UL, multiple RCTs demonstrating similar outcomes are required for the RDA. Clearly, this is a double standard. DRIs need to take into account the totality of evidence, not just RCTs.

Linus Pauling Institute (LPI) continues to recommend a daily intake of 2,000 IU of vitamin D. This is well below the UL of 4,000 IU set by the IOM and should ensure that individuals, particularly in areas of the world where sun exposure is limited for extended periods of the year, get enough vitamin D. Also, to adjust for individual differences and ensure adequate body vitamin D status, LPI recommends aiming for a serum 25-hydroxyvitamin D level of at least 80 nmol/l (32 ng/ml). You can find this information and the recommendations for infants and children in the LPI Micronutrient Information Center section on vitamin D.

http://lpi.oregonstate.edu/ss11/vitaminD.html