In Response: Differing on Vitamin D

January 28, 2011

Why IOM and experts don’t agree on recommended vitamin D levels.

The public was recently treated to a taste of how broad-based public-health recommendations can fall short of where the science stands when the Institute of Medicine (IOM) made its long-awaited announcement this past November updating the Dietary Reference Intakes (DRIs) for calcium and vitamin D for the first time in 13 years. The new recommendations for vitamin D include an Estimated Average Requirement (EAR) for adults of 400 IU/day and a Recommended Dietary Allowance (RDA) for adults of 600 IU/day (800 IU/day for those over 71 years).

While these changes represent a step in the right direction, they still fall short of what widespread research suggests about the importance of vitamin D at higher intake levels. In fact, much of the newer research supports adult intakes up to 2000 IU/day. So, why the disconnect between IOM’s conservative approach versus what many vitamin D experts have been calling for?

The most impactful reason is that the majority of the newer data supporting vitamin D health benefits beyond bone health come from observational studies, which the IOM Committee essentially dismissed, choosing instead to focus on randomized controlled trial (RCT) data. This means that IOM did not consider all of the data on vitamin D and health outcomes, ignoring observational research on the reduction of cardiovascular disease risk, certain cancers, diabetes, and other conditions-research that points to optimal intakes of 1000 to 2000 IU/day. The Committee’s evidence-based medicine approach excluded these important findings that indicate vitamin D at higher levels provides benefit beyond bone health.

The IOM Committee also concluded that the “cutoff” (level below which people are considered insufficient) for blood levels of vitamin D (serum 25-dihydroxyvitamin D3) should be well below that called for by many vitamin D experts. A lower target translates into fewer people being considered insufficient and thus a lesser need for consumption of vitamin D–containing dietary supplements and fortified foods-a point not lost on the consumer media.

Regarding safety, the IOM took a step in the right direction, but remained conservative. Although the Committee doubled the tolerable upper intake level (UL)-defined as a safe intake level above which the risk for adverse effects increases-from 2000 IU/day to 4000 IU/day for adults, its recommendation stood in contrast to the 10,000 IU/day UL suggested by CRN scientists and a group of experts who published two separate, peer-reviewed journal articles supporting their position. This conservative approach was necessary, the Committee argued, due to the lack of long-term RCT data on daily intakes above 2000 IU. The Committee also identified a handful of reports in the literature of slight increases in risk for certain cancers associated with higher blood levels of vitamin D, which added to their conservatism. Ironically, these data were derived from observational studies-the same kinds of studies categorically discounted for demonstrating benefit.

Thankfully, the Committee realized the need to update the recommendations for vitamin D, but we can’t ignore the fact that their recommendations do not reflect the totality of evidence supporting vitamin D as beneficial at higher intakes. The one area on which we do agree with IOM is the need for more research on both health and safety-related outcomes-beyond bone health-and also at higher intakes. The good news is that the National Institutes of Health is preparing to conduct a large-scale (20,000 subjects), long-term trial using vitamin D and omega-3s and assessing a variety of health outcomes.

Moving forward there is also this question to ask: Is there a way to change the scientific framework applied by IOM for future DRIs? When IOM undertakes the process in the coming years for other nutrient recommendations (e.g., omega-3’s EPA and DHA, and choline), will it take the same conservative approach and discount a substantial portion of the evidence? It’s time for the scientific community to recognize that researching the effects of nutrients should not fall solely under a drug-like model.