IOM Responds to Challenge of It's Vitamin D Recommendations by Academics

23 Mar 2015 --- The Institute of Medicine (IOM) has responded to academics who last week challenged its vitamin D intake recommendations, saying that the current recommended Dietary Allowance (RDA) underestimates requirements and were conceived using analysis that included a calculation error.

The IOM’s guidance, published in 2010, states that the average person requires 600IU of the vitamin, which is best absorbed by the body from the sun, while researchers say that a more realistic figure is around 8,000 IU.

The IOM states that the Recommended Dietary Allowance (RDA), by definition, meets the requirements of 97.5 percent of the population. It is set from an Estimated Average Requirement (EAR) that represents an intake amount that will meet the needs of about 50% of the population.  The RDA represents an intake amount that is 2 standard deviations above the EAR. What this means for vitamin D is that for most of the population, their requirements are met by an intake level that will achieve a serum level of the biomarker of vitamin D status, 25(OH)D of 50 nmol/L (equal to 20 ng/mL), determined to be equivalent to an RDA level of vitamin D intake (based on essentially all vitamin D from diet and minimal sunlight exposure).

In its analysis, the IOM committee used a mixed-model approach to estimate the dose-relationship between total dietary intake of vitamin D to achieve the desired serum level of 25(OH)D. In its methodology to determine DRIs for vitamin D, the IOM committee used an estimated dose-response to inform their judgment of the intake needed to achieve serum 25(OH)D levels in the desired range.  Because of limitations in the available data, the IOM committee made the judgment to overestimate the dose of dietary vitamin D needed; 600 IU daily would meet the RDA based on a serum 25(OH)D level of 50 nmol/L derived from the estimated dose-response relationship.

In this approach, the Estimated Average Requirement was determined to be equivalent to an intake that produced a serum level of 40 nmol/L (based on essentially all vitamin D from diet and minimal sunlight exposure).  Thus, because this level represents the RDA for dietary vitamin D, the 2 standard deviations has, in effect, already been added and therefore no additional adjustment is required or appropriate.  

Using the distribution to 97.5 percent to assure a low prevalence of inadequacy among the healthy population groups, the RDA value was based on an achieved level of 50 nmol/L (equal to 20 ng/mL).  To be clear, the goal is not, and should not be, to assure that 97.5% of  the population exceeds the serum value linked to the RDA.  Doing so would shift the distribution to a higher level that is associated with increased risk for adverse effects.

The Tolerable Upper Level (UL) is another Dietary Reference Intake (DRI) value that represents the highest level of daily nutrient intake that is likely to pose no risk of adverse health effects to most individuals in a population. Based on the committee’s review of the evidence, the UL is 4,000 IU/day.  An intake level above 4,000 IU daily exceeds the UL for all age and sex groups.

However, in a letter published last week in the journal Nutrients scientists confirmed a calculation error noted by other investigators, by using a data set from a different population. Dr. Cedric F. Garland, Dr.P.H., adjunct professor at UC San Diego’s Department of Family Medicine and Public Health said his group was able to confirm findings published by Dr. Paul Veugelers from the University of Alberta School of Public Health that were reported last October in the same journal.

“Both these studies suggest that the IOM underestimated the requirement substantially,” said Garland. “The error has broad implications for public health regarding disease prevention and achieving the stated goal of ensuring that the whole population has enough vitamin D to maintain bone health.”

The recommended intake of vitamin D specified by the IOM is 600 IU/day through age 70 years, and 800 IU/day for older ages. “Calculations by us and other researchers have shown that these doses are only about one-tenth those needed to cut incidence of diseases related to vitamin D deficiency,” Garland explained.

Robert Heaney, M.D., of Creighton University wrote: "We call for the NAS-IOM and all public health authorities concerned with transmitting accurate nutritional information to the public to designate, as the RDA, a value of approximately 7,000 IU/day from all sources.”

“This intake is well below the upper level intake specified by IOM as safe for teens and adults, 10,000 IU/day,” Garland said. Other authors were C. Baggerly and C. French, of GrassrootsHealth, a voluntary organization in San Diego CA, and E.D. Gorham, Ph.D., of UC San Diego.