Using new technology, researchers were able to determine that the Recommended Dietary Allowance (RDA) for vitamin D intake is estimated to be 400 International Units (IU) per day rather than 800 IU. The findings of this study were presented at ENDO 2017 in Orlando, FL.

“In estimating the RDA for vitamin D intake, the laboratory method used for measuring 25-hydroxyvitmain D (25[OH]D) can affect the results,” said principal investigator J. Christopher Gallagher, M.D., professor and director of the Bone Metabolism Unit in the Division of Endocrinology of Creighton University School of Medicine in Omaha, Neb. “The estimated RDA based on the older immunoassay (DiaSorin S.p.A., Salugia, Italy) system was 800 IU daily, whereas the newer liquid chromatography tandem-mass spectrometry (LC-MS/MS) technique estimated that 400 IU daily would meet the RDA.”  

To investigate this difference, the researchers looked at an earlier, double-blind, dose-response trial (n=163) in healthy postmenopausal Caucasian women aged 57–90 years with vitamin D insufficiency (serum 25[OH]D ≤20ng/mL) in the winter and spring of 2007–2008. The women were randomized to one of seven vitamin D3 doses: 400, 800, 1600, 2400, 3200, 4000, 4800 IU/day or placebo for one year and were also given calcium supplements. 

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Analysis of the samples using the older immunoassay method found that 800 IU daily would meet the vitamin D requirement in 97.5% of the population. However, when the samples were re-analyzed with the newer LC-MS/MS method, the researchers established a more precise RDA for vitamin D to be 400 IU daily.

Dr. Gallagher concluded, “This has important ramifications for public health recommendations. The amount of vitamin D needed, 400 IU daily, is less than the figure recommended by Institute of Medicine.” The authors cautioned this RDA value was for bone health only and requirements may differ for other conditions. There is no conclusive data on this as trials evaluating cancer, diabetes, and other conditions are ongoing.

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