In a recent study, researchers re-measured vitamin D with improved technology.
They suggest that the Recommended Dietary Allowance (RDA) for vitamin D intake can drop from 800 to 400 International Units (IU) per day.
In the study, the researchers enrolled 163 healthy postmenopausal Caucasian women 57 through 90 years of age with vitamin D insufficiency and followed them for 1 year.
The women were at least 7 years postmenopausal and they had vitamin D insufficiency based on the World Health Organization cutoff (serum 25(OH)D 20 ng/ml or lower).
The participants were randomized to one of seven vitamin D3 doses: 400, 800, 1600, 2400, 3200, 4000, 4800 IU/day or placebo, for 1 year, and all the women were given calcium supplements to maintain a total calcium intake.
After analyzing the samples and estimating the RDA using the older immunoassay, the researchers found that that 800 IU daily would meet the vitamin D intake requirement for 97.5% of the population.
But now that liquid chromatography mass spectrometry (LC-MS/MS) has become the gold standard for measuring 25(OH)D, the researchers reanalyzed the original samples using this new technology.
Able to determine a more precise dose-response curve, they have calculated the RDA for vitamin D to be 400 IU daily.
The researchers suggest that the RDA is easily achievable with a supplement of 400 IU in winter, when vitamin D levels are lowest in North America.
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 team also cautions that this RDA is for bone health only.
It may be different for other diseases. Although trials looking into cancer, diabetes, and other diseases are ongoing, the researchers do not have information about this now.
The principal investigator is J. Christopher Gallagher, M.D.
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Source reference: The Endocrine Society.