Vitamin D2 or D3? UK studies find differences in how they work
People taking vitamin D2 have lower blood levels of vitamin D3, a meta-analysis finds. Researchers stress D2 is not harmful, but larger studies are needed.
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The two main forms of vitamin D in supplements, D2 and D3, do not appear to work the same way. Researchers at the University of Surrey, the John Innes Centre and the Quadram Institute in Britain have brought together the results of several studies. A systematic review and meta-analysis of randomised trials in the journal Nutrition Reviews screened 20 studies, 11 of which were included in the main analysis. People taking vitamin D2 had significantly lower blood levels of 25-hydroxyvitamin D3 – by roughly 9 to 18 nmol/L on average, depending on the analysis.
A second study led by Colin Smith and published in Frontiers in Immunology examined how the two forms change gene activity in the blood. It found that D3, but not D2, appeared to stimulate type I interferon signalling, an early immune defence against viruses and bacteria. A third meta-analysis of 26 trials shows that D2 also has measurable effects: it lowers parathyroid hormone and slightly raises blood calcium.
"Vitamin D3 supplements may be more beneficial for most individuals over vitamin D2," said lead researcher Emily Brown. The researchers stress, however, that lower D3 levels do not mean D2 is harmful or ineffective, and the immune findings do not prove that D3 prevents infections. Larger clinical studies are needed.
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