Vitamin D2 supplements may quietly lower the body's vitamin D3 levels, meta-analysis finds

A new meta-analysis in Nutrition Reviews finds vitamin D2 supplements can actually reduce the body's vitamin D3 levels by about 18 nmol per liter. In some cases D3 fell below the level seen in people taking no supplement at all. The authors now recommend prioritising vitamin D3.

A new systematic review and meta-analysis in Nutrition Reviews pooled 11 randomized controlled trials covering 655 adults and found vitamin D2 supplementation cuts blood D3 by about 18 nmol per liter, sometimes below levels in people taking no supplement at all. Both forms are sold as vitamin D but are not interchangeable in the body. The authors recommend prioritising D3. Check the label: ergocalciferol is D2, cholecalciferol is D3.

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