A new meta-analysis of randomized controlled trials found vitamin D2 supplementation reduced the body’s vitamin D3 levels, with many studies showing D3 falling below control-group levels.
Researchers said that matters because vitamin D3 is the form produced from sunlight and is generally more effective at raising overall vitamin D status than D2.
Earlier Surrey-led research also suggested D3, but not D2, stimulates type I interferon signaling—a first-line immune defense against viruses and bacteria.
The findings are prompting scientists to reconsider whether D3 should be the preferred supplement, as the UK advises 10 micrograms daily and deficiency remains widespread in winter.
Is your vitamin D2 supplement secretly sabotaging your body's natural defenses?
Beyond just taking D3, what crucial cofactors unlock its full immune-boosting power?
If vitamin D2 depletes D3, should all D2-fortified foods be immediately recalled?