A new meta-analysis from the University of Surrey found that taking vitamin D2 supplements can actually reduce the body's levels of vitamin D3 — the form naturally produced from sunlight and considered more effective at raising overall vitamin D status. Researchers analyzed data from multiple randomized controlled trials and found D3 levels often dropped below those seen in control groups not taking any supplement. Separate research also shows D3 uniquely activates type I interferon signaling, a frontline immune defense against viruses and bacteria — an effect D2 does not appear to share. Scientists are now urging a rethink of supplement recommendations, suggesting D3 should be the preferred choice for most people, with plant-based D3 options made more widely available for those avoiding animal-derived products.
