Overview

• A peer-reviewed review in Nutrition Reviews pooled randomized controlled trials and found that taking vitamin D2 was frequently linked to lower circulating 25-hydroxyvitamin D3.
• In many included trials, participants given D2 recorded lower D3 levels than those in placebo or control groups.
• Study authors stressed that D2 still raises total vitamin D and is not dangerous, and they reiterated the importance of winter supplementation where sunlight is insufficient.
• Cited prior research indicates functional differences for immunity, with D3—unlike D2—stimulating type I interferon signaling.
• The team called for wider access to plant-based D3 and for mechanistic and outcomes-focused studies to guide supplementation and fortification choices.