Research Finds Vitamin D2 Supplementation Can Reduce Body Levels of Vitamin D3
According to research published in 2025 by scientists from the University of Surrey, John Innes Centre, and Quadram Institute Bioscience, taking vitamin D2 supplements can reduce concentrations of vitamin D3 in the body. While both forms raise overall vitamin D status, evidence indicates D3 is generally more effective at raising and maintaining blood levels. Furthermore, a study led by Professor Colin Smith indicated that vitamin D3 stimulates activity associated with type I interferon signaling in the blood, whereas vitamin D2 does not.
Key points
- A 2025 study published in Nutrition Reviews found that vitamin D2 supplementation is linked to lower concentrations of 25-hydroxyvitamin D3.
- Vitamin D3 is generally more effective than D2 at raising and maintaining overall blood vitamin D levels.
- Research indicates vitamin D3 stimulates type I interferon signaling in the blood, while vitamin D2 does not.
- A separate 2026 systematic review found that D2 supplementation significantly reduced parathyroid hormone levels and slightly increased blood calcium.
What Happened
Research published in 2025 by scientists from the University of Surrey, the John Innes Centre, and Quadram Institute Bioscience examined randomized controlled trials to determine how vitamin D supplements affect the body. The meta-analysis revealed that taking vitamin D2 can lead to significantly lower concentrations of 25-hydroxyvitamin D3, the form produced naturally in human skin or via D3 supplementation.
Emily Brown, a PhD research fellow and lead researcher at the University of Surrey, noted that while vitamin D supplements are important during darker months when sunlight is weak, the finding that D2 decreases D3 levels was previously unknown.
Context
Vitamin D2 and vitamin D3 are frequently treated as interchangeable sources of the same nutrient. However, current U.S. National Institutes of Health guidance notes that D3 tends to raise blood vitamin D levels more and keep them elevated for longer than D2.
Additionally, a study led by Professor Colin Smith at the University of Surrey examined gene activity and found that D3 appeared to stimulate activity associated with type I interferon signaling, which aids the body's early defenses against viruses and bacteria, whereas D2 did not show this effect.
What's Next
Scientists emphasize that further research is required to determine whether these biochemical differences translate into meaningful variations in long-term health outcomes. Additional studies will investigate how D2 and D3 are metabolized and whether D3 should become the preferred form for routine supplementation.
Why it matters
Understanding the metabolic differences between vitamin D2 and vitamin D3 helps clarify which form is more effective for maintaining blood nutrient levels and immune signaling during months when natural sunlight exposure is insufficient.
What we know
- A 2025 study published in Nutrition Reviews found that taking vitamin D2 can reduce levels of vitamin D3 in the body.
- Current U.S. National Institutes of Health guidance states that vitamin D3 raises vitamin D levels more and keeps them elevated for longer than D2.
