Meta-analysis links vitamin D2 to lower D3 levels — ScienceDaily
A meta-analysis conducted by researchers at the University of Surrey, the John Innes Centre and Quadram Institute Bioscience found that taking vitamin D2 may lower blood levels of vitamin D3 — the form the body synthesizes under sunlight. ScienceDaily reports on the findings of the study, published in 2025 in the journal Nutrition Reviews.
The scientists analyzed 20 studies, with data from 11 of them included in the main meta-analysis. In people who received D2, concentrations of 25-hydroxyvitamin D3 were lower than in those who did not take D2. Depending on the analytical method, the average decrease ranged from approximately 9 to 18 nanomoles per liter.
Two forms of one vitamin
Vitamin D2, or ergocalciferol, is usually produced from mushrooms or yeast exposed to ultraviolet light. Vitamin D3, or cholecalciferol, is formed in human skin under ultraviolet B radiation. After entering the body, the liver converts these forms into 25-hydroxyvitamin D — the indicator doctors usually measure in blood to assess vitamin D status.
A decrease in D3 does not mean that D2 does not work or removes all vitamin D from the body. D2 raises levels of 25-hydroxyvitamin D2 and contributes to overall vitamin D status. At the same time, accumulated evidence, including recommendations from the U.S. National Institutes of Health, indicates that D3 is generally more effective at raising vitamin D levels and keeping them elevated for longer.
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The mechanism and health implications are still being studied
Researchers have not yet established why D2 may reduce D3 concentrations. One explanation is that as levels of vitamin D metabolites rise, the body may accelerate their breakdown and excretion. Earlier experiments also suggested the opposite effect: D3 supplements sometimes lowered levels of metabolites derived from D2.
A separate study published in Frontiers in Immunology found differences in the effects of D2 and D3 on gene activity in blood. Unlike D2, D3 was associated with stimulation of type I interferon signaling — an important part of early immune defense. However, the authors stress that changes in gene activity do not prove that D3 can prevent specific infections.
A 2026 systematic review and meta-analysis covering 26 randomized D2 trials also confirmed the biological effect of this form: it lowered parathyroid hormone levels and slightly increased calcium concentrations in the blood. Scientists still need to determine whether the recorded decrease in D3 will have significant long-term health consequences.
