A new meta-analysis reveals that vitamin D2 supplements can significantly lower the body’s preferred form, vitamin D3, potentially compromising immune function. Scientists now urge a re-evaluation of supplement choices.
October 4, 2025
Source:
ScienceDaily
Key Findings on Supplement Interaction
Recent scientific analyses have uncovered a critical mistake many are making with vitamin D supplementation. Taking vitamin D2 supplements can actively lower levels of vitamin D3, the body's most effective form for immune support.
A meta-analysis of 11 randomized controlled trials, conducted by researchers at the University of Surrey and other institutions, revealed this previously unknown effect. The findings raise urgent questions about which supplement is best for public health.
D2 Reduces D3 Levels
The research demonstrated that vitamin D2 supplementation not only fails to raise D3 but actively reduces its concentration in the bloodstream. In some cases, D3 levels in those taking D2 dropped below those of control groups taking no supplement at all.
Impact on the Immune System
This discovery has significant implications for immunity. According to the studies, only vitamin D3 (cholecalciferol) appears to trigger the type-I interferon system—an essential first-line defense against viral and bacterial infections. Vitamin D2 (ergocalciferol) does not produce the same protective response.
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Source:
SciTechDaily
Scientific Context and Supplement Forms
For years, vitamin D2 and D3 were considered largely interchangeable for correcting vitamin D deficiency. This new evidence overturns that assumption, highlighting distinct biological outcomes.
A Previously Unknown Effect
Professor Susan Lanham-New, a co-author of the study, noted the significance of the findings. "The reduction of vitamin D3 by D2 supplementation was a surprising discovery," she stated. The precise mechanism is still under investigation but may be linked to how the body metabolizes the two different forms.
Differentiating D2 and D3
Understanding the sources of each form is crucial for making informed choices:
Vitamin D3 (cholecalciferol): This is the form naturally produced in the skin when exposed to sunlight. It is also found in animal-based foods and is considered more potent and effective at raising overall vitamin D levels.
Vitamin D2 (ergocalciferol): This form is derived from plant sources, like mushrooms, and is often used in fortified foods and supplements suitable for vegans.
While both can increase vitamin D status, their impact on the immune system is not equal. More information on vitamin D sources can be found at the National Institutes of Health (NIH).
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Source:
Dr. Jockers
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