Plate Nº 32 · recorded October 10, 2026
Health & Medicine ResearchReported finding
Vitamin D2 Supplements May Lower the Body's D3 Levels, Study Finds
New research suggests vitamin D2 supplements may lower the body's vitamin D3 levels by 9 to 18 nanomoles per liter, challenging assumptions that the two forms are interchangeable.
By Elena Vasquez4 min read791 words
In brief
- A 2025 meta-analysis of 11 randomized controlled trials found vitamin D2 lowered 25-hydroxyvitamin D3 by 9 to 18 nanomoles per liter on average
- Researchers reviewed 20 studies in total, with 11 contributing to the main analysis published in Nutrition Reviews
- UK guidance advises considering 10 micrograms of vitamin D daily between October and March
- A 2026 review of 26 trials confirmed vitamin D2 still produces real biological effects, including lowering parathyroid hormone
- A separate Frontiers in Immunology study found vitamin D3, but not D2, stimulated type I interferon immune signaling
A 2025 meta-analysis of 11 randomized controlled trials found that people taking vitamin D2 supplements showed average reductions of 9 to 18 nanomoles per liter in their vitamin D3 levels, the form humans naturally produce from sunlight. The finding challenges the long-standing assumption that D2 and D3 are interchangeable.
The research, published in Nutrition Reviews, drew on a systematic review of 20 studies. Researchers from the University of Surrey, the John Innes Centre, and the Quadram Institute Bioscience led the work.
Why does the D2 versus D3 distinction matter?
Both forms can raise total vitamin D status. Vitamin D2, or ergocalciferol, comes from fungi or yeast exposed to ultraviolet light. Vitamin D3, or cholecalciferol, matches the form human skin makes after sun exposure. The U.S. National Institutes of Health notes that D3 tends to raise and sustain blood levels more effectively than D2.
In the UK, official guidance advises considering 10 micrograms (µg) of vitamin D daily between October and March, when sunlight is too weak for adequate skin production. D3 supplements have historically come from lanolin in sheep's wool, though lichen-based D3 now offers a vegan alternative.
What did the researchers find?
After taking D2, participants showed significantly lower concentrations of 25-hydroxyvitamin D3, the D3-derived compound doctors measure in standard blood tests, compared with non-supplemented groups.
Lead researcher Emily Brown, a PhD research fellow at the University of Surrey, said:
"Vitamin D supplements are important, especially between October and March, when our bodies cannot make vitamin D from sunlight in the UK. However, we discovered that vitamin D2 supplements can actually decrease levels of vitamin D3 in the body, which is a previously unknown effect of taking these supplements. This study suggests that subject to personal considerations, vitamin D3 supplements may be more beneficial for most individuals over vitamin D2."
The drop in D3 does not mean D2 is harmful. D2 still raises 25-hydroxyvitamin D2 and contributes to overall vitamin D status. The finding is that increasing one form can coincide with a decline in the other.
Why might D2 lower D3?
Scientists do not have a definitive answer. One hypothesis centers on the body's regulation of vitamin D. When vitamin D metabolites rise, the body may accelerate their breakdown to keep levels in check. Higher D2 intake could therefore increase disposal of existing D3.
Earlier experiments suggest the relationship runs in both directions, with D3 supplementation sometimes reducing D2-derived metabolites. How much this balancing effect influences health remains unresolved.
Could the immune system respond differently?
Separate work led by Professor Colin Smith of the University of Surrey, published in Frontiers in Immunology, examined how the two forms alter gene activity in blood. The team found substantial differences, including in immune-related pathways. Vitamin D3 appeared to stimulate type I interferon signaling, a key early-warning system against viruses and bacteria. D2 did not show the same effect.
Smith said:
"We have shown that vitamin D3, but not vitamin D2, appears to stimulate the type I interferon signaling system in the body — a key part of the immune system that provides a first line of defense against bacteria and viruses. Thus, a healthy vitamin D3 status may help prevent viruses and bacteria from gaining a foothold in the body."
These immune findings remain preliminary. Changes in gene activity do not necessarily translate into fewer infections, and larger clinical trials are needed.
What does newer evidence add?
A 2026 systematic review and meta-analysis examined 26 randomized trials of vitamin D2. It found D2 significantly reduced parathyroid hormone levels and produced a small increase in blood calcium, confirming D2 retains real biological effects even as it may lower D3.
Professor Cathie Martin of the John Innes Centre stressed the practical angle:
"This meta-analysis highlights the importance of ensuring plant-based vitamin D3 is accessible in the UK."
Professor Martin Warren, chief scientific officer at the Quadram Institute, framed the public-health stakes:
"Vitamin D deficiency represents a significant public health concern, especially during the winter months with significant deficiency across the UK population. Tackling this with the most effective form of vitamin D supplementation or fortification is of the utmost importance to the health of the nation."
What don't scientists know yet?
The main open question is whether the D3 reduction caused by D2 leads to meaningful differences in long-term health. Researchers call for more work on how the two forms are metabolized and whether their immune effects differ in everyday life.
For now, the evidence increasingly suggests that the label on a vitamin D supplement matters. D2 and D3 can both contribute to status, but D3 appears to hold an edge in raising and sustaining it.
via dx.doi.org (Original)
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