New research suggests that vitamin D2 supplements may lower the body's levels of vitamin D3, the form naturally produced by sunlight. The meta-analysis, published in Nutrition Reviews, reviewed 20 studies and found that people taking vitamin D2 had significantly lower concentrations of 25-hydroxyvitamin D3 — the form doctors measure to assess vitamin D status — by roughly 9 to 18 nanomoles per liter compared with those who did not take D2.
The two forms are often treated as interchangeable, but the findings add to evidence that D3 is more effective at raising and maintaining overall vitamin D levels. The U.S. National Institutes of Health notes that D3 tends to raise levels more and keep them elevated longer than D2. The exact mechanism is unclear, but researchers suggest that rising vitamin D metabolite levels may accelerate the body's breakdown of D3. Earlier studies also indicate D3 may stimulate type I interferon signaling, which is involved in immune response, while D2 did not show the same effect.
The study's lead researcher said that, subject to personal considerations, D3 supplements may be more beneficial for most people. Plant-based D3 derived from lichen is now available, which may matter for those avoiding animal products. However, the clinical significance of the D2-D3 balancing effect remains unresolved, and the researchers note that D2 itself still raises overall vitamin D status. The UK advises 10 micrograms of vitamin D daily during darker months when sunlight is insufficient. — that's 3 paragraphs. Good. Need to ensure not copying source wording. I'll rephrase. Also note the source says