Researchers caution that a widely used vitamin D supplement could have an overlooked drawback.

This article discusses findings from recent research on vitamin D supplementation, particularly highlighting important differences between vitamin D2 and vitamin D3.

Key Points:

1. Vitamin D Forms:

   • Vitamin D2 (ergocalciferol) is typically derived from fungi/yeast.
   • Vitamin D3 (cholecalciferol) is produced in human skin from sunlight exposure and is also sourced from lanolin or lichen in supplements.

2. Research Findings:

   • A 2025 study found that taking vitamin D2 may reduce levels of vitamin D3 in the body, which is significant as D3 is more effective for raising and maintaining vitamin D levels.
   • The study reviewed 20 trials and determined that those taking D2 had lower levels of 25-hydroxyvitamin D3, with reductions of approximately 9 to 18 nanomoles per liter.

3. Health Implications:

   • Vitamin D is crucial for calcium absorption, bone health, and other bodily functions like muscle and immune response.
   • The U.S. National Institutes of Health recommend 10 micrograms of vitamin D daily, especially during the months with less sunlight.

4. Mechanism of Action:

   • It’s suggested that an increase in vitamin D2 may lead the body to increase the breakdown of vitamin D3 to maintain balance, although the exact mechanism is not yet fully understood.

5. Immune System Effects:

   • Research indicates D3 may positively affect immune responses more than D2. D3 appears to stimulate type I interferon signaling, which is important for early immune responses.

6. Current Guidance:

   • While both D2 and D3 can boost vitamin D levels, D3 is favored for more effective and longer-lasting elevation of those levels.
   • Newer studies continue to affirm D2’s role in reducing parathyroid hormone levels and slightly increasing blood calcium, indicating it has beneficial effects despite its impact on D3 levels.

Conclusion:

The evidence suggests that while both vitamin D2 and D3 are important, D3 may be more beneficial for overall vitamin D status and immune function. Future research is needed to understand the health implications of these findings fully and establish the best supplementation practices.