Dhaka:Recent research has indicated that vitamin D2 supplements may unexpectedly lower levels of vitamin D3, which is naturally produced in the skin upon sunlight exposure. While both forms of vitamin D are often thought to be interchangeable, evidence shows that vitamin D3 is generally more effective at increasing and maintaining vitamin D levels in the blood.
According to United News of Bangladesh, The U.S. National Institutes of Health highlights that vitamin D3 tends to elevate and sustain vitamin D levels more effectively than vitamin D2. Vitamin D plays a crucial role in calcium absorption and maintaining healthy bones, as well as supporting muscle, nerve, and immune functions.
A study published in Nutrition Reviews in 2025 reviewed 20 studies, out of which 11 contributed data for a primary analysis. It was found that individuals taking vitamin D2 had significantly lower levels of 25-hydroxyvitamin D3, a key marker for assessing vitamin D status in blood tests. The average reduction ranged from 9 to 18 nanomoles per liter, contingent on the analysis method.
Despite the findings, researchers clarified that vitamin D2 is not necessarily harmful, as it increases another form of vitamin D, contributing to overall vitamin D levels. Emily Brown, the lead researcher from the University of Surrey, suggested that vitamin D3 might be more advantageous for most individuals, depending on specific circumstances.
The exact reason why D2 reduces D3 levels remains unknown, with one hypothesis suggesting that increasing one form may prompt the body to break down existing compounds more rapidly. Previous studies have also shown that D2 and D3 might differently impact the immune system, with D3 enhancing activity related to type I interferon signaling, aiding infection response. However, this does not conclusively prove that D3 prevents infections.
A separate 2026 review of 26 randomized trials revealed that vitamin D2 still exerts significant biological effects, such as reducing parathyroid hormone levels and slightly elevating blood calcium. Researchers emphasize the need for further studies to ascertain whether the distinctions between D2 and D3 lead to significant long-term health effects. Presently, evidence increasingly suggests that D2 and D3 are not completely interchangeable, with D3 showing greater efficacy in raising and sustaining vitamin D levels.