Overview

• In a meta-analysis published in Nutrition Reviews, University of Surrey researchers report that vitamin D2 supplementation was linked to reduced levels of vitamin D3 in a majority of randomized trials.
• Several trials showed vitamin D3 concentrations fell below those seen in control groups not taking vitamin D, indicating a consistent D3-lowering effect during D2 use.
• Authors stress that D2 still raises overall measured vitamin D, yet prior evidence suggests D3 is more efficiently utilized and may be the preferable supplement for many people.
• The mechanism behind D2 lowering D3 remains unclear, with follow-up studies planned to assess bidirectional effects and with earlier research indicating D3-specific immune signaling activity.
• The findings arrive as winter supplementation is encouraged in higher latitudes, carrying particular relevance for vegans who often rely on D2 and face limited access to plant-based D3.