Differences in the absorption and metabolism of vitamin D₂, vitamin D₃, and 25 hydroxyvitamin D

A challenge for public health is to make recommendations for the intake of vitamin D to optimize health and prevent disease. Vitamin D supplementation can be accomplished using vitamin D₂ (from fungi), vitamin D₃ (from vertebrate sources), or as the prehormone 25 hydroxyvitamin D₃ (25OHD₃). While these three sources are generally effective for raising and maintaining vitamin D status, their effect is not identical. This review will summarize the differences between these molecules in their routes of absorption, their metabolism, degradation, and molecular function.