Clinical Controversies in Vitamin D: 25(OH)D Measurement, Target Concentration, and Supplementation

Despite a plethora of recent research and systematic reviews of available data, controversy continues to surround the definition of optimal vitamin D status, the daily intake needed, and the potential adverse health consequences of “insufficiency.” Efforts to standardize vitamin D measurement and improve understanding of the physiologic consequences of other vitamin D metabolites such as 3-epi and 24,25(OH)2D (and potentially other vitamin D compounds) are needed. Currently, measurement of circulating 25(OH)D is accepted as the approach to define an individual's vitamin D status. However, existing 25(OH)D assays may include other vitamin D metabolites such as the 3-epimer of 25(OH)D and 24,25(OH)2D. It seems unlikely that the controversy will soon be resolved.