High-dose vitamin D: helpful or harmful?

Abstract

If the optimal serum 25(OH)D level for skeletal health is 30 ng/mL or greater, then vitamin D insufficiency is widespread, affecting about 75% of adults based on a recent survey of more than 20,000 Americans. However, after a comprehensive analysis of existing research studies, the Institute of Medicine recently concluded that nearly all individuals are vitamin D replete when their 25(OH)D levels are 20 ng/mL or greater. Furthermore, two recent publications challenge the belief that 25(OH)D levels greater than 30 ng/mL are optimal for bone health. In a randomized, placebo-controlled trial, high-dose, once-yearly vitamin D therapy increased the incidence of fractures and falls. The second study reported that high-dose vitamin D did not reduce levels of parathyroid hormone or bone resorption among adults with 25(OH)D levels less than 32 ng/mL at baseline. It is time to question whether serum 25(OH)D levels of 30 ng/mL or greater are necessary for all individuals.

Figure 1

Relationship Between Achieved 25(OH)D Level and Relative Risk of Hip Fracture [30] Data from the study in which subjects achieved a serum 25(OH)D level of 105 nmol/L (42 ng/mL) reflects measurement of levels in a subset of 52 of 3270 subjects randomized to placebo or tricalcium phosphate and vitamin D [31]. The authors used a competitive binding assay to measure serum 25(OH)D levels. The assay works by displacing [³H]25(OH)D₃ from the plasma vitamin D binding protein, and thus the assay can overestimate serum 25(OH)D levels due to interference from other substances that are co-extracted when preparing the sample for analysis [1].