Efficacy of high-dose vitamin D supplements for elite athletes

Purpose: Supplementation with dietary forms of vitamin D is commonplace in clinical medicine, elite athletic cohorts and the general population, yet the response of all major vitamin D metabolites to high doses of vitamin D is poorly characterized. We aimed to identify the responses of all major vitamin D metabolites to moderate and high dose supplemental vitamin D3.

Methods: A repeated measures design was implemented in which 46 elite professional European athletes were block randomized based on their basal 25[OH]D concentration into two treatment groups. Athletes received either 35,000 or 70,000 IU.week-1 vitamin D3 for 12 weeks and 42 athletes completed the trial. Blood samples were collected over 18 weeks to monitor the response to supplementation and withdrawal from supplementation.

Results: Both doses led to significant increases in serum 25[OH]D and 1,25[OH]2D3. 70,000 IU.week-1 also resulted in a significant increase of the metabolite 24,25[OH]¬2D at weeks 6 and 12 that persisted following supplementation withdrawal at week 18, despite a marked decrease in 1,25[OH]2D3. Intact PTH was decreased in both groups by week 6 and remained suppressed throughout the trial.

Conclusions: High dose vitamin D3 supplementation (70,000 IU.week-1) may be detrimental for its intended purposes due to increased 24,25[OH]2D production. Rapid withdrawal from high dose supplementation may inhibit the bioactivity of 1,25[OH]2D3 as a consequence of sustained increases in 24,25[OH]2D that persist as 25[OH]D and 1,25[OH]2D concentrations decrease. These data imply that lower doses of vitamin D3 ingested frequently may be most appropriate and gradual withdrawal from supplementation as opposed to rapid withdrawal may be favorable.