There is an increasing body of evidence suggesting that sufficient vitamin D levels play a role in athletic performance. Dr Graeme Close and colleagues in Liverpool are especially interested, publishing numerous studies on the topic.
His latest study reports that supplementing athletes with high-dose vitamin D elevates vitamin D concentration, but doesn’t improve measures of physical performance. This study offers conflicting results compared with his previous research on the subject.
Dr Close and colleagues randomized 25 healthy athletes to take either 20,000 IU vitamin D, 40,000 IU vitamin D, or placebo once a week for 12 weeks. The athletes completed physical performance tests at baseline, 6 weeks, and 12 weeks and additionally had vitamin D status assessed.
At baseline, 57% of athletes were vitamin D deficient with vitamin D levels < 20 ng/ml, with 20% classified as severely deficient. The researchers report a significant difference between vitamin D levels over 12 weeks in all groups. Six week supplementation with 40,000 IU induced greater increases in vitamin D status than 20,000 IU, although at 12 weeks, there was no significant difference between the two groups. The placebo group’s vitamin D status decreased notably over the course of the study. There were no significant athletic performance changes during the 12 week study.
The researchers hypothesize that the particular vitamin D concentrations achieved by the athletes may not be optimal for muscle function. “…the optimal 25[OH]D concentration for a perceptible physiological response in one tissue may not be optimal for another. A higher serum total 25[OH]D concentration may be necessary in skeletal muscle…whereas in another tissue, a lower concentration is sufficient for a response,” Dr Close explains.
The group’s previous research included 30 athletes, and 30 age-matched non-athletes randomized to take either 5,000 IU vitamin D or placebo daily. The vitamin D group demonstrated significant increases in various athletic performance assessments. They did not discuss this research in the latest publication.
The authors call for research with larger sample sizes, longer supplementation protocols, and a greater dosage of supplementation.
Close GL, Jeckey J, Patterson M, Bradley W, Owens DJ, Fraser WD, Morton JP. The effects of vitamin D3 supplementation on serum total 25[OH]D concentration and physical performance: a randomized dose-response study. British Journal of Sports Medicine. Jan 2013.