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Information on the latest vitamin D news and research.

Find out more information on deficiency, supplementation, sun exposure, and how vitamin D relates to your health.

Conflicting reports on vitamin D and athletic performance

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

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.

3 Responses to Conflicting reports on vitamin D and athletic performance

  1. IAW says:

    So to state the obvious the biggest difference I see is in the original study they gave daily dosing of Vitamin D and this new study they gave the Vitamin D in big doses “once a week”. I then find the statement “although at 12 weeks, there was no significant difference between the two groups” fascinating.(Referring to blood levels even though one group was given higher amounts.)

    So, like Dr. Cannell, I believe daily dosing is best. What does your body do when given a high amount of Vitamin D with probably only so much in co-factors to go with it at the time?

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  2. ANY study that does not address the “mother nature” blood level as the key assessment criteria for any legitimate evaluation of effect is fundamentally flawed.
    If the human model is designed to acquire a certain amount of cholecalciferol DAILY then what possible justification can there be for the aberrant notion of weekly massive dosing? The half-life of the molecule is not the issue. It is what is “normal” in how we are adapted in evolution to acquire a blood level of 25(OH)D approximating ~50 ng/ml (and for athletes who likely both acquire more cholecalciferol when exercising outdoors AND metabolize more when exercising, ~60-65 ng/ml).
    Consider the prior study performed and the methodology as well as the conclusions, in constrast to this second study wherein there is a stated failure to reach the MN blood level. (MN=Mother Nature)
    Studies MUST be designed with the normal human-in-nature blood level as the fundamental controlling factor, NOT some WAG dosage the author arbitrarily chooses out of ignorance.

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  3. TheFarSide says:

    I suspect that many studies that produce an ambiguous finding, as this one does, do so because Vitamin D’s co-factors are not given to subjects. I have yet to read a study that states co-factors were given to subjects. Presumably this is because the study designers assumed co-factors are unneeded or were unaware of the importance of co-factors. My own experiments with Vit. D indicates that an adequate supply of co-factors is vital.

    Despite a commitment to supplementing with Vit. D at a fairly high dose (5kIU/d) I remain skeptical that pills are a effective replacement for sunlight. Sun exposure makes me feel good in a way that pills never do. This observation makes me somewhat skeptical of the validity of all Vit. D research that involves feeding pills to subjects.

    Intermittent dosing (e.g. weekly) may not be a bad as it appears on the surface. Throughout much of the world the sun does not shine every day in a predictable way. So it seems fair to suspect that throughout man’s evolution we adapted to a intermittent dosing scheme.

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