A very good friend of mine’s daughter is planning to write a dissertation for a school project. She previously had a stress fracture and then turned out to have very low levels of vitamin D. When I offered advice regarding testing and taking of vitamin D, I mentioned that the vitamin D might have some side-benefits for her. She is a keen and talented athlete. As I mentioned to her father, there’s quite a lot of evidence linking vitamin D with enhanced fitness and sporting performance. Her father suggested that a good subject for his daughter’s dissertation might be vitamin D in athletes, and I am very inclined to agree.
This reminder of the role of vitamin D physical function caused me to search for a relevant review study I had lurking on my hard drive . Sporting and physical performance has some seasonal variation: peaking in late summer before dropping off again in the autumn (fall) and winter. The idea here is the higher levels of vitamin D from sunlight exposure improves athletic performance. Some direct evidence comes for this idea in the form of evidence finding that vitamin D can enhance muscle synthesis and strength, as well as balance and reaction time.
The main point of this post, is to briefly summarise the evidence the review presents in terms of the impact of light on fitness and physical performance. Here’s a summary of the findings of the main studies highlighted by the review and their dates:
1938 – ultraviolet irradiation found to improve speed in the 100-metre sprint in four students compared with matched controls. Average times improved 1.7% in the non-irradiated controls undergoing training compared to 7.4% in irradiated students undergoing identical training.
1944 – 32 medical students were exposed to UV light, twice a week for 6 weeks. This led to a 13 per cent improved performance on a stationary bike compared to no improvement in controls.
1945 – irradiation over a 10-week period in individuals undergoing training saw a 19 per cent increase in fitness, compared to a 1.5 per cent improvement in controls.
1952 – German schoolchildren were exposed to UV lights at school for 9 months of the year. Compared to non-exposed children, light-exposed children were 56 per cent fitter in the early spring. This study also found that supplementing children with vitamin D replicated the effects of light exposure in terms of fitness enhancement.
1954 – UV light in the vitamin D-producing range was found to be most effective for increasing performance on a stationary bike.
1956 – UV light found to improve muscle strength and cycling performance in 6 out of 7 subjects.
1967-69 – Three studies that found a single dose of UV light found to improve strength, speed and endurance in women.
This research, spanning several decades, presents a quite powerful argument for optimisation of vitamin D levels in athletes and other looking to get the best from their bodies, I think. It seems odd that one little vitamin might have the power to enhance physical functioning in this way. Except that vitamin D is not a vitamin, it’s a hormone – and one that is being recognised as having wide-ranging benefits for the body.
The review that forms the basis for this post also quotes evidence finding that in populations, physical functioning is best at a vitamin D level of about 50 ng/ml (125 nmol/l). Such levels are also linked with protection from a wide variety of ills including heart disease and several forms of cancer.
1. Cannell JJ, et al. Athletic Performance and Vitamin D. Med Sci Sports Exerc 2009;41(5):1102-10