Vitamin D and sports
From Scotland’s Health Deficit    2008

pg 36 UV radiation knocked seconds off 100m dash
In 1952 Spellerberg, a sports medicine researcher in Germany, reported further experiments showing improvements in athletic performance after irradiation with a UV lamp. The results were sufficiently impressive for the Sports College of Cologne to officially notify the “national German and international Olympic committee”. 
Meanwhile behind the Iron Curtain, in the heyday of the communist empire, athletes, trainers and their medical advisers were under great pressure to produce sporting results that reflected the greatness of Marxism– Leninism. In 1938 Russian sports scientists showed that college students who underwent a course of UV irradiation as part of training were able to knock a second off their average time in the 100m dash [376]. Students not given the irradiation improved by only two-tenths of a second. And so the Russians pushed their athletes hard, encouraged them to top up their vitamin D, and won many medals in the 1960s and 70s. 
A number of other researchers have reported benefits from using sunlamps and boosting vitamin D including: improved athletic performance, improved cardiovascular fitness, better muscular endurance, improved muscle strength, reduction in resting pulse and improved reaction times [374]. Other experiments have shown that taking vitamin D supplements can actually increase muscle mass and increase the number of “fast twitch” fibres that are crucial to athletic performance, at least in people who are not getting enough vitamin D in the first place [374].
A recent review entitled Should we be concerned about the vitamin D status of athletes? concluded: “. . . it is  likely that compromised vitamin D status can affect an athlete’s overall health and ability to train (i.e. by affecting bone health, innate immunity, and exercise-related immunity and inflammation). Although further research in this area is needed, it is important that sports nutritionists assess vitamin D (as well as calcium) intake and make appropriate recommendations that will help athletes achieve vitamin D status: serum 25(OH)D of at least 75 or 80 nmol/L.” This review provides much useful detail for those advising athletes on their health [377].
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3. Risks and benefits of sun exposure: 2,000:1 in favour of exposure