About vitamin D...

D has been the star vitamin of the past few years, piling up study after favorable study even as the claims of its fellow vitamins are steadily
being debunked. According to various studies, vitamin D fights cancer, builds bones, combats heart disease, tunes up your immune system, and
provides a long list of other benefits. Since it’s produced in the body as a response to ultraviolet light from the sun, people who live far from the
equator are particularly at risk of deficiency in winter—which may explain why diseases like lung cancer and breast cancer are most likely to kill you
if you’re diagnosed during those gloomy months. You can get some vitamin D from sources like fatty fish and fortified milk, but the vast majority
comes from either sunlight or supplements.



In a study, researchers from the University of Manchester in Britain asked 99 adolescent schoolgirls to perform a series of one- and twolegged
jumps, then took blood tests to see how much vitamin D they had in their bodies. There was a clear correlation: the more vitamin D, the
higher, faster, and more powerful the jumps. To many, this was confirmation of what they’d suspected for some time: the “sunshine vitamin” could
turn out to be the ultimate natural performance enhancer. But it’s not quite that simple.

Interest in the sun’s potential as a performance booster dates back at least to a rudimentary Russian study in 1938 in which four students
improved their 100-meter dash time by 7.4 percent after a course of UV radiation, while controls improved by only 1.7 percent. In subsequent
decades, German researchers also tried boosting performance using sun lamps and identified vitamin D as the probable cause. But this research
petered out in the 1960s without any rigorous conclusions. Other studies have looked at vitamin D’s links with parameters like reaction time and
muscle protein synthesis. But, according to a review of the topic in Medicine & Science in Sports & Exercise, no studies have ever looked
for direct links between athletic performance and levels of vitamin D indicated by blood tests.
Much of the debate centers on how you define deficiency. According to a 2008 study in the American Journal of Clinical Nutrition, vitamin D
levels in American children and adults appear to have declined since the 1980s, possibly because people spend less time in the sun and drink less
milk. About half of adults now have sub-optimal levels of vitamin D, according to the study. Notably, three-quarters of the girls in the University of
Manchester study were found to be vitamin D deficient, which makes it less surprising that higher levels improved jumping performance. After all,
even a glass of water is performance-enhancing if you’re thirsty.



Several large-scale studies involving thousands of people are now in progress to untangle the cause-and-effect links between vitamin D and
various diseases. Despite the uncertainty, there’s enough evidence to suggest that you should be aware of your vitamin D levels and make sure
you either take supplements or get enough sun. Once you reach “normal” levels, there’s currently no evidence that further vitamin D will make you a
better athlete—but going from deficient to normal could definitely put a spring in your step.