One of the classic manifestations of vitamin D deficiency is reduced muscle strength, and if you want to be as strong as possible, you must avoid deficiency. Deficiency of course is relatively common, and supplementation is cheap and safe.
Professional ballerinas train indoors for up to 8 hours a day, with little exposure to sunlight. They tend to have low vitamin D levels in the wintertime. They are prone to injuries. At the Birmingham (UK) Royal Ballet, a study in 2012 demonstrated low vitamin D levels.
In this study, 24 volunteers were enrolled in a randomized trial. Seventeen received a 2,000 units of vitamin D a day for 4 months. Seven were controls.
The ballerinas taking the vitamin D had 19% higher quadriceps strength. They also could jump 3 cm higher, and had fewer injuries during the four months.
How does the increase in strength happen? It's not clear, but correcting vitamin D deficiency increases muscle protein synthesis, and increases muscle concentrations of ATP. (For non-healthcare-types, think of ATP as a bunch of little tiny batteries flying around in the body, giving energy where it is required.)
The ballerina study was not blinded, and not randomized, which makes it weaker. Nontheless the results are thought-provoking. How many injuries could be prevented with this simple intervention? How many athletic careers are cut short for lack of the few percentage points of performance vitamin D could provide?
And of course, in my fair city of Buffalo, how many Superbowls could have been won?