Outdoor athletes like cross-country runners who spend hours in the sun get enough vitamin D naturally. Indoor athletes or those in winter climates should supplement if they're not getting 15-20 minutes of direct sun three times a week.
Vitamin D comes from the sun, which is really cool. So if your athlete is a cross-country runner and they're in the sun multiple hours a week and they're getting sun exposure on their arms and their face, amazing. They probably don't need to supplement vitamin D. But if you are an inside athlete, if it is winter, if you're not getting at least 15 to 20 minutes of sun 3 times a week, you probably need to be supplementing with vitamin D.
