Vitamin D levels
Sunlight helps the body make vitamin D—an important nutrient for healthy bones, brains, and more. Vitamin D is found naturally in very few food sources, so people need to get it either from sun exposure, supplements, or fortified foods, like milk. (Fatty fish, such as salmon, naturally contain vitamin D.)
You don’t need much sunlight to get adequate vitamin D, especially if you have pale skin or red hair; for most people, just 5 to 30 minutes twice a week, with your face, arms, legs, or back exposed without sunscreen is enough. But still, many Americans don’t get enough. And because of very real skin-cancer concerns, the American Academy of Dermatology recommends getting your vitamin D from a healthy diet and/or supplements—not from the unprotected sun exposure.