Vitamin D is sometimes called the “sunshine vitamin” because it’s produced in your skin in response to sunlight. It’s a fat-soluble vitamin in a family of compounds that includes vitamins D-1, D-2, and D-3.

Your body produces vitamin D naturally when it’s directly exposed to sunlight. You can also get it through certain foods and supplements to ensure adequate levels of the vitamin in your blood.

Vitamin D has several important functions. Perhaps the most vital are regulating the absorption of calcium and phosphorus, and facilitating normal immune system function. Getting a sufficient amount of vitamin D is important for normal growth and development of bones and teeth, as well as improved resistance against certain diseases.