Vitamin D is important for maintaining bone health. It affects bones by controlling the body’s levels of calcium and phosphate, which are critical for building new bone. Vitamin D controls calcium and phosphate levels in three ways: by regulating how much we absorb from our diet, how much is within our bones, and how much we excrete.

We get vitamin D from our diet, sun exposure, and oral supplements like multivitamins. Only a few foods naturally contain vitamin D. These include some oil-rich fish, certain mushrooms, and egg yolks. Most of our dietary vitamin D comes from fortified dairy products, cereals, and bread products. The sun provides a major source of vitamin D, but sunscreen, which protects against sunburn and skin cancer, decreases the skin’s production of vitamin D.