Vitamin D Supplements May Not Be Necessary — and Can Interact With Medications[1] Your body needs vitamin D along with calcium to build bones and keep them healthy, and to support immune health, muscles, and brain cells. Some research has also found that vitamin D may prevent diseases like cancer and osteoporosis[2] Food sources of vitamin D include some types of fish, such as salmon, mackerel, and sardines; foods with added vitamin D, such as some cereals; juices; dairy products; mushrooms; and egg yolks. [1] Your body also makes vitamin D when your skin is exposed to direct sunlight. Ultimately, the biggest risk of taking vitamin D is likely wasting money on a supplement you don’t actually need. But it’s also important to also be aware of potential drug interactions and to speak with your doctor before you add vitamin D to your routine.