Vitamin D, also known as “the sunshine vitamin,” helps the body absorb calcium. It is therefore needed for strong bones. It also helps perform other important bodily functions, such as stimulating your pancreas to make insulin and regulating your immune system. The greatest source of vitamin D comes from sun exposure, which many people don’t get enough of during winter months or when living in big cities. In these cases, it is important to consume foods, such as fish, some varieties of mushrooms, egg yolks and fortified milk that provide this essential vitamin.