The body makes vitamin D when skin is directly exposed to the sun, and most people meet at least some of their vitamin D needs this way. Skin exposed to sunshine indoors through a window will not produce vitamin D. Cloudy days, shade, and having dark-colored skin also cut down on the amount of vitamin D the skin makes.
However, despite the importance of the sun to vitamin D synthesis, it is prudent to limit exposure of skin to sunlight in order to lower the risk for skin cancer.
Natural foods high in vitamin D include fish oils, fatty fish, mushrooms, beef liver, cheese, and egg yolks. In addition, vitamin D is widely added to many foods such as milk and orange juice.
Source:Healthaliciousness Article by Daisy Whitbread, a certified nutritionist, and Paul House, a health analyst