Fruits don't normally contain vitamin D, but some orange juice is fortified with the vitamin. Sunlight is the best source of vitamin D. Foods that are good sources of vitamin D include wild-caught fish, such as salmon and mackerel; canned fish, such as tuna and sardines; beef or calves' liver; egg yolks; and shiitake mushrooms. Many foods are fortified with vitamin D, including milk and other dairy products, cereals, oatmeal, orange juice and tofu.
When the sun's ultraviolet rays strike the skin, it triggers the body to synthesize vitamin D. Twenty to 25 minutes of sun exposure per day normally provide a person with sufficient levels of vitamin D, but many people find it difficult to obtain sufficient vitamin D this way. Those living in latitudes farther from the equator are unlikely to obtain enough vitamin D from sunlight during the winter months because the sun's rays are not strong enough at that time of year. In addition, conscientious use of sunscreen blocks the skin's absorption of vitamin D year round, and as skin ages, it is more difficult for it to absorb vitamin D.
The recommended daily allowance of vitamin D for most people is 600 international units. Three ounces of salmon contains 425 international units, 3 ounces of mackerel contain 547 international units and an egg yolk contains 41 international units. Since too much vitamin D can be toxic, individuals age 9 and above should strive to obtain no more than 4,000 international units each day.
Vitamin D helps strengthen bones, regulate blood pressure and the immune system and prevent the development of Type 2 diabetes, depression and some kinds of cancer. It may also help prevent premature death.