Vitamin D is most often referred to as a vitamin. However, it is really a steroid hormone obtained from sun exposure, food sources, and supplementation. Common forms of vitamin D are vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). Vitamin D3 is supposed to be 87 percent more effective than vitamin D2. Only a few foods contain vitamin D. Salmon, herring, tuna, mackerel, and fish oils are sources of vitamin D. Cooked egg yolk and beef liver also contain vitamin D. Milk is often fortified with vitamin D as are bread, juices, and other dairy products. Some multivitamins may contain vitamin D. Cooking foods variably reduces vitamin D content. Boiled, fried, and baked foods may contain 69 to 89 percent of the original vitamin D content. Animal sources of vitamin D are considered to be better than plant sources, which provide only vitamin D2.
Sun exposure may be the best source of vitamin D, as it provides UVB wavelengths that the body requires for vitamin D production. However, when the temperature is lower than 50 degrees F, there is a scarcity of UVB rays. The best time for exposure to the sun is as near to solar noon as possible. You will produce more vitamin D more rapidly at this time. It is recommended that you receive 20 minutes of direct sun on the skin of the arms for 4 to 5 times a week. During the winter months, the sun may be too low in the sky to produce vitamin D in the skin. It also may be hard to get adequate sun in cities with tall buildings.
Skin pigmentation affects the production of vitamin D. Fair skinned people can max out vitamin D production more rapidly than dark skinned people. The skin around the eyes is thinner than it is on other body parts. Skin protection is advised for this part of the body. Excessive use of sunscreen can decrease vitamin D production by the skin as it prevents much of the ultraviolet rays from reaching the skin.