Vitamin D is a general term used to describe several forms of a compound with vital importance for the proper absorption of calcium in bone, as well as the maintenance of blood levels of calcium and phosphorus. When certain forms of light fall on your skin, they trigger the production of a form of the vitamin called cholecalciferol, or vitamin D3.
Vitamin D Production
The production of vitamin D in your skin begins with exposure to any light in the ultraviolet B wavelength, according to the National Institutes of Health’s Office of Dietary Supplements. Once this light penetrates your skin, it alters the composition of a skin compound called cutaneous 7-dehydrocholesterol. This alteration results in the creation of vitamin D3. Since vitamin D can be derived in this manner as well as from outside sources, scientists do not consider it a true vitamin, Colorado State University reports.
Vitamin D Conversion
Your body cannot directly use the vitamin D3 generated in your skin, according to Colorado State University. Before it becomes biologically active, it must first travel to your liver, where it is converted into a substance called 25-hydroxycholecalciferol. This new substance then passes on to your kidneys, where it is converted a second time into a form of usable vitamin D called 1,25-hydroxycholecalciferol. These intermediate and final forms of vitamin D flow through your bloodstream with the help of a specialized carrier protein called vitamin D-binding protein. Vitamin D from food sources follows a similar conversion pathway.
Sun Exposure Factors
You can gain enough vitamin D to fulfill your body’s needs by exposing your skin to sunlight three times each week in sessions lasting 10 to 15 minutes, according to the U.S. National Library of Medicine’s Medline Plus. However, certain factors can interfere with sufficient sun exposure. The Office of Dietary Supplements lists examples of these factors that include time of day, season of the year, geographical latitude, smog levels, cloud cover, use of sunscreen and the melanin content of your skin. Ultraviolet B radiation cannot pass through glass, so you may gain inadequate amounts of vitamin D if you sun yourself with light that falls through a window.
Vitamin D needs must be balanced with the known dangers of exposure to sunlight and the ultraviolet radiation generated in tanning beds, the Office of Dietary Supplements notes. Each year, roughly 1.5 million Americans develop skin cancer, and sun exposure is responsible for a majority of these cases. In addition, habitual sun exposure can produce significant cosmetic skin changes and contribute to the development of chronic skin dryness. Scientists do not know if you can gain adequate amounts of skin-generated vitamin D without increasing your long-term cancer risks.
As an alternative to sun exposure, you can gain your regular intake of vitamin D from fortified foods and supplements that contain vitamin D, according to the Office of Dietary Supplements. Nonhuman sources of vitamin D3 include chemically converted cholesterol and irradiation of lanolin, a fatty substance derived from the sebaceous glands of wool-bearing animals, such as sheep. Supplements containing vitamin D3 may provide greater benefits than other forms of the vitamin.