Vitamin D is the only vitamin synthesized in your skin. It is important to note, however, that the skin can only synthesize vitamin D with the help of ultraviolet rays from the sun. Vitamin D belongs to the group of vitamins referred to as fat-soluble vitamins. Fat-soluble vitamins require the presence of dietary fat in order to be properly absorbed by the body.
Physiology
Your skin contains a cholesterol compound that is converted to a structure called previtamin D when exposed to sunlight. When this structure reaches your bloodstream, it is converted to an inactive form of vitamin D that travels to the liver. The inactive form of vitamin D gets filtered through the liver and then re-enters your bloodstream. The inactive form of vitamin D circulates throughout your bloodstream until it reaches the kidneys, where it is converted to an active form.
Considerations
Although the ultraviolet rays from sunlight are essential to synthesizing vitamin D in your skin, the Office of Dietary Supplements notes that you should limit your sun exposure. If you plan on being out in the sun for an extended period of time, you should wear protective clothing and a sunscreen that contains SPF, which can lower your risk of skin cancer.
Functions of Vitamin D
The primary function of vitamin D is its role in bone health. When vitamin D is converted to its active form, it helps regulate the minerals calcium and phosphorus. Vitamin D increases the absorption of these minerals and ensures that the levels of these minerals remain high enough to keep your bones strong. Vitamin D also helps to regulate the growth of certain cells that can cause cancer. The Linus Pauling Institute notes that while high levels of vitamin D have been associated with lower cancer risk, it has not been proven that vitamin D can prevent the development of cancer. Similarly, the Institute indicates that vitamin D has been linked to lower incidences of diabetes, although whether vitamin D can prevent the development of the chronic disease remains to be proven.
Daily Recommendations
Sun exposure differs in certain geographical areas, so it can be difficult to determine exactly how much vitamin D is produced in your skin. Because of this, the Food and Nutrition Board provides recommendations for how much vitamin D you should consume in your diet. Adults should aim to consume between 5 to 15 micrograms, or mcg, of vitamin D daily.
Very few foods contain significant amounts of vitamin D, so it is often difficult to meet daily vitamin D needs, according to "Nutrition and You" by Joan Salge Blake. The best sources of dietary vitamin D include fortified milk, fortified cereals, yogurt and fatty fish, such as salmon.
References
- "Nutrition and You": Joan Salge Blake; 2008
- Office of Dietary Supplements: Vitamin D
- Medline Plus: Vitamin D
- Linus Pauling Institute: Vitamin D
