The body's natural production of vitamin D in the skin, which is accomplished with the help of radiation from the sun, is the primary connection between vitamin D and sunlight. The production of vitamin D is one of the primary functions of the skin, along with more obvious features like feeling and insulation. When the skin is struck by ultraviolet light from the sun, it produces a substance that the body can convert into vitamin D. In areas with strong enough sunlight, regular exposure to the sun's rays can produce enough vitamin D to meet the body's requirements. Due to the connection between vitamin D and sunlight, this vitamin is often informally called the sunshine vitamin.
The synthesis of vitamin D in the skin begins when a modified type of cholesterol naturally present in skin cells is exposed to sunlight. Specifically, the molecule is exposed to an invisible type of light, known as ultraviolet B (UVB), which converts it into a substance called cholecalciferol. Cholecalciferol is then transmitted through the bloodstream to the liver and kidneys, where it is further modified to become the active form of vitamin D, also known as calcitriol. The relationship between vitamin D and sunlight helps the body carry out a number of important functions. The most important of these is the maintenance of healthy bones and teeth.
Differing geographical locations can affect the relationship between vitamin D and sunlight. In northern latitudes, weaker and less frequent sunshine reduces the skin's opportunities to manufacture the vitamin D precursor. Also, since such climates tend to be colder, people are more likely to wear heavy clothing and spend more time indoors, further decreasing time spent in the sun.
Pollution and cloud cover can also reduce the amount of ultraviolet light that reaches the earth's surface. Still, five to 15 minutes of daily, unprotected exposure to sunlight is probably enough to meet most peoples' need for vitamin D. Longer periods of exposure to the sun's rays increases the risk of skin cancer. It also makes the skin age more quickly, which increases the occurrence of wrinkles and spots.
While environmental factors can disrupt the relationship between vitamin D and sunlight, this vitamin can also be obtained through food or supplement sources, where it is absorbed in the intestine. Good food sources of vitamin D include cold-water fish, egg yolks, and fortified foods like milk or breakfast cereals. Vitamin D can also be purchased as a supplement and is usually included in multivitamin formulas.