The D vitamin is the only vitamin that is not obtained from foods that you eat. Rather, the natural source of Vitamin D is obtained by sunlight on the skin.
Most people these days are well aware of the dangers of too much exposure to the sun but fortunately the amount of time you have to spend in the sun to receive a sufficient dose of the D vitamin is extremely small and just a few minutes a day is sufficient. This small amount should not have any adverse effects from the amount of ultra-violet light received.
The most important function of the D vitamin is to help control how much calcium is absorbed from food. The majority of the calcium is used to build strong teeth and bones but calcium is also needed to transmit electrical impulses along our nerves and to help muscles, such as the heart muscles, to contract.
Vitamin D is critical in ensuring that there is always sufficient calcium in the blood to perform these tasks. Other functions that require the D vitamin are concerned with your immune system and it is believed that it is also a contributing factor in reducing the risk of contracting cancer particularly colon cancer.
The D vitamin is created when the ultraviolet in the sunlight reacts with a type of cholesterol that is found under the skin naturally. This is converted into a more active form of the D vitamin in the liver. Some of the vitamin D remains in the liver and kidneys to help reabsorb the calcium from the blood. The remainder of the D vitamin is dispersed to the bones to help them retain their calcium and the intestines to aid absorption of calcium from food.