Formation and Function of Vitamin D in Our Body - NutriExpert
Guide to Vitamin D
Vitamin D is the only vitamin that is not obtained from the food we eat. Instead, vitamin D is actually obtained from sunlight on the skin. Much has been made in the media about the dangers of too much sun, but it is essential that the skin be exposed to sunlight to get the recommended daily allowance of vitamin D. In reality, the amount of time a person needs to spend in the sun to get a sufficient dose of vitamin D is extremely low. A few minutes a day is all that is needed and the amount of ultraviolet light received has no adverse effects.
The most important function of vitamin D is to help control the amount of calcium absorbed from food. Most calcium is used to build strong teeth and bones, but it is also needed to send messages along the nerves and to help muscles, such as the heart muscles, contract. It is vitamin D that ensures there is always enough calcium in the blood to do these things. Other functions that require vitamin D involve the immune system and it is also thought to help reduce the risk of getting cancer and, in particular, colon cancer.
The variant of vitamin D that forms under the skin is known as vitamin D3, or cholecalciferol. This vitamin D is created when ultraviolet light from the sun reacts with a type of cholesterol that is naturally found under the skin. D3 is converted to a more active form of vitamin D in the liver and is then directed to where it is needed most. Some of the vitamin D remains in the liver and kidneys to help reabsorb calcium from the blood. The rest of the vitamin D is dispersed into the bones to help them retain their calcium and into the intestines to help absorb calcium from food.
Although the majority of vitamin D is formed by exposure of the skin to sunlight, some foods naturally contain some of this vitamin. This form of vitamin D is known as vitamin D2, or ergocalciferol. It is used in the same way as other vitamin D and is the type used to create the majority of vitamin D supplements.
