The only vitamin that is not obtained by food is vitamin D, instead it is obtained by sun light.The amount of time you need to have your skin in exposure to sun light, to receive the recommended daily dose is actually just a few minutes so there isn't any big risk of vitamin D deficiency.
Vitamin D`s functions relate to the immune system and the control of the amount of calcium absorbed from the food.
The most important function of the vitamin D 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 it is also needed to send messages along the nerves and to help muscles, such as the heart muscles, to contract. It is the vitamin D that ensures that there is always sufficient calcium in the blood to perform these tasks.
Immune system relatedVitamin D deficiency is related with cardiovascular disease, multiple sclerosis, rheumatoid arthritis, and type 1 diabetes mellitus. It is also believed that that vitamin D is also a contributing factor in reducing the risk of contracting cancer and, in particular, colon cancer.
Vitamin D3 or cholecalciferol
The variant of the vitamin D that is formed under the skin is known as vitamin D3, or cholecalciferol. This vitamin D is created when the ultraviolet in the sunlight reacts with a type of cholesterol that is found under the skin naturally. The D3 is converted into a more active form of the d vitamin in the liver and is then diverted to where it is needed the most. Some of the vitamin D remains in the liver and kidneys to help reabsorb the calcium from the blood. The rest of the vitamin D is dispersed to the bones to help them retain their calcium and the intestines to aid absorption of calcium from food.
Vitamin D2 or ergocalciferol
I said that the vitamin D is formed from the sunlight exposure of the skin and not obtained by food , but there is one form that you can find in food and it is vitamin d2 or ergocalciferol. It is found in milk, yogurt, margarine, oil spreads, breakfast cereal, pastries and bread. This is used in the same way as the other D vitamins and is the type used to create the majority of D vitamin supplements.
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