Vitamin D is a type of fat-soluble vitamin that is stored in your body. In its initial state, vitamin D is inactive, so it must go through a series of conversions in order to activate. Very few foods naturally provide vitamin D, so if you are deficient, you may need a supplement. If you decide to take a vitamin D supplement, talk with your physician first as a precautionary measure.
Function of Vitamin D
Vitamin D is most commonly known for its role in calcium absorption. It helps your body efficiently utilize and store calcium, and it keeps your bones and teeth strong. As cells grow and divide, vitamin D helps with cell differentiation, which determines which type of cell they will become. Vitamin D is necessary for insulin secretion. Insulin is a hormone that pulls glucose into cells for energy. Having inadequate vitamin D in your system can affect glucose tolerance if you have type 2 diabetes. Additionally, this powerful vitamin works by regulating your immune system and maintaining normal blood pressure levels.
Vitamin D Conversion
Vitamin D is often referred to as the "sunshine" vitamin since your body can synthesize it when skin is exposed to direct sunlight. In order for vitamin D from the sun, foods or supplements to become active, it must undergo two hydroxylations. The first one occurs in the liver where it is converted to 25-hydroxy vitamin D, or calcidiol, explains the Office of Dietary Supplements. For the second, a hydroxylation takes place in the kidney and forms 1,25-dihydroxy vitamin D, or calcitriol, the most potent form of vitamin D.
Types of Vitamin D
Vitamin D in foods and supplements is available as D2 or D3, which are both similar but have slightly different chemical structures. D2, known as ergocalciferol, and D3, called cholecalciferol, each undergo identical metabolism processes in your body. The biggest difference is that D2 is less potent at high doses. Small amounts of D3 are found in beef liver, cheese and egg yolks. Mushrooms are a natural source of D2.
Dosage
For you to reap all of the benefits of vitamin D, you need to consume 600 IU every day. Over the age of 70, you need as much as 800 IU to keep your bones strong. Vitamin D2 may not be efficient in fracture prevention, however, supplementation with D3 can help reduce bone loss and fractures in the elderly population, reports the Linus Pauling Institute. Most over-the-counter supplements are available in cholecalciferol, or D3.
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