Cholecalciferol

Cholecalciferol (inactive form)

Cholecalciferol (also known as vitamin D₃) is the kind produced by the body. It is a type of vitamin D. It is also found naturally in marine oils and in lanolin (oil from sheep's wool), the most common source for supplements.

Dietary sources

Few foods naturally contain much D₃. Fish do, especially oily ones, such as salmon, sardine and mackerel.

Production in body

D₃ is made in the skin from cholesterol, and changed into a more active form by the liver. However, the skin will not make it unless enough ultraviolet light shines on it. As sunlight contains ultraviolet light, getting enough sun is one way of getting enough D₃. The sun (UV rays) helps the body make an inactive form of vitamin D₃ from cholesterol. When there is less sunlight, less D₃ is made in the body. The inactive vitamin D₃ is processed by the liver into its active (useful) form.

Vitamin D synthesis by the liver from cholesterol into its active form calcitriol (25-hydroxyvitamin):

7-Dehydrocholesterol by sun (UV) rays → cholecalciferol in liver → calcidiol

The processed vitamin D is now 25-hydroxyvitamin D₃ a (called calcitriol).

Deficiency

Many things can keep the skin from making enough D₃. Winter sunlight may be too weak. Melanin, which protects skin from damage, also keeps it from making D₃, which is why people with darker skin are more prone to deficiency. Older people are also prone, because aging skin makes less D₃, even with enough sunlight. Clothing, glass, sunscreens and sunblocks also shield the skin from getting enough ultraviolet light to make D₃. Sun cream can block some UV radiation, but it does this on purpose to prevent sunburn and cancer.

Related pages

• Ergocalciferol