January 4, 2008

2 min read

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More About Vitamin D

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Sources of Vitamin D
Vitamins D3 and D2 occur naturally in some foods, and both versions of the vitamin are added to certain “fortified” products. Foods provide relatively small doses of D compared with amounts made by the skin in response to UVB light. (IU = international units.)

  •  Cod-liver oil (1 tbsp): 1,360 IU D3

  •  Cooked tuna, sardines, mackerel or salmon (3–3.5 oz): 200–360 IU D3

  •  Shiitake mushrooms (fresh, 3.5 oz): 100 IU D2 (dried, 3.5 oz): 1,600 IU D2

  •  Egg yolk: 20 IU D3 or D2

  •  Fortified dairy products, orange juice or cereals (one serving): 60–100 IU D3 or D2

  •  Full-body exposure to UVB (15 to 20 minutes at midday in summer, fair skin): 10,000 IU D3

Tissues Affected by Vitamin D
The VDR receptor protein (above) is found in many body tissues as well as circulating immune cells, indicating a role for active vitamin D in regulating gene activity in those locations. The list below includes some of the tissues and cells where 1,25D action has been established.

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  •  Bone

  •  Brain

  •  Breast

  •  Fat

  •  Intestine

  •  Immune cells

  •  Kidneys

  •  Liver

  •  Nerves

  •  Pancreas

  •  Parathyroid gland

  •  Prostate

  •  Skin keratinocytes

D Makes a Difference
Growing evidence suggests that chronically low levels of vitamin D raise a person’s risk for certain major illnesses. Examples of findings based on a population’s blood serum D levels or UV exposure include:

  •  30% to 50% higher risk for breast, prostate and colon cancers at serum 25D levels below 20 ng/ml

  •  Five times higher risk of ovarian cancer among women living at high latitudes (for example, Norway and Iceland) than women living at equatorial regions

  •  77% lower risk for all cancers among Nebraska women age 55 and older taking 1,100 IU of D3 daily over a three-year period compared with a placebo group

  •  62% lower risk for multiple sclerosis at serum 25D levels above 40 ng/ml than at 25 ng/ml or less

  •  80% lower lifetime risk for autoimmune (type 1) diabetes in Finnish children given 2,000 IU of D3 daily during first year of life

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