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.

  •  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