Sources

• D-3 is available in limited amounts from dietary sources such as fish, egg yolks and cheese. It is also produced in an inactive form by the skin when exposed to sunlight.
  
  

Functions

• D-3 is used by the body for regulation of calcium, phosphate and magnesium absorption. It also plays a role in cell differentiation, immunity and insulin secretion.
  
  

Deficiency

• D-3 deficiency can cause childhood bone deformities and osteomalacia, which produces muscular and bone pain. Lack of sunlight exposure, kidney or liver dysfunctions, or genetic defects related to D vitamin receptors can all lead to deficiency.
  
  

Toxicity

• D-3 toxicity is typically the result of excessive D vitamin supplementation. It can result in nausea, weakness, constipation, and high blood calcium levels--which can alter heart function and psychological state.
  
  

Dosage

• The safe upper limit that has been established for daily intake of Vitamin D is 2000 Internation Units (IU) or 50 micrograms per day. Approximately 400 IU is the standard fortification in a glass of milk.