· Vitamin D is the fat-soluble vitamin that functions to maintain the calcium balance of your body. 
· Vitamin D stimulates dietary calcium absorption in the intestine and calcium deposition in bones.
· Vitamin D deficiency causes the disease Rickets which is a bone disorder.
· Vitamin D functions as a hormone more than vitamin.

· Vitamin D comes in different forms:
vitamin D2 (called ergocalciferol) is the dietary form of vitamin D found in plants, multiple vitamins and milk.
vitamin D3 (called cholecalciferol) is the form made from the exposure of skin to sunlight.

· Vitamin D recommended daily requirements:
There is no consensus regarding Vitamin D daily requirements.
The recommended dietary allowance of vitamin D for infants and children is 400 IU but this dose was based on a previously common dose equivalent of a teaspoon (5 ml) of cod liver oil.
This has traditionally been considered safe and effective in preventing Rickets.
Adults require less vitamin D than infants and children so the adult dose was set arbitrarily at 200 IU.
The optimal dose of vitamin D is not known.

· Recent studies have shown lower levels of vitamin D is becoming more common and that there has been an increase in cases of of vitamin D-dependent Rickets.
· Lower vitamin D levels are likely related to the use of sunscreen and sunlight avoidance.

· Vitamin D receptors are found in cells throughout the body and vitamin D likely has many more functions other than just regulating calcium levels.
· Vitamin D deficiencies and complications associated with low vitamin D levels are only recently being appreciated by the medical community.