Vitamin D

Vitamin D (also known as Calciferol) is a group of fat-soluble vitamins responsible for absorption of calcium and phosphate, and for the maintenance of adequate bloodstream levels of both, enabling normal mineralization of bone. Other uses are bone growth and remodeling, modulation of cell growth, neuromuscular and immune function, and reduction of inflammation. Its two major forms are D2 (ergocalciferol) and D3 (cholecalciferol).

Absorption
Vitamin D is obtained from diet intake and from endogenous production at the skin when exposed to ultraviolet radiation. A moderate exposure to sunlight usually lead to sufficient vitamin D synthesis, however carcinogen and skin ageing effects of ultraviolet radiation should be taken into consideration.

It is absorbed at the small intestine without problem. Vitamin D produced by the body is the D3 form. Vitamin D from the diet can be D2 or D3, depending of the source. Some controversy exists over whether or not D2 can fully substitute for vitamin D3 in the human diet.

Daily Dietary Recommendation
In sunlight-deprived individuals the endogenous production of vitamin D is insufficient and the Daily Dietary Recommendation should be raised to 1000 IU (25 μg).

Deficiency
Vitamin D deficiency causes rickets in children and osteomalacia in adults. Also leads to reduced absorption of calcium, which can result in osteoporosis in the long-term.

Hypervitaminosis D (Vitamin D Overdose)
The tolerable upper intake levels for Vitamin D is 4000 IU (100 μg) for those aged 9 and older, with corresponding lower amounts for younger.

Main effect of vitamin D overdose is hypercalcemia, and its main symptoms are those derived from it: anorexia, nausea, and vomiting among others. At doses of 50,000 IU (1250 μg) per day it can take several months for the symptoms to appear.