Vitamin D is produced photochemically in the skin

Vitamin D is a fat soluble vitamin and is present naturally in very few foods and is available as food additive and food supplement. However it is synthesized by human body when exposed to direct sun light.

Vitamin D helps in the absorption of calcium in the intestines and also its re-absorption in the kidneys. It helps in attaining and maintaining the serum levels of calcium and phosphates in the blood. This helps in the mineralization of the bones. Vitamin D promotes bone growth, bone remodeling and with out sufficient vitamin D bones may become brittle, thin and misshapen. Together with calcium it protects the elderly people from osteoporosis.

In the human body vitamin D has other roles like reduction of inflammation, neuromuscular activities and immune functions. vitamin D is believed to reduce the risk of colorectal, breast and prostate cancers.

Deficiency
Vitamin D deficiency may arise from inadequate consumption of its source foods, insufficient exposure to sun light and from disorders limiting its absorption in gut and its re-absorption from kidneys.

The deficiency lead to Rickets in children and softening of bones and osteoporosis in adults. Rarely deficiency may be hereditary. Rickets in children may result in stunted growth and misshapen long bones resulting in deformity.

Osteomalacia occurs in elderly people with symptoms of muscle weakness and fragile bones due vitamin D deficiency. Osteoporosis arises with loss of bone density resulting in brittle bones and fractures. Symptoms of bone pain and muscle weakness may be due to inadequate vitamin D levels. These symptoms can be subtle and go undetected in the initial stages.

Children may suffer from insufficiency if the nursing mothers are deficient in vitamin D. Moreover mother's milk may not contain sufficient vitamin D and unless the children are exposed to sun light and, or supplemented with vitamin D they may develop rickets.

Homebound people and people living in northern latitudes may suffer from the deficiency of this vitamin. Darker skin also may reduce the ability of the skin to produce vitamin D from sun light. However excessive sun exposure to avoid deficiency carry the risk of skin cancer.

Vitamin D deficiency is connected to increase in blood pressure and cardiovascular risk. In dialyses patients low levels of vitamin D can lead to diabetes, hypertension and cancer.

Toxicity
Exposure to extended time does not cause toxicity as the excess produced is degraded. Generally vitamin D toxicity is very rare and its symptoms are nausea, poor appetite, weakness and weight loss.

Sources
Very few foods are natural source of vitamin D. Fish liver oils, liver, cheese and egg are the best sources. For further information please visit http://www.thedynamicnature.com/vitamins/vitamin%20D.html.