DRI: 600 IU/day (15 mcg equivalent)
Tolerable upper intake levels: 4000 IU
LRNI: No report.
Several form of vitamin D exist. The two major forms are vitamin D2 or ergocalciferol, and vitamin D3 or cholecalciferol, These are known collectively as calciferol. Chemically, the various forms of vitamin D are steroids.
Vitamin D3 : produced by ultraviolet irradiation (UV) of its precursor 7-dehydrocholesterol. This molecule occurs naturally in the skin of animals and in milk. Vitamin D3 can be made by exposure of the skin to UV, or by exposing milk directly to UV .Vitamin D2 is a derivative of ergosterol, a membrane sterol named for the ergot fungus, which is produced by some organisms of phytoplankton, invertebrates, and fungi. Catfish,Salmon, Mackerel, Sardines, Tuna, Eel, egg, Beef liver,Fish liver oils, UV-irradiated mushrooms and UV-irradiated yeast.
Mechanism of action:
Vitamin D promotes calcium absorption in the gut and maintains adequate serum calcium and phosphate concentrations to enable normal mineralization of bone and to prevent hypocalcemic tetany. It is also needed for bone growth and bone remodeling by osteoblasts and osteoclasts.
It is absorbed in small intestine.
- Vitamin D in low levels is a common risk factor for osteoarthritis and its progression. The most important function of vitamin D is to maintain normal blood levels of calcium and phosphorus.
- Vitamin D aids in the absorption of calcium, helping to form and maintain strong bones.
- Vitamin D provides protection from osteoporosis, hypertension (high blood pressure), cancer, and several autoimmune diseases.
- Vitamin D has other roles in the body, including modulation of cell growth, neuromuscular and immune function, and reduction of inflammation. Many genes encoding proteins that regulate cell proliferation, differentiation, and apoptosis are modulated in part by vitamin D.
- Without sufficient vitamin D, bones can become thin, brittle, or misshapen.
- Vitamin D is essential for the processing of calcium and the maintenance of healthy bones and joints. In addition, vitamin D can stimulate the synthesis of proteoglycan, which is an important component of joint cartilage.
Rickets, Osteomalacia, a bone-thinning disorder that occurs exclusively in adults and is characterized by proximal muscle weakness and bone fragility.