Update in D hormone

Humans depend on sun-exposure for their vitamin D requirements. Solar ultraviolet B photons are absorbed by 7 dihydroxycholecalciferol in the skin leading to its conversion to previtamin D3, which is rapidly converted to vitamin D3. Season, latitude, time of day, skin pigmentation, aging, customary clothing, sunscreen use, glass, obesity all influence the cutaneous production of VD3. Once formed, VD3 is metabolized in the liver to 25OHD3 and then in the kidney to its biologically active form 1,25(OH)2D3. Vitamin D deficiency causes osteoporosis and also bone disease ışıostemalacia among adults, rickets among children. Vitamin D deficiency also has been associated with increased risks of many autoimmune dieases such as multiple sclerosis, rheumatoid arhritis, and type 1 diabetes, besides cardiovascular disease, metabolic syndrome and cancers. It is also suggested that vitamin D deficiency related to accelerated aging, and longevity of the life span. Serum 25OHD3 levels is the best reflection of the vitamin D status. Maintaining blood concentrations of 25OHD3 above 30 ng/mL, and 20-29 ng/mL is accepted as vitamin D sufficiency and insufficiency respectively. The levels below 20 ng/mL defines vitamin deficiency. The nuclear vitamin D receptors not only present in kidney, bone, parathyroid gland and intestine, which are known to be the main target tissues of vitamin D, but also in wide variety of other tissues. The low levels of vitamin D is important for maximizing calcium absorption from intestine, but it is also important for providing the production of extrarenal 1,25(OH)2D3 which has paracrine or autocrine role as a cytokine, to protect the inside environment of the host by modulating the immune responses. The avoidance of direct sun exposure, increases the risk of vitamin D deficiency, which can have serious consequences. Monitoring serum 25OHD3 concentrations yearly, should help reveal vitamin D deficiencies. Sensible sun exposure (usually 10-20 minutes of exposure of the arms, legs and face 3-4 times a week), or increase in dietary intake of vitamin D prevents deficiency. The recommendation of supplemental daily intakes of vitamin D 1000 IU or in selected persons (elderly) 2000 IU are reasonable approaches to guarantee vitamin D sufficiency.