Vitamin D

Vitamin D is a fat-soluble vitamin that is naturally present in very few foods, added to others, and available as a dietary supplement. 

It is also produced endogenously when ultraviolet rays from sunlight strike the skin and trigger vitamin D synthesis. 

Vitamin D obtained from sun exposure, food, and supplements is biologically inert and must undergo two hydroxylations in the body for activation. 

The first occurs in the liver and converts vitamin D to 25-hydroxyvitamin D [25(OH)D], 
also known as calcidiol. 
The second occurs primarily in the kidney and forms the physiologically active 1,25-dihydroxyvitamin D [1,25(OH)2D], also known as calcitriol.

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. 

Without sufficient vitamin D, bones can become thin, brittle, or misshapen. Vitamin D sufficiency prevents rickets in children and osteomalacia in adults. Together with calcium, vitamin D also helps protect older adults from osteoporosis.

Notes;  

hypocalcemic tetany : A condition that is due usually to low blood calcium (hypocalcemia) and is characterized by spasms of the hands and feet, cramps, spasm of the voice box (larynx), and overactive neurological reflexes. Tetany is generally considered to result from very low calcium levels in the blood.

 osteoblasts :a cell which secretes the substance of bone.

 osteoclasts :a large multinucleate bone cell which absorbs bone tissue during growth and healing

rickets :a disease of children caused by vitamin D deficiency, characterised by imperfect calcification, softening, and distortion of the bones typically resulting in bow legs.

osteomalacia : softening of the bones, typically through a deficiency of vitamin D or calcium.

osteoporosis : a medical condition in which the bones become brittle and fragile from loss of tissue, typically as a result of hormonal changes, or deficiency of calcium or vitamin D.

 Vitamin D has other roles in the body, including modulation of cell growth, neuromuscular and immune function, and reduction of inflammation.

Simple Vitamin D deficiency can be prevented by taking an oral supplement of only 10 mcg of ergocalcifero (Vitamin D2) or colecalsiferol (Vitamin D3) daily.

Vitamin D deficiency can occur in people whose exposure ti sunlight is limited and those whose diet deficient in vitamin D.
In these individuals, ergocalciferol or colecalciferol in a dose of 20 micro grams daily by mouth may be given to treat vitamin D deficiency. Higher Doses may be necessary for sever deficiency.

Preparations containing Calcium with colecalciferol are available for the management of combined calcium and vitamin D deficiency, or those at high risk of deficiency (Eg; Osteoporosis).

Vitamin D deficiency caused by intestinal malabsorption or chronic iver diseace usually requires Vitamin D in pharmacological dose,such as ergocalcaemia of hypoparathyrodism often requires doses of up to 2.5 mg daily in order to archive normocalcaemia.

Vitamin D requires hydroxylation by the kidney to its active form, therefore the hydroxylated derivatives alfacalcidol and calcitriol should be prescribed if patients with severe renal impairment require vitamin D therapy.

important;

                 all patients receiving pharmacological doses of vitamin D  should have their plasma-calcium concentration checked at intervals (initially once or twice weekly) and whenever nausea or vomiting occur.