25hidroxivitamin

25-hydroxyvitamin D, also known as calcidiol, is the major circulating form of vitamin D in the blood. It is produced in the liver by the enzyme 25-hydroxylase, which adds a hydroxyl group to the 25th carbon of vitamin D. Vitamin D itself can be obtained from sunlight exposure to the skin or from dietary sources. Once in the liver, vitamin D undergoes hydroxylation to become 25-hydroxyvitamin D. This form is relatively stable and has a long half-life, making it the best indicator of an individual's vitamin D status.

The primary role of 25-hydroxyvitamin D is as a precursor to the active hormonal form of vitamin D, 1,25-dihydroxyvitamin D (calcitriol). This conversion occurs primarily in the kidneys, where another hydroxyl group is added by the enzyme 1-alpha-hydroxylase. Calcitriol then functions as a hormone, regulating calcium and phosphate absorption in the intestines, reabsorption in the kidneys, and bone mineralization. Low levels of 25-hydroxyvitamin D can indicate vitamin D deficiency, which can lead to impaired calcium absorption, bone softening diseases like rickets in children and osteomalacia in adults, and may be associated with an increased risk of other health issues. Conversely, very high levels can indicate vitamin D intoxication. Measurement of 25-hydroxyvitamin D in blood serum is the standard clinical method for assessing vitamin D sufficiency.