Cholecalciferol

Cholecalciferol, also known as vitamin D3, is a fat-soluble secosteroid essential for calcium and phosphate metabolism. It is produced in the skin from 7-dehydrocholesterol upon exposure to ultraviolet B radiation and is found in certain animal-derived foods, fortified products, and dietary supplements.

After absorption, cholecalciferol is transported to the liver, where it is hydroxylated to 25-hydroxycholecalciferol (calcidiol), the major circulating form used to assess vitamin D status. In the kidney, calcidiol is further hydroxylated by 1-α-hydroxylase to the physiologically active 1,25-dihydroxycholecalciferol (calcitriol), a hormone that regulates calcium and phosphate homeostasis.

Calcitriol increases intestinal absorption of calcium and phosphate, supports bone mineralization, and influences bone remodeling. Deficiency in children causes rickets, while deficiency in adults leads to osteomalacia; low vitamin D status is also associated with increased osteoporosis risk and fractures.

Cholecalciferol is used to prevent or treat vitamin D deficiency and to maintain adequate stores in individuals at risk, such as those with limited sun exposure, older adults, or malabsorption syndromes. It is available in oral capsules or liquids and, in some cases, by intramuscular injection. Being fat-soluble, it is stored in adipose tissue and can accumulate with prolonged high-dose intake.

Excessive supplementation can cause hypercalcemia and related symptoms. The tolerable upper intake level for adults is 4,000 IU (100 µg) per day, though higher doses may be used under medical supervision for short periods. Drug interactions and conditions affecting vitamin D metabolism can influence dosing and safety.