Vitamin D3, a chemical compound
Cholecalciferol, also known as vitamin D3, colecalciferol or calciol, is a skin-made vitamin D that is found in certain foods and used as a dietary supplement. It was first described in 1936, and is on the World Health Organization's List of Essential Medicines. In 2023, it was the 68th most commonly prescribed medication in the United States, with more than 9million prescriptions, and is available as a generic medication.
It is synthesised in the skin following sunlight exposure. It is then converted in the liver to calcifediol (25-hydroxycholecalciferol D), which is further converted in the kidney to calcitriol (1,25-dihydroxycholecalciferol D). One of calcitriol's most important functions is to promote calcium uptake by the intestines. Cholecalciferol is present in food such as fatty fish, beef liver, eggs, and cheese. In some countries, cholecalciferol is also added to products like plants, cow milk, fruit juice, yogurt, and margarine.
Cholecalciferol can be taken orally as a dietary supplement to prevent vitamin D deficiency or as a medication to treat associated diseases, including rickets. It is also used in the management of familial hypophosphatemia, hypoparathyroidism that is causing low blood calcium, and Fanconi syndrome. Vitamin-D supplements may not be effective in people with severe kidney disease. Excessive doses in humans can result in vomiting, constipation, muscle weakness, and confusion. Other risks include kidney stones. Doses greater than 40000IU (1000μg) per day are generally required before high blood calcium occurs. Normal doses, 800–2000IU per day, are safe in pregnancy.