Cholecalciferol, also known as vitamin D3 and colecalciferol, is a type of vitamin D which is made by the skin when exposed to sunlight; it is also found in some foods and can be taken as a dietary supplement.Cholecalciferol is made in the skin following UVB light exposure. It is converted in the liver to calcifediol (25-hydroxyvitamin D) which is then converted in the kidney to calcitriol (1,25-dihydroxyvitamin D). One of its actions is to increase the uptake of calcium by the intestines. It is found in food such as some fish, beef liver, eggs, and cheese. Certain foods such as milk, fruit juice, yogurt, and margarine also may have cholecalciferol added to them in some countries including the United States.Cholecalciferol can be taken as an oral dietary supplement to prevent vitamin D deficiency or as a medication to treat associated diseases, including rickets. It is also used for 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, weakness, and confusion. Other risks include kidney stones. Doses greater than 40,000 IU (1,000 μg) per day are generally required before high blood calcium occurs. Normal doses, 800–2000 IU per day, are safe in pregnancy.Cholecalciferol was first described in 1936. It is on the World Health Organization's List of Essential Medicines. Cholecalciferol is available as a generic medication and over the counter. Cholecalciferol is also used at much higher doses to kill rodents.