[6][7] In some countries, cholecalciferol is also added to products like plants, cow milk, fruit juice, yogurt, and margarine.

[6][7] Cholecalciferol can be taken orally as a dietary supplement to prevent vitamin D deficiency or as a medication to treat associated diseases, including rickets.

[11] Doses greater than 40000 IU (1000 μg) per day are generally required before high blood calcium occurs.

[19] Cholecalciferol is a form of vitamin D which is naturally synthesized in skin and functions as a pro-hormone, being converted to calcitriol.

Dietary reference intake values for vitamin D (ergocalciferol, which is D2, or cholecalciferol, which is D3), or both, have been established and recommendations vary depending on the country: Low levels of vitamin D3 are more commonly found in individuals living in northern latitudes or with other reasons for a lack of regular sun exposure, including being housebound, frail, elderly, or obese, having darker skin, and wearing clothes that cover most of the skin.

[25] Patients with severe vitamin D deficiency will require treatment with a loading dose; its magnitude can be calculated based on the actual serum 25-hydroxy-vitamin D level and body weight.

[26] There are conflicting reports concerning the relative effectiveness of cholecalciferol (D3) versus ergocalciferol (D2), with some studies suggesting less efficacy of D2, and others showing no difference.

There are differences in absorption, binding and inactivation of the two forms, with evidence usually favoring cholecalciferol in raising levels in blood, although more research is needed.

[31] A meta-analysis of 2007 concluded that daily intake of 1000 to 2000 IU/d of vitamin D3 could reduce the incidence of colorectal cancer with minimal risk.

[43] In a process which is independent of UV light, the pre-cholecalciferol then undergoes a [1,7] antarafacial sigmatropic rearrangement[44] and therein finally isomerizes to form vitamin D3.

The active UVB wavelengths are little present in sunlight, and sufficient amounts of cholecalciferol can be produced with moderate exposure of the skin, depending on the strength of the sun.

[42] Time of day, season, latitude, and altitude affect the strength of the sun, and pollution, cloud cover or glass all reduce the amount of UVB exposure.

Some unwanted isomers are formed during irradiation: these are removed by various techniques, leaving a resin which melts at about room temperature and usually has a potency of 25000000 to 30000000 International Units/gram.

[46][47] Cholecalciferol is very sensitive to UV radiation and will rapidly, but reversibly, break down to form supra-sterols, which can further irreversibly convert to ergosterol.

[citation needed] Rodents are somewhat more susceptible to high doses than other species, and cholecalciferol has been used in poison bait for the control of these pests.

[48][18] The mechanism of high dose cholecalciferol is that it can produce "hypercalcemia, which results in systemic calcification of soft tissue, leading to kidney failure, cardiac abnormalities, hypertension, CNS depression, and GI upset.