What is the purpose of vitamin D3?

Vitamin D3 helps the human body to absorb calcium, and vitamin D3 prescriptions and supplements are often used when a patient has a deficiency that prevents the body from using calcium effectively. It is often used to treat certain conditions affecting the bones or skin, according to Everyday Health.

People who have kidney disease or who suffer from hypoparathyroidism may have to take vitamin D3 in an effort to maintain proper calcium levels and encourage normal bone growth, notes WebMD. Breastfed infants are sometimes given vitamin D3 since breast milk is usually low in this nutrient. This vitamin is best absorbed when taken after a meal, but some forms can be taken without food.