To help the body absorb calcium, vitamin D3, also known as cholecalciferol, is important for the body. This supplement is typically used for people who have vitamin D deficiency or similar disorders. The people in those categories include older adults, breastfed babies, people with darker skin, obese individuals, and people with conditions such as Crohn’s disease, cystic fibrosis, or liver disease. It is important to consult with a doctor about supplementing vitamin D3 if allergic reactions have occurred in the past or if the body already has high levels of vitamin D (hypervitaminosis D), high levels of calcium in the blood (hypercalcemia), or malabsorption of nutrients. Side effects may include allergic reactions, growth issues, and chest pain or feelings of shortness of breath. If pregnant, too much vitamin D may harm an unborn baby or a nursing baby, so the dosage may be different during pregnancy. Vitamin D is used to treat or prevent many conditions such as osteoporosis, seasonal affective disorder, psoriasis, or dementia or other cognitive disorders.