A nutrient that the body needs in small amounts to function and stay healthy. Cholecalciferol helps the body use calcium and phosphorus to make strong bones and teeth. It is fat-soluble (can dissolve in fats and oils) and is found in fatty fish, egg yolks, and dairy products. Skin exposed to sunshine can also make cholecalciferol. Not enough cholecalciferol can cause a bone disease called rickets. It is being studied in the prevention and treatment of some types of cancer. Also called vitamin D.