A nutrient in the vitamin B complex that the body needs in small amounts to function and stay healthy. Vitamin B3 helps some enzymes work properly and helps skin, nerves, and the digestive tract stay healthy. Vitamin B3 is found in many plant and animal products. It is water-soluble (can dissolve in water) and must be taken in every day. Not enough vitamin B3 can cause a disease called pellagra (a condition marked by skin, nerve, and digestive disorders). A form of vitamin B3 is being studied in the prevention of skin and other types of cancer. Vitamin B3 may help to lower blood cholesterol. Also called niacin and nicotinic acid.