Vitamin B3, or niacin, is a B vitamin that the body uses to convert food into energy and store it. It also aids the function of nerves and promotes the health of the skin, tissues, and digestive system. Niacin is found in milk, eggs, canned tuna, lean meats, fish, peanuts, legumes, and poultry. You can find niacin in milk, eggs, rice, lean meats, peanuts, poultry, legumes, and enriched cereals and breads. A deficiency in vitamin B3 is called pellagra. Symptoms of the condition include mental problems, dementia, digestive problems, and dermatitis. As a supplement, normal or large doses of niacin may produce flushing that includes redness, a feeling of warmth on the skin, and itching or tingling in the face, arms, neck, or upper chest. Avoid drinking alcohol and drinking hot beverages when you take niacin because it can make flushing worse. Newer forms of the vitamin (nicotinic acid and nicotinamide) minimize or eliminate flushing altogether.