Niacin. Coloured scanning electron micrograph (SEM) of crystals of niacin, also known as nicotinic acid and vitamin B3. Niacin is part of the B vitamin complex and so an essential nutrient. It takes part in many metabolic reactions. It is required for normal digestive function and also helps to reduce LDL, or bad, cholesterol secretion from the liver. Dietary sources of niacin include cheese, milk, meat, poultry, fish, eggs and whole grains. A deficiency of niacin can cause pellagra, with symptoms including mental confusion, diarrhoea and dermatitis. Magnification: x160 when printed at 10 centimetres wide.