The absorption of niacin occurs in the intestines and stomach through active and passive transport, as Georgia Highlands College explains. Niacin is then carried to the liver, where it is converted into the coenzymes nicotinamide adenine dinucleotide, or NAD, and nicotinamide adenine diculeotide phosphate, or NADP. The coenzymes NAD and NAPD play a central role in energy metabolism.
Niacin, or vitamin B3, facilitates the conversion of carbohydrates into glucose, which is used by the body to create energy. Niacin likewise aids the body in using protein and fats, as University of Maryland Medical Center describes. Niacin is necessary for healthy skin, eyes and hair. It also helps keep the liver and nervous system healthy and functional.
Niacin is present in a variety of foods, including meat, fish, eggs and milk, as detailed by MedlinePlus. It is also found in green vegetables, yeast, cereal grains and beans. Niacin is likewise available in vitamin B complex supplements.
Individuals who suffer from a mild niacin deficiency may experience fatigue, indigestion and vomiting, according to WebMD. Severe niacin deficiency, or pellagra, can affect the skin, nervous system and digestive system. Pellagra's symptoms include headache; diarrhea; swollen mouth; a bright red tongue; and thick, scaly pigmented skin rashes. People with pellagra may also develop depression, disorientation, memory loss and apathy. If left untreated, severe niacin deficiency can lead to death.