Niasine, commonly known as niacin or vitamin B3, is a water-soluble vitamin that plays a crucial role in energy metabolism and the functioning of the nervous system. It is essential for converting food into energy and is involved in the synthesis of fatty acids and cholesterol. Niacin can be obtained from dietary sources such as meat, fish, whole grains, and legumes, and is also available as a dietary supplement. Deficiency in niacin can lead to conditions like pellagra, characterized by symptoms such as dermatitis, diarrhea, and dementia.