Niacin

Niacin, also known as vitamin B3, is an essential nutrient that supports energy production, DNA repair, and nervous system function. A blood niacin test measures whether you have adequate levels of this vitamin. Deficiency can cause fatigue, skin problems, and neurological issues, while severe deficiency leads to pellagra. Most people get sufficient niacin from diet, but supplementation may be needed in certain conditions or dietary restrictions.