Niacin helps to lower levels of LDL cholesterol, often called "bad" cholesterol, in the body and raise levels of HDL, or "good," cholesterol. Niacin, or vitamin B3, is also used to treat conditions like type 1 and type 2 diabetes.
Niacin has also shown some promise in treating Alzheimer's disease and lowering the risk of a second heart attack in men who suffer from cardiovascular disease. Niacin is also taken to treat mental conditions like attention deficit-hyperactivity disorder and depression, though its efficacy is uncertain. As a B vitamin, niacin works best with the other B vitamins to help the body turn nutrients into fuel.