Niacin is one of the 8 B vitamins (B3) and is needed by every part of the body for proper function. It is a major component of NAD and NADP, two coenzymes that are involved in cellular metabolism. Niacin also plays a role in cell signaling and making and repairing DNA, in addition to acting as an antioxidant. (https://ods.od.nih.gov/factsheets/Folate-HealthProfessional/).
As a supplement niacin can help lower cholesterol, ease arthritis and boost brain function.
Although it is water-soluble, if taken in large doses at once it can have serious side effects. Nicotinic acid is the form of niacin that is used in combination with restricted cholesterol and fat in the diet to treat high cholesterol and heart disease. (https://www.ncbi.nlm.nih.gov/pubmed/18375237). Nicotinamide or niacinamide can help treat type 1 diabetes, schizophrenia and some skin conditions. (https://www.ncbi.nlm.nih.gov/pubmed/15132730).
Niacin can be used in a number of situations including the following:
alone or in combination with other medications, such as HMG-CoA inhibitors (statins) or bile acid-binding resins;
to decrease the risk of another heart attack in patients with high cholesterol who have had a heart attack;
to prevent worsening of atherosclerosis (buildup of cholesterol and fats along the walls of the blood vessels) in patients with high cholesterol and coronary artery disease;
to reduce the amounts of triglycerides (other fatty substances) in the blood in patients with very high triglycerides who are at risk of pancreatic disease (conditions affecting the pancreas, a gland that produces fluid to break down food and hormones to control blood sugar).
Niacin is also used to prevent and treat pellagra (niacin deficiency), a disease caused by inadequate diet and other medical problems.
Results of a clinical study in people with heart disease and well-controlled cholesterol levels that compared people who took niacin and simvastatin with people who took simvastatin alone and found similar results for the two groups in the rate of heart attacks or strokes. Taking niacin along with simvastatin or lovastatin also has not been shown to reduce the risk of heart disease or death compared with the use of niacin, simvastatin, or lovastatin alone. (https://www.hindawi.com/journals/isrn/2013/168504/).