Niacin (nicotinic acid) in large amounts is sometimes used to lower low-density lipoprotein (LDL) cholesterol and triglyceride levels and to increase high-density lipoprotein (HDL) cholesterol levels. Symptoms may include flushing and, rarely, hepatotoxicity.
Niacin (nicotinic acid, nicotinamide) derivatives include nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP), which are coenzymes in oxidation-reduction reactions. They are vital in cell metabolism.
(See also Overview of Vitamins and table Sources, Functions, and Effects of Vitamins.)
Immediate- and sustained-release preparations of niacin (but not nicotinamide) may affect lipid levels. However, whether niacin reduces risk of coronary artery disease and stroke is unclear.
At intermediate doses (1000 mg/day), niacin has the following effects:
Triglyceride levels decrease 15 to 20%.
HDL cholesterol levels increase 15 to 30%.
LDL cholesterol levels decrease < 10%.
Higher doses of niacin (3000 mg/day) reduce LDL cholesterol 15 to 20% but may cause jaundice, abdominal discomfort, blurred vision, worsening of hyperglycemia, and precipitation of preexisting gout. People with a liver disorder probably should not take high-dose niacin.
Flushing, which is prostaglandin-mediated, is more common with immediate-release preparations. It may be more intense after alcohol ingestion, aerobic activity, sun exposure, and consumption of spicy foods. Flushing is minimized if niacin is taken after meals or if aspirin (325 mg, which may work better than lower doses) is taken 30 to 45 minutes before niacin. The chance of severe flushing can be reduced by starting immediate-release niacin at a low dose (eg, 50 mg 3 times a day) and increasing it very slowly.
Hepatotoxicity may be more common with some sustained-release preparations. Some authorities recommend checking levels of uric acid, blood glucose, and plasma aminotransferases every 6 to 8 weeks until the dose of niacin has been stabilized.