Niacin, or vitamin B3, is a water-soluble B vitamin found naturally in some foods, added to foods, and sold as a supplement. The two most common forms of niacin in food and supplements are nicotinic acid and nicotinamide. The body can also convert tryptophan—an amino acid—to nicotinamide. Niacin is water-soluble so that excess amounts the body does not need are excreted in the urine. Niacin works in the body as a coenzyme, with more than 400 enzymes dependent on it for various reactions. Niacin helps to convert nutrients into energy, create cholesterol and fats, create and repair DNA, and exert antioxidant effects. [1,2]
Recommended Amounts
RDA: Niacin is measured in milligrams (mg) of niacin equivalents (NE). One NE equals 1 milligram of niacin or 60 mg of tryptophan. The Recommended Dietary Allowance (RDA) for adults 19+ years is 16 mg NE for men, 14 mg NE for women, 18 mg NE for pregnant women, and 17 mg NE for lactating women.
UL: The Tolerable Upper Intake Level is the maximum daily intake unlikely to cause harmful effects on health. The UL for niacin for all adults 19+ years is 35 milligrams.
Niacin and Health
Cardiovascular disease
For more than 40 years, niacin in the form of nicotinic acid has been given to patients to treat a condition called dyslipidemia, a major risk factor for cardiovascular diseases (CVD) such as coronary artery disease, heart attack, and strokes. Bloodwork in someone with dyslipidemia may show high total and LDL “bad” cholesterol levels, low HDL “good” cholesterol, and elevated triglycerides.
Nicotinic acid supplements contain high amounts, up to 1,000-2,000 mg of niacin taken daily. Studies have shown that they can increase HDL cholesterol and lower LDL cholesterol and triglycerides. However, negative side effects (skin flushing, stomach upset, diarrhea) usually accompany the supplements, resulting in poor compliance from patients. Clinical trials have not consistently shown that nicotinic acid leads to less cardiovascular events or deaths from CVD.
Though earlier clinical trials showed a reduction in CVD events and deaths with niacin therapy, two more recent large clinical trials on CVD outcomes concluded differently. [3,4] Both were large randomized placebo-controlled trials, following participants for up to 4 years. Niacin supplements were given (1,500-2,000 mg daily), alone in one trial and with a statin medication in the other. Both trials concluded that taking niacin supplements did not show benefit. The niacin/statin trial did not show a reduction in strokes, heart attack, or CVD deaths despite significant improvements in HDL cholesterol and triglyceride levels. [3] The niacin supplement-only trial did not find a reduction in CVD events and also noted a significant increase in adverse reactions compared with the placebo group, including increased incidence of type 2 diabetes, gastrointestinal bleeding and ulcers, and diarrhea. [4]
A Cochrane review of 23 randomized controlled trials on nicotinic acid supplements for the prevention of CVD events found that the supplements did not reduce overall deaths, CVD deaths, heart attacks, and strokes, and was associated with negative side effects. [5]
The results of these and other cardiovascular outcome trials led the U.S. Food and Drug Administration (FDA) to conclude that the “scientific evidence no longer supports the conclusion that a drug-induced reduction in triglyceride levels and/or increase in HDL-cholesterol levels in statin-treated patients results in a reduction in the risk of cardiovascular events.” [6] Along with that conclusion, the FDA stated that the benefits of niacin extended-release tablets and fenofibric acid capsules taken with statins no longer outweighed the risks, and should not be recommended.
Cognitive health
A severe niacin deficiency has been associated with cognitive decline such as memory loss and dementia. Niacin is believed to protect brain cells from stress and injury. It is not yet clear though if smaller variations in dietary niacin intake can negatively affect brain function.
A large prospective study of 3,718 men and women ages 65 and older were followed for 6 years, using dietary questionnaires and cognitive assessments. [7] A protective effect from Alzheimer’s disease and cognitive decline was found when comparing the highest to lowest intakes of niacin.
The Coronary Artery Risk Development in Young Adults (CARDIA) study followed 3,136 men and women ages 18-30 for up to 25 years. [8] The study measured dietary and supplemental B vitamin intake and cognitive function. A higher intake of B vitamins, but particularly niacin, throughout young adulthood was associated with better cognitive function scores in midlife. However, cognitive function was only assessed at the end of the study, so any changes in cognitive function over time was not known.
Research in this area is limited but there are several clinical trials underway that may shed further light on niacin’s effects on brain health. [9]
