What it does
The NIH consumer sheet says niacin helps turn the food you eat into the energy you need. It also says niacin is important for the development and function of cells. The body can make some niacin from tryptophan, an amino acid in protein.
What research can and cannot say
The sheet says large doses of nicotinic acid can change blood cholesterol numbers, and that those changes did not change the chance of a heart attack or stroke. Prescription-strength nicotinic acid is more than 100 times the recommended dietary allowance. That is a different product from a shopping-label amount.
A niacin label does not show a change in cholesterol or heart risk. Nicotinic acid and nicotinamide are forms. One form's warning does not automatically apply to the other.
Forms and label reading
The two main supplement forms are nicotinic acid and nicotinamide. Nicotinamide is also called niacinamide. Read which form the Supplement Facts panel names. The milligrams may be niacin equivalents (mg NE) or a labeled milligram amount. Read the unit the panel prints.
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.
Amount and upper limit
Recommended amount. The NIH sheet lists 16 mg NE a day for adult men and 14 mg NE a day for adult women. NE means niacin equivalents, which counts niacin from food and niacin the body makes from tryptophan. It lists 18 mg NE for pregnant teens and women and 17 mg NE for breastfeeding teens and women. Cited sheet
Upper limit. The sheet lists 35 mg a day as the upper limit for adults, from dietary supplements. Cited sheet
Safety
The sheet says niacin that food naturally contains is not the problem. Dietary supplements with 30 mg or more of nicotinic acid can make the skin on the face, arms, and chest turn red, burn, tingle, and itch, and can cause headaches, rashes, and dizziness. Doses of 1,000 mg a day or more, taken as medicine, can cause low blood pressure, extreme tiredness, high blood sugar, nausea, heartburn, abdominal pain, and vision problems. Long-term use of extended-release nicotinic acid can cause liver problems. Nicotinamide has fewer of those effects. At 500 mg a day or more it can cause diarrhea and easy bruising, and at 3,000 mg a day or more it can cause nausea, vomiting, and liver damage. The adult upper limit from supplements is 35 mg a day. Tuberculosis drugs such as isoniazid can lower niacin. The sheet also says too little iron, riboflavin, or vitamin B6 makes it harder for the body to make niacin from tryptophan.
Food sources
The sheet names poultry, beef, pork, fish, some nuts, legumes, and grains, and enriched or fortified breads and cereals.