Vitamin B3

What Is Niacin (Vitamin B3)?

Niacin is the name for two water-soluble compounds with the same vitamin activity: nicotinic acid and nicotinamide (also sold as niacinamide). Both are turned into nicotinamide adenine dinucleotide (NAD) and its phosphate form, NADP. Despite the names, neither acts like the nicotine in tobacco.

What Niacin Does

More than 400 enzymes need NAD or NADP, more than for any other vitamin-derived coenzyme. NAD carries energy out of carbohydrate, fat and protein; NADP builds fats and cholesterol and keeps the cell's antioxidant systems running. NAD is also used up in repairing DNA and in signals between cells.

Niacin From Tryptophan and Niacin Equivalents

The body can make niacin from tryptophan, an amino acid in protein: about 60 mg of tryptophan gives 1 mg of niacin. Daily needs are set in niacin equivalents (NE) to count both. The conversion also needs riboflavin, vitamin B6 and iron, so a shortage of those slows it down.

Food figures, including the ones on this page, count only the niacin already in the food. Meat, fish, eggs and milk bring tryptophan as well, so they give more niacin equivalents than their figure suggests. Eggs and milk look poor in niacin here, yet the tryptophan in their protein still adds niacin equivalents.

A Day of Food With More Than 16 mg of Niacin

One ordinary day of foods from the Caltide food library, in usual portions, without supplements and without counting tryptophan.

Two foods, chicken breast and tuna, give 66% of it. For people who eat meat or fish, running short of niacin from food alone is rare.

Niacin, Corn, and Pellagra

Most of the niacin in corn is bound in a form the gut cannot use. In Mexico and Central America, corn has long been soaked and cooked in lime water (nixtamalization) to make masa for tortillas, which frees the niacin. Where corn became a staple without that step, as in the southern United States in the early 1900s, pellagra became common, with its rash on sun-exposed skin, diarrhea and confusion.

Today pellagra is rare in richer countries. The people most at risk are those with alcohol use disorder or poor diets, and people with conditions that limit tryptophan, such as Hartnup disease or carcinoid syndrome.

High-Dose Niacin as a Cholesterol Drug

At doses of 1 g a day or more, over 60 times the daily need, nicotinic acid raises HDL cholesterol and lowers LDL and triglycerides. For years it was prescribed for that. Then two large trials, AIM-HIGH and HPS2-THRIVE, found that adding it to a statin did not cut heart attacks or strokes, while it raised side effects. Doses like these are a medical treatment, not a supplement habit.