Vitamin B3: Niacin

Niacin, vitamin B3, is found as nicotinic acid in plant foods and nicotinamide in animal foods.¹ Niacin is active in the body as coenzymes nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP) which are also found in meat products. Niacin, in the form of nicotinic acid, is prescribed to lower cholesterol and triglyceride levels due to its ability to immobilize fatty acids from circulation to prevent VLDL formation.¹

Absorption/Metabolism: NAD and NADP must be converted into nicotinamide before absorption. Nicotinamide and nicotinic acid are absorbed mostly within the small intestine and enter blood plasma bound to protein or free.¹

Within cells, nicotinamide is converted into NAD and then phosphorylated into NADP.¹ Nicotinic acid can also be converted into NAD.¹

Functions: Niacin coenzymes are used throughout energy metabolism in hundreds of redox reactions. Examples include:

NAD is reduced into NADH during the conversion of pyruvate to acetyl CoA, and 3 reactions within the Krebs cycle. The oxidation of fatty acids for energy also creates NADH.

Other than metabolism, niacin is responsible for converting vitamin B6 to pyridoxal acid. NADP is involved in the pentose phosphate pathway which converts glucose 6-phosphate into nucleotides and synthesizes NADPH from NADP.¹ NADPH is used in cholesterol, fatty acid, steroid hormone, and deoxynucleotide synthesis.¹

Niacin plays an important role in mitochondrial health through sirtuins which are proteins found in cells that carry out various enzymatic activities. Sirtuins’ functions and activity are based on the ratio of niacin.¹ 

Dietary Reference Intake (DRI) - The recommended dietary allowance (RDA) for adult men and women over 19 years old is 16 and 14 milligrams/day.²

Deficiency - Niacin deficiency is known as pellagra which is characterized by the ‘4 Ds’: dermatitis, diarrhea, dementia, and death. 

Toxicity - Niacin toxicity may occur through medication or supplement form, causing a variety of symptoms such as heart, GI, and liver issues.¹ 

Dietary Sources of Niacin 

Niacin is found in a variety of foods including grains, fruits, and vegetables but is found highly among meat and dairy products. Niacin is enriched into refined grains after processing due to the loss of B vitamins, including thiamin. It is required by the U.S. government in a legislative act known as the Enrichment Act.¹

Meat -  beef, chicken, salmon

Dairy -  milk, cheese, yogurt 

Fruit/Vegetables - asparagus, potatoes, bananas 

Starches - rice, cereals, bread 

Nuts/seeds - peanuts, sunflower seeds, pumpkin seeds

Source(s):

1. Denise M Medeiros and Robert E.C. Wildman, Advanced Human Nutrition, 4th ed. (Burlington, MA: Jones & Bartlett, 2019).

2. https://ods.od.nih.gov/factsheets/Niacin-HealthProfessional/