Functions

Because of its fundamental role in metabolism, niacin may play an important role in mechanisms for DNA repair and gene stability. Nam, the amide form, participates in the cellular energy metabolism that directly affects normal physiology, influences oxidative stress, and modulates multiple pathways tied to both cellular survival and death; it is a robust cytoprotectant that holds great potential for multiple disease entities.It may have roles in Alzheimer disease, Parkinson disease, aging, diabetes, cancer, and cerebral ischemia.

Sources

Significant amounts of niacin are found in many foods; lean meats, poultry, fish, peanuts, and yeasts are particularly rich sources. Milk and eggs contain small amounts of niacin, but they are excellent sources of tryptophan, giving them significant NE contents.

Deficiency

Niacin deficiency begins with muscular weakness, anorexia, indigestion, and skin eruptions. Severe deficiency of niacin leads to pellagra, which is characterized by dermatitis, dementia, and diarrhea (“the three Ds”); tremors; and a beefy red, sore tongue. The dermatologic changes are usually the most prominent. Skin that has been exposed to the sun develops cracked, pigmented, scaly dermatitis. Central nervous system involvement symptoms include confusion, disorientation, and neuritis. Digestive abnormalities cause irritation and inflammation of the mucous membranes of the mouth and the GI tract. Untreated pellagra can cause death, which is often referred to as “the fourth D.”

Toxicity

In general, niacin toxicity is low. However, high doses of 1 to 2 g of NA three times per day—dosages that have been used in attempts to lower blood cholesterol concentration can have untoward side effects.The main side effect is a histamine release that causes flushing and may be harmful to those with asthma or peptic ulcer disease. Nam does not have this effect. High doses of niacin can also be toxic to the liver; risks are greater with time­released forms of the vitamin. Megavitamin use should be monitored carefully because high doses act as drugs and not nutritional supplements.

DRI Range
2-18 mg/day, depending on age and gender