[1][3] NAD is required for human life and people are unable to make it within their bodies without either vitamin B3 or tryptophan.

[1][8][9] Nicotinamide is recommended as a treatment for niacin deficiency because it can be administered in remedial amounts without causing the flushing, considered an adverse effect.

[15] The term niacin was then adopted internationally by multiple institutions (WHO/FAO,[16] EFSA,[17] FDA,[18] Anvisa[19]) using a broader meaning including all dietary NAD precursors that can prevent signs of deficiency.

NAD also plays a critical role in human metabolism, acting as a coenzyme in both glycolysis and the Krebs cycle.

[23] Severe vitamin B3 deficiency in the diet causes the disease pellagra, characterized by diarrhea, sun-sensitive dermatitis involving hyperpigmentation and thickening of the skin (see image), inflammation of the mouth and tongue, delirium, dementia, and if left untreated, death.

[6] Common psychiatric symptoms include irritability, poor concentration, anxiety, fatigue, loss of memory, restlessness, apathy, and depression.

[24] The biochemical mechanisms for the observed deficiency-caused neurodegeneration are not well understood, but may rest on: A) the requirement for nicotinamide adenine dinucleotide (NAD+) to suppress the creation of neurotoxic tryptophan metabolites; B) inhibition of mitochondrial ATP generation resulting in cell damage; C) activation of the poly (ADP-ribose) polymerase (PARP) pathway, as PARP is a nuclear enzyme involved in DNA repair, but in the absence of NAD+ can lead to cell death; D) reduced synthesis of neuro-protective brain-derived neurotrophic factor or its receptor tropomyosin receptor kinase B; or, E) changes to genome expression directly due to the niacin deficiency.

[1] A cooking technique called nixtamalization, that is, pretreating with alkali ingredients, increases the bioavailability of niacin during maize meal or flour production.

For treating deficiency, the World Health Organization (WHO) recommends administering nicotinamide instead of nicotinic acid, to avoid the flushing side effect commonly caused by the latter.

Oral nicotinic acid or nicotinamide is given as a treatment for this condition in doses ranging from 50 to 100 mg twice a day, with a good prognosis if identified and treated early.

[28] Niacin synthesis is also deficient in carcinoid syndrome, because of metabolic diversion of its precursor tryptophan to form serotonin.

[5] Erythrocyte nicotinamide adenine dinucleotide (NAD) concentrations potentially provide another sensitive indicator of niacin depletion, although definitions of deficient, low and adequate have not been established.

[5][34] For U.S. food and dietary supplement labeling purposes, the amount in a serving is expressed as a percent of Daily Value (%DV).

[1] Among whole food sources with the highest niacin content per 100 grams: Vegetarian and vegan diets can provide adequate amounts if products such as nutritional yeast, peanuts, peanut butter, tahini, brown rice, mushrooms, avocado and sunflower seeds are included.

Face, arms and chest skin turns a reddish color because of vasodilation of small subcutaneous blood vessels, accompanied by sensations of heat, tingling and itching.

[1] At daily doses of nicotinic acid as low as 30 mg, flushing has been reported, always starting in the face and sometimes accompanied by skin dryness, itching, paresthesia, and headache.

[48] In northern Italy it was named pellagra from the Lombard language (agra = holly-like or serum-like; pell = skin).

[10] In the late 1930s, studies by Tom Douglas Spies, Marion Blankenhorn, and Clark Cooper confirmed that niacin cured pellagra in humans.

[55] In 1942, when flour enrichment with nicotinic acid began, a headline in the popular press said "Tobacco in Your Bread."

Carpenter found in 1951, that niacin in corn is biologically unavailable and can be released only in very alkaline lime water of pH 11.

This explains why a Latin-American culture that used alkali-treated (nixtamalized) cornmeal to make tortilla was not at risk for niacin deficiency.