Niacin Deficiency and Pellagra: The Three Ds and Who Is Affected

Niacin deficiency, when severe enough, causes pellagra, a condition historically linked to populations whose diets relied almost entirely on untreated corn. Today pellagra is rare in high-income countries but still occurs in specific at-risk groups, and understanding why requires a closer look at how the body uses this essential B vitamin.

What Niacin Does in the Body

Niacin, also called vitamin B3, is the precursor to NAD and NADP, two coenzymes that the body uses across more than 400 enzymatic reactions, more than for any other vitamin-derived coenzyme, according to the NIH Office of Dietary Supplements (ODS). That number helps explain why a shortage has such wide-ranging consequences.

In its NAD form, niacin supports the catabolic redox reactions that transfer energy from carbohydrates, fats, and proteins into ATP, the cell's primary energy currency. In its NADP form, it enables anabolic reactions including the synthesis of cholesterol and fatty acids. When niacin is chronically insufficient, these fundamental processes begin to break down, and the clinical result is pellagra.

The Three Ds of Pellagra

Clinicians have long described pellagra through three cardinal signs, each beginning with the letter D.

• Dermatitis. A symmetrical, sun-sensitive rash typically appears on skin exposed to sunlight, including the neck, forearms, and hands. The rash can become scaly, darkened, or cracked over time.
• Diarrhea. Gastrointestinal involvement includes inflammation of the mucous membranes lining the digestive tract, leading to diarrhea, nausea, and abdominal discomfort.
• Dementia. Neurological symptoms range from headache and fatigue to confusion, memory loss, and, in advanced cases, psychosis. The nervous system is particularly sensitive to NAD depletion because neurons depend heavily on oxidative metabolism.

A fourth D, death, is sometimes added to the list to underscore that untreated pellagra is fatal. Adequate niacin intake prevents and reverses pellagra, a finding supported by strong evidence, according to the NIH ODS.

How Much Niacin Do Adults Need?

The NIH ODS reports the following Recommended Dietary Allowances for adults, expressed in niacin equivalents (NE) to account for the fact that the body can convert the amino acid tryptophan into niacin.

• Men aged 19 and older: 16 mg NE per day
• Women aged 19 and older: 14 mg NE per day

These values come from Dietary Reference Intakes established by the National Academies of Sciences, Engineering, and Medicine. The Tolerable Upper Intake Level for supplemental niacin in adults aged 19 and older is 35 mg per day. This limit applies to both nicotinic acid and nicotinamide forms and is based on the risk of skin flushing. It does not apply to people receiving therapeutic niacin under medical supervision. Niacin obtained naturally from foods has no reported adverse effects and carries no upper limit.

Supplements are not intended to diagnose, treat, cure, or prevent any disease, and these statements have not been evaluated by the FDA.

Who Is Most at Risk for Deficiency?

Pellagra is not simply a historical curiosity. Several groups remain at elevated risk today.

People Whose Diets Rely on Untreated Corn

Corn contains niacin in a bound form that the body cannot absorb without alkali processing, a technique called nixtamalization used in traditional Mexican and Central American cooking. Populations that adopted corn as a staple without this processing, as occurred in parts of 18th and 19th century Europe and the American South, developed epidemic pellagra. The same risk persists in regions today where food variety is limited.

People with Alcohol Use Disorder

Heavy alcohol use interferes with the absorption and metabolism of multiple B vitamins, including niacin. Poor dietary intake compounds this effect, making alcohol use disorder one of the most common settings in which pellagra appears in high-income countries.

People Taking Certain Medications

Drug interactions can meaningfully disrupt niacin status. Isoniazid and pyrazinamide, both used to treat tuberculosis and found together in the combination drug Rifater, are structural analogs of niacin. They compete with a vitamin B6-dependent enzyme involved in converting tryptophan to niacin, and isoniazid can also interfere with niacin's conversion to NAD. Pellagra has been documented in patients on tuberculosis therapy unless niacin intake is increased. Anyone taking these medications should speak with their prescribing clinician about monitoring niacin status.

People with Malabsorption Conditions

Conditions that impair nutrient absorption in the small intestine, including Crohn's disease and carcinoid syndrome, can reduce the amount of niacin and tryptophan the body retains from food.

People with Hartnup Disease

This rare inherited disorder impairs the intestinal and renal transport of tryptophan, limiting the body's ability to synthesize niacin from this amino acid. Affected individuals may develop pellagra-like symptoms even when dietary niacin appears adequate.

A Note on High-Dose Niacin and Drug Interactions

Pharmacologic doses of nicotinic acid in the thousands of milligrams per day are used medically to manage dyslipidemia. At these doses, nicotinic acid raises HDL cholesterol and lowers LDL cholesterol, triglycerides, and lipoprotein(a), evidence the NIH ODS rates as strong. However, evidence that nicotinic acid supplementation reduces the risk of cardiovascular events is currently rated as insufficient by the NIH ODS.

These doses act as a drug, not a supplement, and carry meaningful risks. Large doses of nicotinic acid, at 1.5 g per day or more, can raise blood glucose by causing or worsening insulin resistance and increasing hepatic glucose production. People taking antidiabetes medications who also use high-dose nicotinic acid may need blood glucose monitoring and medication adjustments. Anyone considering high-dose niacin therapy should do so only under physician supervision. Always talk to a doctor or pharmacist before combining any supplement with prescription medication.

Getting Enough Niacin from Food

For most people eating a varied diet, meeting the daily niacin target is straightforward. Good dietary sources include poultry, beef, fish, peanuts, whole grains, and fortified cereals. Because niacin from food carries no adverse effects and no upper limit, food-first approaches are generally preferred over supplementation for healthy adults without a diagnosed deficiency.

If you have concerns about your niacin status or fall into one of the at-risk groups described above, consult a clinician or registered dietitian for a personal assessment. Do not adjust supplement doses or combine supplements with medication without professional guidance.

Sources

• NIH Office of Dietary Supplements, Niacin Fact Sheet for Health Professionals: https://ods.od.nih.gov/factsheets/Niacin-HealthProfessional/
• NIH Office of Dietary Supplements, Niacin Fact Sheet for Consumers: https://ods.od.nih.gov/factsheets/Niacin-Consumer/
• National Academies of Sciences, Engineering, and Medicine, Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline (1998): https://nap.nationalacademies.org/catalog/6015/