Vitamin B3 (Niacin)

Vitamins & Minerals

Last reviewed: April 7, 2026. Source approach: standard laboratory interpretation context, general medical reference material, and public-health or clinical guidance where relevant.

What is Vitamin B3 (Niacin)?

Niacin, also known as vitamin B3 or nicotinic acid, is a water-soluble vitamin that serves as the precursor to nicotinamide adenine dinucleotide (NAD+) and its phosphorylated form NADP+. These coenzymes are involved in over 400 enzymatic reactions in the body, more than any other vitamin-derived coenzyme, making niacin indispensable for energy metabolism, DNA repair, cell signaling, and the synthesis of steroid hormones and fatty acids.

Niacin exists in two main forms: nicotinic acid and nicotinamide (niacinamide). Both forms contribute to NAD+ synthesis, but they have different pharmacological effects—nicotinic acid lowers LDL cholesterol and triglycerides and raises HDL cholesterol, while nicotinamide does not have these lipid-modifying properties. The body can also synthesize niacin from the essential amino acid tryptophan, although this pathway is inefficient (approximately 60 mg of tryptophan produces 1 mg of niacin). Niacin status is typically assessed by measuring urinary N1-methylnicotinamide and its metabolite 2-pyridone, or by measuring NAD levels in red blood cells.

Why It Matters

Niacin is essential for cellular energy production and the maintenance of NAD+ pools, which decline with age and are increasingly recognized as central to healthy aging. Severe niacin deficiency causes pellagra, a potentially fatal condition characterized by the classic "four Ds": dermatitis, diarrhea, dementia, and death. Beyond preventing deficiency, adequate niacin supports cardiovascular health, brain function, and DNA integrity. NAD+ has emerged as a key molecule in longevity research due to its role in activating sirtuins, enzymes that regulate cellular stress responses and metabolism.

Normal Reference Ranges

Group	Range	Unit
Adults (urinary N1-methylnicotinamide)	5.8–35.5	µmol/day
Adults (whole blood NAD)	127–249	µmol/L

Reference ranges may vary by laboratory. Always compare results to the ranges provided by your testing facility.

What High B3 Levels Mean

Common Causes

High-dose niacin supplementation (>1000 mg/day)
Prescription niacin therapy for dyslipidemia
Excessive intake of fortified foods

Possible Symptoms

Flushing (warmth, redness, tingling of face, neck, chest)—most common
Gastrointestinal distress (nausea, vomiting, diarrhea)
Hepatotoxicity (especially with sustained-release formulations)
Hyperglycemia and worsened insulin resistance
Hyperuricemia and gout flares
Pruritus (itching)

What to do: Niacin toxicity from supplements requires immediate dose reduction or discontinuation. Liver function tests should be monitored in anyone taking therapeutic doses (>500 mg/day). Flushing can be mitigated by taking aspirin 30 minutes before the dose, using extended-release formulations, or taking niacin with food. However, sustained-release niacin carries the highest hepatotoxicity risk and should be used cautiously. Consult your doctor before using high-dose niacin for cholesterol management.

What Low B3 Levels Mean

Common Causes

Inadequate dietary intake (diets heavily dependent on untreated corn)
Chronic alcoholism
Carcinoid syndrome (tryptophan diverted to serotonin production)
Hartnup disease (impaired tryptophan absorption)
Medications (isoniazid, 6-mercaptopurine)
Malabsorption disorders
Prolonged use of certain chemotherapy agents

Possible Symptoms

Dermatitis (bilateral, symmetric, on sun-exposed skin—Casal necklace)
Diarrhea and gastrointestinal inflammation
Dementia, confusion, and memory loss
Depression and anxiety
Glossitis (bright red, swollen tongue)
Fatigue and weakness
In severe cases: psychosis and death (pellagra)

What to do: Mild deficiency is treated with 50–100 mg of nicotinamide three times daily, with clinical improvement typically seen within days. Pellagra requires higher doses (300–500 mg daily) along with a well-balanced diet and supplementation of other B vitamins, as deficiencies frequently coexist. Address underlying causes such as alcoholism or malabsorption. Increase dietary intake of niacin-rich foods including poultry, fish, peanuts, mushrooms, and fortified grains.

When Is B3 Testing Recommended?

When pellagra is suspected (dermatitis, diarrhea, dementia)
In chronic alcoholism with nutritional concerns
In patients with carcinoid syndrome
When using isoniazid or other niacin-depleting medications
When evaluating causes of symmetric photosensitive dermatitis
In populations with corn-based diets without nixtamalization

Frequently Asked Questions

Niacin flush is a harmless but uncomfortable side effect of nicotinic acid supplementation. It occurs because nicotinic acid triggers the release of prostaglandin D2 in the skin, causing blood vessel dilation that produces warmth, redness, and tingling, typically in the face, neck, and chest. It usually begins 15–30 minutes after ingestion and lasts 30–60 minutes. The flush is not dangerous and tends to diminish with continued use. Taking aspirin beforehand, using extended-release formulations, or taking niacin with food can reduce its intensity. Nicotinamide does not cause flushing.

Nicotinic acid (not nicotinamide) is one of the most effective agents for raising HDL cholesterol (by 15–35%), while also lowering LDL cholesterol (5–25%) and triglycerides (20–50%). It was the first lipid-modifying agent shown to reduce cardiovascular events in clinical trials. However, recent large trials (AIM-HIGH, HPS2-THRIVE) showed no additional cardiovascular benefit when niacin was added to statin therapy, and it increased side effects. As a result, niacin is now primarily reserved for patients who cannot tolerate statins or who have severely low HDL levels.

Pellagra was historically epidemic in populations whose diets relied heavily on corn (maize). Corn contains niacin primarily in a bound form (niacytin) that is not bioavailable to humans. Additionally, corn is low in tryptophan, the amino acid the body uses to synthesize niacin. The Mesoamerican practice of nixtamalization—soaking corn in lime water—releases the bound niacin and significantly increases its bioavailability, which is why pellagra was rare in indigenous populations but became widespread when corn was adopted in Europe and the American South without this processing technique.

Related Biomarkers

B2Vitamin B2 (Riboflavin)PLPVitamin B6 LDL-CColesterolo LDL HDL-CColesterolo HDL

References and review approach

Biomarker glossary pages are educational explainers and should be interpreted alongside the reference ranges and comments provided by your laboratory and clinician. For our editorial standards and review approach, see our Editorial Policy and Content Review Process.

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Medical Disclaimer: This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Reference ranges may vary between laboratories. Always consult your healthcare provider for interpretation of your specific test results.