Niacin (Vitamin B3): What It Does and Why You Need It

A B vitamin your cells cannot make energy without, and one of the few nutrients with an actual drug version.

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By the Ration Editorial Team · Reviewed against primary research · Updated July 14, 2026

Niacin is vitamin B3, one of the eight B vitamins your body needs from food on a regular basis.

It exists in two main forms: nicotinic acid and nicotinamide (also called niacinamide). Both count toward your niacin intake, but they behave differently at high doses.

Your body can also make a small amount of niacin from the amino acid tryptophan, which is found in protein-rich foods.

Niacin is the building block for two coenzymes, NAD and NADP, that are involved in hundreds of metabolic reactions.

These coenzymes help cells convert carbohydrates, fats, and protein into energy. They also play roles in DNA repair and cell signaling.

Because nearly every cell relies on NAD to function, niacin is considered essential for basic metabolism, not just a nice-to-have nutrient.

Severe niacin deficiency causes a disease called pellagra, historically marked by the '4 D's': dermatitis, diarrhea, dementia, and death if untreated.

Pellagra was common in the early 1900s in populations eating mostly corn, which is low in usable niacin and tryptophan. Fortification of flour and grain products in many countries has made it rare today.

Mild deficiency can still show up as fatigue, mouth sores, or skin changes, particularly in people with alcohol use disorder, malabsorption conditions, or very restrictive diets.

Niacin is widespread in the food supply, especially in animal proteins and fortified grains.

• Poultry, such as chicken and turkey breast
• Tuna and other fish
• Beef and pork
• Peanuts and peanut butter
• Brown rice and whole grains
• Fortified breakfast cereals and enriched bread
• Mushrooms
• Coffee, which contributes small amounts

At doses far above what you get from food, prescription-strength nicotinic acid has been used for decades to raise HDL cholesterol and lower LDL cholesterol and triglycerides.

However, later large trials testing niacin added on top of statins did not show additional reduction in heart attacks or strokes, and raised concerns about side effects. This shifted niacin out of favor as a routine addition to statin therapy in most guidelines.

This distinction matters: getting normal amounts of niacin from food supports everyday metabolism, while high-dose niacin therapy for cholesterol is a separate, medically supervised use with its own risk profile.

Recommended intakes are typically expressed in niacin equivalents (NE), which account for the niacin your body makes from tryptophan.

• Adult men: around 16 mg NE per day
• Adult women: around 14 mg NE per day
• Pregnancy: around 18 mg NE per day
• Breastfeeding: around 17 mg NE per day

Most people eating a varied diet with some protein and grains meet these amounts without trying.

Niacin from food is considered very safe, with no known risk of toxicity at normal dietary levels.

Supplemental nicotinic acid at higher doses commonly causes a harmless but uncomfortable flushing reaction: skin redness, warmth, and tingling, especially in the face and chest.

• Flushing and itching (most common, especially with nicotinic acid)
• Stomach upset or nausea
• Liver enzyme changes at high doses
• Elevated blood sugar with prolonged high-dose use
• Gout flares in susceptible people

Nicotinamide (niacinamide) does not typically cause flushing, which is why it is often used in skincare and lower-dose supplements instead of nicotinic acid.

There is a tolerable upper intake level set for supplemental niacin, generally around 35 mg per day for adults, specifically because of the flushing reaction. This limit does not apply to niacin naturally occurring in food.

• People with very restrictive diets low in protein and whole grains
• People with alcohol use disorder, which can impair absorption and increase needs
• People with malabsorption conditions affecting nutrient uptake
• People in regions where corn is a dominant, unfortified dietary staple
• Anyone considering high-dose niacin supplements for cholesterol, who should understand the modern evidence and discuss it with a clinician rather than self-dosing

Niacin is a foundational B vitamin that your cells need to make energy, and most people get plenty from meat, fish, grains, and fortified foods.

Deficiency is rare today but historically serious. High-dose niacin supplements are a different matter entirely, with real side effects and a mixed track record for heart disease prevention, so they deserve caution rather than casual use.