Niacin is a B vitamin your body uses to turn food into energy and repair DNA

Niacin, also called vitamin B3, works in nearly every cell to convert carbohydrates, fats, and proteins into usable energy. It also helps your body repair damaged DNA and supports the function of your nervous system and digestive tract. Unlike some vitamins your body can store, niacin is water-soluble, meaning excess amounts leave your body through urine—so you need a steady supply from food or supplements.

Your body can make a small amount of niacin from the amino acid tryptophan, but most people get what they need from eating meat, fish, poultry, nuts, seeds, and whole grains. A deficiency is rare in developed countries but can happen with severe malnutrition or certain medical conditions. The recommended daily amount is 14 to 16 mg for most adults, depending on age and sex.

Key Takeaways

  • Niacin helps convert food into energy and is essential for DNA repair and nervous system function.
  • Most people meet their niacin needs through everyday foods like chicken, tuna, peanuts, and brown rice.
  • Niacin supplements in high doses can cause flushing, itching, and stomach upset, and may interact with medications.
  • A severe niacin deficiency causes pellagra, a condition marked by skin problems, digestive issues, and mental changes—now uncommon but still seen in cases of extreme malnutrition.

How niacin works in your body

Niacin exists in two main forms: nicotinic acid and nicotinamide. Both convert to NAD (nicotinamide adenine dinucleotide), a coenzyme that acts like a shuttle, moving electrons during energy production in your cells. Without enough NAD, your cells cannot efficiently extract energy from the food you eat, leaving you fatigued and unable to function normally.

Beyond energy, niacin supports your skin barrier, helps regulate cholesterol and blood sugar, and protects nerve cells from damage. It also plays a role in reducing inflammation and supporting mental health, though research on these effects is still developing. Your liver, kidneys, and brain all depend on steady niacin levels to work properly.

Food sources of niacin

Animal proteins are the richest sources: a 3-ounce serving of chicken breast contains about 8 mg, tuna has 5 to 6 mg, and turkey has 4 to 5 mg. Beef, pork, and salmon also provide significant amounts. If you eat meat regularly, you are likely meeting your niacin needs without thinking about it.

Plant-based sources include peanuts and peanut butter (about 4 mg per ounce), sunflower seeds, almonds, mushrooms, asparagus, and whole grains like brown rice and oats. Fortified cereals and breads often have added niacin. If you follow a vegetarian or vegan diet, combining legumes with whole grains—such as beans and rice—helps you reach your daily target, though you may need to eat larger portions or include fortified foods.

When niacin supplements make sense

Most people do not need niacin supplements if they eat a varied diet with protein sources. Supplements are sometimes recommended for people with restricted diets, certain digestive disorders that affect nutrient absorption, or specific medical conditions. Some people take niacin under medical supervision for cholesterol management, though this use requires a doctor's oversight because high doses carry risks.

If you are considering a niacin supplement, start with a B-complex vitamin that includes niacin at the recommended daily amount rather than a high-dose product. This approach covers your baseline needs without the side effects of megadosing. Always tell your doctor about any supplements you take, especially if you are on medications for cholesterol, blood pressure, or diabetes.

Side effects and risks of high-dose niacin

Niacin flushing is the most common side effect of supplements, especially doses above 50 mg. Your skin turns red and warm, and you may feel itching or tingling, usually lasting 15 to 30 minutes. This is harmless but uncomfortable. Taking niacin with food or choosing the form called inositol hexanicotinate (which causes less flushing) can reduce this reaction.

Higher doses can cause nausea, stomach upset, and liver problems with long-term use. Niacin can also raise blood sugar levels and interact with medications for gout, blood pressure, and cholesterol. Pregnant women should not take high-dose niacin supplements without medical guidance. If you have liver disease, gout, or diabetes, talk to your doctor before taking niacin supplements beyond what is in a standard multivitamin.

Niacin deficiency and pellagra

Severe niacin deficiency causes pellagra, a condition marked by the "four Ds": dermatitis (skin problems), diarrhea, dementia, and death if untreated. Pellagra was common in the early 1900s in populations eating mainly corn without adequate protein, but it became rare after flour and grain fortification began. Today it appears mainly in people with severe malnutrition, untreated alcoholism, or certain medical conditions that prevent nutrient absorption.

Symptoms of pellagra include a distinctive rash on sun-exposed skin, chronic diarrhea, mouth sores, anxiety, depression, and confusion. If you suspect severe deficiency—which is unlikely unless you have a serious underlying condition—see a doctor for testing. Niacin supplements or dietary changes reverse early deficiency quickly, but advanced pellagra requires medical treatment.

Niacin and cholesterol: what the research shows

High-dose niacin (1,500 to 3,000 mg daily) has been studied for raising HDL cholesterol and lowering triglycerides, sometimes as part of a prescription medication. However, recent large trials have not shown that niacin reduces heart attack or stroke risk when added to statin therapy, and side effects limit its use. Niacin for cholesterol management is now less common than it was 10 years ago, and most doctors recommend statins or other medications first.

If your doctor suggests niacin for cholesterol, they will prescribe a specific dose and monitor your liver function and blood sugar regularly. This is different from taking a standard niacin supplement for general health. Do not self-treat high cholesterol with over-the-counter niacin supplements—work with your doctor to choose the right approach for your situation.

Frequently Asked Questions

Can niacin supplements give you energy if you are not deficient?

No. If you already have adequate niacin from food, taking more will not boost your energy or mental performance. Your body excretes excess niacin in urine. Energy comes from eating enough calories overall and getting enough sleep and exercise, not from megadosing a single vitamin.

Is niacin the same as niacinamide?

Both are forms of vitamin B3 and both convert to NAD in your body, but they have different effects on flushing and cholesterol. Niacinamide causes less flushing and is gentler on the stomach. Nicotinic acid (niacin) is more likely to cause flushing but has been studied more for cholesterol effects. For basic nutritional needs, either form works.

What happens if you take too much niacin?

Doses above 50 mg often cause flushing, itching, and nausea. Long-term high doses (over 1,500 mg daily) can damage your liver, raise blood sugar, and interact with medications. There is no benefit to megadosing if you are not deficient. Stick to the recommended daily amount unless a doctor prescribes a higher dose for a specific medical reason.

Do vegans need niacin supplements?

Not necessarily. Plant foods like peanuts, seeds, mushrooms, and whole grains contain niacin, and your body also makes some from tryptophan in legumes and nuts. Eating a varied diet with these foods usually covers your needs. If you eat mostly refined grains or have absorption issues, a B-complex supplement with niacin is a reasonable choice.