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Supplements

Niacin (vitamin B3): nicotinic acid, nicotinamide, flushing and pellagra

Niacin comes as nicotinic acid and nicotinamide, and the two behave differently in the body. Everyday needs are met by meat, fish, eggs and flour. Higher doses were once used to lower cholesterol, but flushing and liver effects limit them, so supplement strength matters.

Last checked: 2026-10-03

Key facts

At a glance.

  • Daily need

    The NHS gives 16.5mg for men and 13.2mg for women a day, from meat, fish, wheat flour and eggs.

  • Two forms, two limits

    The NHS says 17mg or less a day of nicotinic acid, or 500mg or less a day of nicotinamide, is unlikely to cause harm.

  • Flushing

    High doses of nicotinic acid can cause skin flushes, a warm red tingling of the face and upper body. Nicotinamide causes fewer such effects, per MedlinePlus.

  • Liver

    The NHS warns that taking high doses for a long time could lead to liver damage.

  • Pellagra

    The deficiency disease causes digestive problems, inflamed skin and poor mental function.

Two forms with different effects

Niacin is the collective name for nicotinic acid (also called nicotinate) and nicotinamide (niacinamide). The body makes the vital coenzymes NAD and NADP from either, and these drive energy release and many repair reactions. The NHS summarises niacin as releasing energy from food and keeping skin and nerves healthy.

The difference matters because only nicotinic acid triggers the characteristic flush, and only nicotinic acid has been used in high doses for blood fats. Labels may say vitamin B3, niacin, nicotinic acid or nicotinamide, so it helps to read the small print.

Food sources and daily need

Meat, fish, eggs and wheat flour are the main UK sources according to the NHS. MedlinePlus lists milk, enriched grains, rice, legumes, peanuts and poultry. The body can also convert some tryptophan from protein into niacin, which is why diets rich in protein rarely run short.

Pellagra: when intake fails

Pellagra is the disease of prolonged niacin shortage. MedlinePlus describes it as digestive problems, inflamed skin and poor mental function, a pattern sometimes remembered as diarrhoea, dermatitis and dementia. The skin changes appear on sun-exposed areas.

It is uncommon in the UK but may occur with chronic alcohol dependence, severe restriction of diet, malabsorption, some eating disorders, and certain rare metabolic conditions. Where it is suspected, doctors give niacin, usually as nicotinamide, alongside nutritional rehabilitation, and look for the underlying cause.

Flushing and the cholesterol story

Therapeutic doses of nicotinic acid lowered LDL cholesterol and raised HDL in older studies. MedlinePlus notes that when used for cholesterol, niacin can cause flushing, a feeling of warmth, redness, itching or tingling of the face, neck, arms or upper chest. The flush is harmless but frequently leads people to stop the treatment.

Nowadays, statins and other proven medicines are used first for cholesterol in UK practice, and over-the-counter niacin should not be used as a substitute for prescribed treatment. Anyone considering high-dose niacin for lipids needs medical supervision, with liver tests and glucose monitoring.

Liver, glucose and ulcer risks

MedlinePlus states that high niacin intake can raise blood glucose, damage the liver, aggravate peptic ulcers and cause skin rashes. These effects are dose-related and are why the NHS sets a low limit for nicotinic acid supplements. People with diabetes, liver disease, gout or stomach ulcers should be especially cautious.

  • Stay within the NHS amounts unless a doctor advises otherwise.

  • Report yellow skin or eyes, dark urine, severe itching or persistent nausea while taking niacin.

  • Take any prescribed niacin as directed; do not swap between nicotinic acid and nicotinamide products.

Practical tips for supplements

Because the safe nicotinic acid amount is far lower than for nicotinamide, check which form your multivitamin or B-complex contains. Standard multivitamins typically stay within safe limits, but “flush” products and high-strength capsules do not.

Frequently asked

Questions people ask.

Quick, plain-English answers to the questions we hear most.

  • How much niacin do adults need?

    The NHS says 16.5mg a day for men and 13.2mg a day for women. This is normally met by food.

  • What is the safe limit for supplements?

    The NHS says 17mg or less a day of nicotinic acid, or 500mg or less a day of nicotinamide, is unlikely to cause harm.

  • Why does niacin make my face go red?

    Nicotinic acid widens small blood vessels in the skin. It is usually harmless and settles, but it can be uncomfortable.

  • Is nicotinamide safer than nicotinic acid?

    It causes fewer side effects such as flushing, according to MedlinePlus, and has a higher NHS supplement limit, though high doses still need a reason.

  • Can niacin lower my cholesterol?

    Nicotinic acid can in high doses, but side effects limit its use and it is not a first-line treatment. Do not self-prescribe.

  • What are the symptoms of pellagra?

    Digestive upset, inflamed skin and poor mental function. It is rare in the UK and usually occurs with severe dietary lack or alcohol dependence.

  • Can niacin affect blood sugar?

    MedlinePlus lists raised blood glucose among the effects of high intake, which matters for people with diabetes.

  • Does niacin help skin?

    Niacin deficiency does damage skin, but the NHS does not present supplements as a skin treatment for people who are not deficient.

Where this comes from

Sources and checking.

This guide is for information, not medical advice.

Your GP or consultant knows your history and can tell you which parts apply to you. If your symptoms are severe, rapidly worsening, or come with red-flag features, seek urgent medical care. Figures and availability change, so treat them as a guide and confirm with the provider.

Published 2026-10-03, next review 2027-10-03.

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