What are the signs of niacin (B3) deficiency?

Severe niacin deficiency causes pellagra, whose first visible sign is a pigmented rash on skin exposed to sunlight.

Who is most likely to run low

Undernourished people, including those with alcohol use disorder, AIDS, inflammatory bowel disease or liver cirrhosis, often take in too little niacin.

What this means for you

Severe niacin deficiency has a name, pellagra, and a textbook line repeated for a century: dermatitis, diarrhoea and dementia, with death if it goes untreated. The modern case record half agrees.

The first visible sign is a rash on skin that gets sunlight, which darkens and takes on a roughened, sunburned look. That pattern, appearing symmetrically on the hands, neck or face, is what separates it from ordinary skin complaints.

Unsettled. Across 1,212 confirmed cases published between 2000 and 2023, skin changes turned up in 98.63 per cent. The gut signs came in 59.4 per cent and the nerve signs in 54.2 per cent, so the other two thirds of the famous trio are present in a little over half of patients. The rash is the sign that can be relied on. The rest may or may not be there.

Why that number needs a warning label

The review behind it screened 918 studies, and every one it could use was a case report or a small series of patients. Nobody has run a trial on pellagra. Nobody is likely to, because the trial worth running would have to leave one group of sick people without vitamin B3. What we have instead is a pile of individual stories, written up by the doctors who found them worth writing up.

That bends the numbers in a direction you can predict. A patient with a striking rash gets published. A patient who is confused and losing weight without one often does not. So read 98.63 per cent as a statement about what reaches journals rather than as the odds facing any one person.

For a reader this has one sharp edge. Do not treat the three Ds as a checklist that rules pellagra out. If someone who has been eating badly for months has the rash, that alone is worth a doctor, and waiting for the other two signs to arrive is how the diagnosis gets missed.

Who it happens to now

Established. Not having enough food is still the cause in 85 per cent of cases, and 93 per cent of those arose where food insecurity or a humanitarian crisis had made ordinary eating impossible. Alcohol misuse accounted for 9.6 per cent. The tuberculosis drug isoniazid was behind 14.3 per cent, the largest drug-related share.

The isoniazid figure carries the same caution as the rest. A case caused by a drug makes a more interesting write-up than a case caused by poverty, so its share of the published cases is probably bigger than its share of the real ones. It is still worth knowing if you take isoniazid, and it is a question for the clinician running that treatment.

Not for everyone. Most people this happens to are undernourished for a reason: poverty, anorexia, alcohol use disorder, AIDS, inflammatory bowel disease or liver cirrhosis. In each of those, niacin is one shortage among several, and the treatment belongs to a clinician rather than to a supplement shelf.

If treatment has started, give it weeks

In the published cases, complete resolution came on average 27.42 days after vitamin B3 was started. A week of tablets with the rash still in place is no sign the diagnosis was wrong.

An ordinary diet keeps all of this away without anyone thinking about it. Meat, fish, poultry, nuts and fortified grains carry niacin, and the body makes more of it from tryptophan in protein. If you are short of riboflavin, vitamin B6 or iron, that conversion works less well, which is why a niacin problem is sometimes a different problem wearing a niacin mask.

One clarification, because searching for niacin brings back mostly heart medicine. The doses used there are forty times what food carries, and they were tested properly and failed. A meta-analysis of 35,760 patients with heart disease or high cholesterol found no protective effect on cardiovascular outcomes. Nothing about that changes the vitamin story, and a pellagra rash is not treated by a cholesterol dose bought over the counter.

How long it takes, and why that matters

The body keeps almost no reserve of niacin. On a corn-based, niacin-poor diet, deficiency symptoms appear after about 50 to 60 days. Two months from a diet going wrong to a visible illness, which is fast enough to follow a crisis and slow enough that nobody connects the two.

That timing also explains the geography of pellagra. Maize is low in available niacin, and the one preparation known to release it is alkaline treatment, the lime-soaking that makes tortillas. Where maize travelled without that step, pellagra followed it. Where it was always prepared that way, the disease stayed rare.

Not for everyone. A niacin shortage is not always a niacin shortage. The body makes niacin from tryptophan at about 60 to 1, and that conversion falls when tryptophan itself is short, in the inherited condition Hartnup disease, and when iron, riboflavin or vitamin B6 are missing. So low niacin can be the visible end of a different deficiency, or of eating too little overall. Treating it with niacin alone would leave the real problem where it was. This is a reason the diagnosis belongs to a clinician rather than to a symptom list.

Written from the evidence cards and the data on this page, then checked back against the sources. Bioma Learn has no human medical reviewer at this time and we say so rather than invent one. Information, not medical advice. How we verify.

Where to get it from food

• Acai berry drink, fortified fortified — 24.1 mg per 8 fl oz (151% DV)
• Chicken, breast, cooked, roasted — 19.2 mg per 1 cup, chopped or diced (120% DV)
• Chicken, light meat, cooked, roasted — 17.4 mg per 1 cup, chopped or diced (109% DV)
• Chicken, meatless, breaded, fried fortified — 16.6 mg per 1 cup, diced (104% DV)
• Chicken, broiler or fryers, breast, skinless, cooked — 16.4 mg per 1.0 piece (103% DV)

All niacin (B3) sources ranked →

Full guide: Niacin: the vitamin that became a heart drug and then failed the trials