Vitamin B3 (Niacin)

Niacin, also called vitamin B3, is a water-soluble B vitamin. The word covers two main forms, nicotinic acid and nicotinamide (also called niacinamide). It also covers related compounds such as nicotinamide riboside, says the NIH (the US National Institutes of Health).

The body turns them into NAD, a helper molecule that more than 400 enzymes need. They use it to move energy out of carbohydrates, fats and proteins and to keep the genome (your DNA) intact. Riboflavin and vitamin B6 help the body make niacin from tryptophan.

Niacin is not strictly a vitamin, the EU’s Scientific Committee on Food points out. The body can make it from the essential amino acid tryptophan. By convention, 60 mg of tryptophan count as 1 mg of niacin, so intakes are measured in niacin equivalents (NE).

The disease of too little niacin, pellagra, was once a mass problem. The committee reports more than 170,000 cases a year in the southern United States between 1910 and 1935.

What most readers do not know is how differently the two forms behave. Nicotinic acid in doses of 30 to 50 mg or more turns the skin red and itchy. Doses more than 100 times the daily allowance lower LDL (“bad”) cholesterol and triglycerides and raise HDL (“good”) cholesterol. Yet two trials of about 29,000 people found no fewer heart attacks.

Nicotinamide does not flush and lacks the cholesterol effect of nicotinic acid. But it cut new skin cancers by 23% in one trial of 386 people. The studies below weigh both forms, the newer NAD precursors and the food sources.

Health benefits of niacin

• ★★★No fewer heart attacks, strokes or deathsNiacin pills did not reduce deaths, heart attacks or strokes across 23 trials, and most people also took a statin. In another trial of 3,414 people with heart disease, extended-release niacin on top of a statin did not lower heart attacks or strokes either.
• ★★★More new diabetes diagnosesIn 11 trials of people without diabetes, niacin given as a treatment raised new diabetes diagnoses by 34% (1.34 times the risk). That is one extra case for every 43 people treated for 5 years.
• ★★Nicotinamide: fewer skin cancers in one trial onlyNicotinamide, one form of vitamin B3 (not food niacin), cut new nonmelanoma skin cancers by 23% in a year in high-risk adults. It did not lower new skin cancers in organ-transplant recipients.
• ★★Serious side effects with niacin plus laropiprantA tablet combining niacin with laropiprant, which blunts flushing, did not cut major vascular events (13.2% against 13.7% on placebo) in 25,673 adults on statins. Serious diabetes-control problems rose by 3.7 percentage points.
• ★★No-flush niacin did not improve blood fatsIn 120 adults with mild dyslipidemia (slightly abnormal blood fats), extended-release niacin lowered total cholesterol 11% in 6 weeks. “No-flush” inositol hexanicotinate and placebo showed no clear improvement.

Foods high in niacin

Seafood and poultry lead our USDA ranking per serving, against a Daily Value of 16 mg (the FDA’s daily target for food labels). Tuna gives 13.1 mg in 3 oz (85 g) and chicken breast 10.8 mg in 4 oz (113 g). Mackerel gives 10.2 mg per fillet (112 g). Farmed Atlantic salmon, ground lamb and other fish and meats follow, and peanuts end the list, as the ranking shows.

Per 100 g, tuna (15.4 mg) and peanuts (12.1 mg) lead, followed by chicken breast (9.6 mg), hemp seeds, mackerel and chia seeds. Per 100 kcal, white mushrooms come first (16.4 mg), then tuna (15 mg) and chicken breast (8 mg).

The NIH table adds beef liver at 14.9 mg in 3 oz and roasted turkey breast at 10.0 mg. Sockeye salmon and canned light tuna in water have 8.6 mg each, pork tenderloin 6.3 mg and cooked brown rice 5.2 mg per cup. A breakfast cereal fortified with 25% of the Daily Value has 4.0 mg. That is why tuna values differ between tables: they depend on the kind of tuna and how it is prepared.

The NIH notes that animal foods give about 5 to 10 mg per serving, mainly as NAD and NADP, which are highly bioavailable (well absorbed). Nuts, legumes and grains give about 2 to 5 mg, mainly as nicotinic acid.

Tables list niacin only, not the extra from tryptophan. A 3 oz portion of turkey breast holds about 180 mg of tryptophan, which could be equivalent to 3 mg of niacin.

Form matters as much as amount. In some grain products the natural niacin is bound to sugars and peptides and is only about 30% bioavailable, the NIH says. The Scientific Committee on Food calls the bound niacin of cereals essentially not absorbed.

A 2025 review reports that the traditional Mesoamerican soaking of maize in lime water releases bound niacin. That helps explain why corn eaten without that step has been linked to pellagra. Niacin added to enriched and fortified foods is free and highly bioavailable.

Roasted coffee contains free nicotinic acid: 160 to 400 mg per kg of roasted coffee in one measurement the committee cites. We found no study of niacin losses in home cooking that we could verify, so we give no loss figure. The committee notes that boiling sweet corn releases most of its niacin as nicotinamide.

How niacin works

Most of the biochemistry below is well established. But the details of the receptors come from cells and mice, and the human findings come from metabolic studies more than from trials.

Five ideas cover it. Three routes lead to NAD, and tryptophan counts at about 60 to 1. Nicotinic acid acts on a receptor in fat cells, and the same kind of receptor in skin causes the flush.

The end products of excess niacin may matter. After them comes what has been seen in people.

Three routes lead to NAD

Inside cells, niacin matters because it becomes NAD (nicotinamide adenine dinucleotide). More than 400 enzymes need NAD, according to the NIH. They use it to move the energy in food into ATP, to maintain genome integrity and to control gene expression.

NADP, which all tissues except skeletal muscle make from NAD, drives building reactions such as making cholesterol and fatty acids. It also keeps antioxidant defenses working.

The Scientific Committee on Food describes how nicotinic acid reaches NAD in a few steps, by way of nicotinic acid mononucleotide. Nicotinamide is converted more directly. The NAD and NADP in animal foods are broken down to nicotinamide in the gut before absorption. The liver also builds NAD from tryptophan.

Nicotinamide riboside and nicotinamide mononucleotide (NMN) are further NAD precursors. In a first trial of nicotinamide riboside in people, single doses of 100, 300 and 1,000 mg produced dose-dependent rises in blood NAD+ compounds.

Tryptophan counts, at about 60 to 1

The body converts some of the tryptophan in protein to niacin, so protein foods count twice. The usual rule is 60 mg of tryptophan for 1 mg of niacin, which both the NIH and EFSA use. How well the conversion works differs between people.

In a study, 10 young Japanese women ate a niacin-free purified diet for 7 days. The authors calculated that 67 mg of tryptophan would equal 1 mg of niacin if the urine carried 60% of the niacin made. The NIH adds that the enzymes involved need riboflavin, vitamin B6 and iron, so people short of them convert less.

Nicotinic acid switches down fat release

At gram doses, nicotinic acid changes blood fats through a receptor. In 2003, researchers showed that a receptor named PUMA-G in mice, HM74 in humans, is highly expressed in fat tissue and binds nicotinic acid. Binding lowers the cell’s cAMP (a signal molecule), which slows the breakdown of stored fat.

In mice without the receptor, nicotinic acid no longer lowered free fatty acids or triglycerides in the blood. Nicotinamide does not bind the receptors behind these effects, the NIH says, which is why it does not change blood fats.

The flush starts in the skin

The same kind of receptor, GPR109A, sits on skin cells. In mice, the early phase of the flush depends on it in Langerhans cells and a COX-1 enzyme. The late phase depends on it in keratinocytes and a COX-2 enzyme, with prostaglandins (local signal molecules) as the signal. Langerhans-like cells grown from human blood cells also released prostaglandin D2 when given nicotinic acid.

The prostaglandins widen small blood vessels. That fits with aspirin, which blocks prostaglandin formation, easing flushing in a trial of 277 adults. It also fits with the niacin tablet in HPS2-THRIVE being paired with laropiprant, a drug that blocks the prostaglandin D2 receptor.

The end products of excess niacin may matter

When intake is high, the liver methylates the surplus (adds a methyl group). This makes products such as N1-methyl-2-pyridone-5-carboxamide (2PY). A related compound, 4PY, also forms, and both leave in the urine, according to the NIH.

In two cohorts of heart patients, high blood 2PY and 4PY went with a higher 3-year risk of major cardiovascular events. In mice, 4PY raised an adhesion molecule on blood vessel walls. The study did not test whether eating less niacin would change that risk.

What has been seen in people

The mechanisms fit the pattern in the trials but not the hoped-for outcomes. The blood-fat changes are real. In AIM-HIGH, HDL cholesterol rose from 35 to 42 mg/dL and triglycerides fell from 164 to 122 mg/dL. Yet the main outcome occurred in 16.4% of the niacin group and 16.2% of the placebo group.

The flush is real too, and aspirin cut the share with moderate or worse flushing from 29% to 15%. NAD precursors raise blood NAD in people. But 12 weeks of nicotinamide riboside did not improve insulin sensitivity in 40 obese men. A year of it left 410 people with early Parkinson disease slightly worse than placebo.

The clearest human story is still deficiency. In Malawi, 6.3% of refugees developed pellagra after groundnut rations stopped, and daily isoniazid raised the odds of pellagra 42.6-fold. All of these are among the study cards above and below.

How much niacin do you need?

Women need 14 mg and men 16 mg of niacin equivalents (NE) a day from age 19 on. That is the US recommended dietary allowance (RDA), an amount that covers nearly all healthy people. One NE is 1 mg of niacin or 60 mg of tryptophan.

EFSA sets the EU population reference intake per unit of energy instead of per day. That is 1.6 mg NE per megajoule, or 6.6 mg NE per 1,000 kcal. For a 2,000 kcal diet, it comes to about 13 mg NE. Its average requirement is 1.3 mg NE per megajoule.

Pregnancy raises the US allowance to 18 mg NE a day and breastfeeding to 17 mg NE. For children it is 6 mg NE at ages 1 to 3, 8 mg at 4 to 8 and 12 mg at 9 to 13. From 14 to 18 it is 14 mg for girls and 16 mg for boys. There is no separate value for older adults.

EFSA found no evidence that the link between niacin and energy needs differs in infants aged 7 to 11 months, children, teenagers, pregnancy or breastfeeding. So it applies the same 1.6 mg NE per megajoule to all of them.

Most people in the US already meet these values. Men average 31.4 mg of niacin a day from food and drink, and women 21.3 mg. Only 1% of adults fall below the average requirement, the NIH reports.

The body makes niacin from tryptophan. So the Scientific Committee on Food concluded that a normal diet with enough tryptophan may need no preformed niacin at all.

Niacin deficiency: signs and who is at risk

Severe deficiency causes pellagra. The NIH describes a pigmented, rough, sunburn-like rash on skin exposed to sunlight, a bright red tongue, vomiting, and constipation or diarrhea. Nervous system signs include depression, apathy, headache, fatigue, memory loss that can progress to aggressive or paranoid behavior, and hallucinations. Untreated, pellagra ends in death.

It is uncommon in industrialized countries and mostly affects people living in poverty on very limited diets, such as refugees. In Malawi in 1990, 18,276 of 285,942 Mozambican refugees developed pellagra after groundnut rations stopped. In postwar Angola, low urinary niacin metabolites were found in 29.4% of 723 women and 6.0% of 690 children. The authors say the disease is endemic there.

The NIH lists the groups most at risk. These include people with undernutrition, such as those with anorexia, alcohol use disorder, AIDS, inflammatory bowel disease or liver cirrhosis. People who get too little riboflavin, vitamin B6 or iron are also at risk, because the conversion of tryptophan needs them.

So are people with Hartnup disease, a rare inherited disorder that interferes with tryptophan absorption. People with carcinoid syndrome are too, because their tryptophan is diverted to serotonin.

People taking isoniazid or pyrazinamide for tuberculosis are at risk as well. In a Malawi case-control study, the odds of pellagra were 42.6 times higher with daily isoniazid. The risk was higher in the season of food scarcity.

Blood levels of niacin are not a reliable measure of status. The NIH says the best measure is the urinary excretion of two methylated metabolites. Above 17.5 micromol a day reflects adequate status, 5.8 to 17.5 low status, and below 5.8 deficiency.

Diagnosis rests mainly on the signs, and treatment should not wait for a test. The World Health Organization recommends 300 mg a day of nicotinamide in divided doses for 3 to 4 weeks, with a B-complex or yeast product. That is because other B vitamin deficiencies often come with it.

Forms of niacin: absorption and effects

“Niacin” on a label can mean several different compounds. Nicotinic acid is the form that flushes and, at gram doses, changes blood fats. Nicotinamide (niacinamide) does not flush and lacks that effect on blood fats. It is the usual form in multivitamins and in the skin cancer trials.

Inositol hexanicotinate is six nicotinic acid units on one inositol molecule, sold as “flush-free”. The words “extended-release”, “sustained-release” and “timed-release” describe how a nicotinic acid tablet dissolves, not a different compound.

Nicotinamide riboside and nicotinamide mononucleotide are NAD precursors. The NIH says they are not marketed or labeled as sources of niacin in the US, although the EU assessed both as sources of niacin.

The honest bottom line: the forms were compared head to head only for blood fats, flushing and liver safety. Nearly all supplement doses in the outcome trials were drug doses.

We found no trial that compared nicotinamide riboside or NMN with nicotinamide or nicotinic acid for any health outcome. So the idea that NAD precursors work better than plain niacin rests on blood NAD levels. The popular claim that “no-flush” niacin lowers cholesterol has a trial behind it, and the trial says it does not.

The forms in the outcome trials above were as follows. The Coronary Drug Project and ADMIT used nicotinic acid. AIM-HIGH used extended-release nicotinic acid, and HPS2-THRIVE used it with laropiprant. ONTRAC and ONTRANS used nicotinamide (500 mg twice a day), and ENDIT used modified-release nicotinamide.

The Parkinson, obesity, artery disease and older-adult trials used nicotinamide riboside. The prediabetes trial used NMN.

Form	Activity or conversion	What studies show	Source
Nicotinic acid, immediate-release	1 mg niacin = 1 mg NE; flushing from about 30 to 50 mg	Almost completely absorbed even at 3 to 4 g a day, according to the NIH. At gram doses it raises HDL cholesterol 10% to 30% and lowers LDL cholesterol 10% to 25% and triglycerides 20% to 50%. None of 23 adults on immediate-release niacin developed liver toxicity, but 39% withdrew before the 3,000 mg step, mainly for flushing and fatigue.	1, 3
Nicotinic acid, extended- or sustained-release	1 mg niacin = 1 mg NE; slower release	Sustained-release niacin damaged the liver in 52% of 23 adults, and the NIH says liver toxicity is more likely with extended-release forms. A wax-matrix extended-release form lowered LDL cholesterol 18% in 6 weeks. Extended-release niacin was the form in AIM-HIGH and, with laropiprant, in HPS2-THRIVE, and neither trial found fewer cardiovascular events. Prescription products give 500 to 1,000 mg.	1, 3, 4, 7, 8
Nicotinamide (niacinamide)	1 mg niacin = 1 mg NE; no flushing	Does not bind the receptors behind the lipid effects of nicotinic acid, so it lacks the cholesterol-lowering effect of nicotinic acid, and it is almost completely absorbed. It was the form in ONTRAC (23% fewer new skin cancers) and ENDIT (no effect on type 1 diabetes). In hemodialysis it lowered phosphorus but raised the risk of low platelets. The EU upper level is 900 mg a day, against 10 mg for nicotinic acid.	1, 2, 9, 10, 11
Inositol hexanicotinate (“no-flush”)	Not stated	The NIH says absorption varies widely and is on average 30% lower than from nicotinic acid or nicotinamide. In a trial of 120 adults it did no better than placebo for blood fats, and a small substudy found no evidence of bioavailability. Tested “no-flush” products contained no free nicotinic acid.	1, 4, 5
Nicotinamide riboside (NR)	Not stated	Raises blood NAD+ in people. It did not improve insulin sensitivity in 40 obese men, gave a small gain in walking distance in 90 people with artery disease, and left 410 people with early Parkinson disease slightly worse than placebo. EFSA judged the chloride safe at up to 300 mg a day for healthy adults, but in 2021 found its safety in meal replacements and drink mixes not established.	12, 13, 14, 15, 16, 19, 21
Nicotinamide mononucleotide (NMN)	Conversion factor of 1 against nicotinamide in equimolar amounts (EFSA)	Improved muscle insulin sensitivity in prediabetic women over 10 weeks. A 2026 meta-analysis of 15 trials (250 to 2,000 mg a day) found no increase in adverse events and no clear effect on weight, glucose, HbA1c, blood fats or systolic blood pressure. EFSA judged 300 mg a day safe for healthy adults, excluding pregnant and lactating women.	17, 18, 20

Here are the head-to-head and form-specific studies, strongest evidence first, six in all.

Is niacin safe? Supplements, dose and interactions

Niacin from food is not a safety concern: the NIH says no adverse effects have been reported from naturally occurring niacin in foods. The limits cover supplements and fortified foods.

The US tolerable upper intake level (UL), the highest daily amount unlikely to cause harm, is 35 mg a day for adults. It is 30 mg for ages 14 to 18 and 20 mg for 9 to 13. It is 15 mg for 4 to 8 and 10 mg for 1 to 3. The 30 and 35 mg values also apply in pregnancy and breastfeeding, and none is set for infants.

The UL rests on skin flushing. The NIH says it applies to both supplemental forms, because a flush-based limit can also prevent the possible effects of excess nicotinamide. It does not apply to people taking niacin under medical supervision. In 2003 to 2006 survey data, 10% of supplement users reached or exceeded it.

The EU handles the two forms separately. In 2002, the Scientific Committee on Food set an upper level of 10 mg a day of free nicotinic acid for adults. It was based on occasional flushing at 30 mg and a safety factor of 3. For nicotinamide, which does not flush, it set 900 mg a day (12.5 mg per kg of body weight).

Neither value was set for pregnancy or breastfeeding for lack of data. The committee noted that flushing has not been reported for the bound forms of nicotinic acid in food. EFSA’s 2021 opinion on nicotinamide riboside repeats the 900 mg figure and says a re-evaluation of the nicotinamide level may be warranted.

• Flushing. The NIH says 30 to 50 mg or more of nicotinic acid typically causes reddening of the face, arms and chest, often within 30 minutes. It comes with burning, tingling or itching, and can come with headache, rash, dizziness or a drop in blood pressure. Taking it with food, raising the dose slowly or waiting for tolerance can help. In a trial of 277 adults, aspirin cut moderate or worse flushing from 29% to 15%.
• Liver, blood sugar and other effects of gram doses. At 1,000 to 3,000 mg a day, the NIH lists low blood pressure, impaired glucose tolerance, stomach upset and blurred vision. It also lists macular edema (swelling in the retina) and liver toxicity, more likely with extended-release forms. Sustained-release niacin damaged the liver in 52% of 23 adults. In a meta-analysis, niacin raised the risk of new diabetes by 34%. In HPS2-THRIVE, it raised serious muscle, skin, stomach and bleeding events. The ACC and AHA (US heart medicine bodies) advise checking liver enzymes, blood sugar and uric acid before and during high-dose use.
• Nicotinamide. Nausea, vomiting and signs of liver toxicity can occur at 3,000 mg a day, the NIH says. A review of its safety advises against unsupervised use above 3 g a day. In hemodialysis patients it lowered phosphorus, with an increased risk of low platelets in a meta-analysis.
• Drug interactions. Isoniazid and pyrazinamide, used against tuberculosis, interrupt the body’s own niacin production. Daily isoniazid was linked to pellagra in Malawi, so extra niacin can be needed. Large doses of nicotinic acid can raise blood sugar, particularly at 1.5 g a day or more. People on antidiabetes medicines may need dose changes. Because high doses can lower blood pressure, people on blood pressure medicines should ask first.
• Who should ask a doctor. Ask before taking niacin above the upper level, and ask if you have liver disease, diabetes, gout or unexplained stomach pain. Ask too if you take a statin or other cholesterol medicine, or isoniazid. The ACC and AHA advise stopping high-dose niacin for persistent high blood sugar, acute gout, new atrial fibrillation or severe skin reactions. Doses in the thousands of milligrams are a drug treatment and should only be taken with medical supervision.

How to get more niacin

• Best foods. In our ranking tuna gives 13.1 mg in 3 oz, chicken breast 10.8 mg in 4 oz and peanuts 3.42 mg in 1 oz. The NIH adds beef liver at 14.9 mg and turkey breast at 10.0 mg in 3 oz.
• Let protein do double duty. Tryptophan in protein can be converted to niacin at about 60 to 1. So a 3 oz portion of turkey breast adds roughly 3 mg of niacin equivalents beyond the 10.0 mg in the tables.
• Choose the form of grain. The niacin in unprocessed maize and some other grains is largely bound. Lime-treated maize and enriched or fortified grain products give niacin in a form the body can use. Most US adults need no supplement: only 1% of adults fall below the average requirement.

History of niacin

Pellagra was unknown in Europe before maize arrived from the New World. In the 18th century, Casàl and Frapolli described its signs in Europe and tied it to poverty and diets of little but corn. The Scientific Committee on Food dates its recognition to 1735.

It hit Italy, southern France and Spain, and later the southern United States. There, the committee reports more than 170,000 cases a year between 1910 and 1935.

From 1914 to 1929, Joseph Goldberger ran epidemiological investigations, tested theories in human experiments and used “black tongue” in dogs as an animal model. All of it supported a dietary cause over the poison and infection theories of the day, a historical review reports.

Dried brewer’s yeast could cure or prevent pellagra more cheaply than changing diets, but poverty limited its use. In 1937, Conrad Elvehjem’s group isolated the pellagra-preventive factor and identified it as nicotinic acid. They showed that nicotinic acid and its amide cure black tongue in dogs.

Fortification of foods with vitamins during the Second World War ultimately ended endemic pellagra in the United States. In the 1940s and 1950s, pellagra was reframed as a deficiency of niacin and its precursor tryptophan.

The cholesterol story came next. The NIH dates studies of nicotinic acid in blood fats to the late 1950s, and the Coronary Drug Project ran from 1966 to 1975. AIM-HIGH in 2011 and HPS2-THRIVE in 2014 ended the hope that it adds to statins. The 2015 ONTRAC trial opened a new line of work with nicotinamide and skin cancer.

Frequently asked questions about niacin

Why does niacin make your skin flush?

Nicotinic acid triggers it. The NIH says 30 to 50 mg or more typically reddens the face, arms and chest with burning or itching, often within 30 minutes. In mice, nicotinic acid activates a receptor on skin cells that release prostaglandins, which widen small blood vessels. Aspirin cut moderate or worse flushing from 29% to 15% in a trial of 277 adults. Nicotinamide does not cause flushing. The committee that set the EU limits found no report of it from the bound niacin in food.

Is niacin the same as niacinamide?

Both are vitamin B3, and the body makes NAD from either, but they act differently. Niacinamide is another name for nicotinamide. It does not flush and lacks the cholesterol-lowering effect, while nicotinic acid has both. The upper levels differ too. The US limit for supplemental niacin is 35 mg a day. In the EU it is 10 mg for nicotinic acid against 900 mg for nicotinamide.

Does niacin lower cholesterol, and does that prevent heart attacks?

Gram doses of nicotinic acid raise HDL cholesterol and lower LDL cholesterol and triglycerides, but the extra benefit for the heart was not found. AIM-HIGH (3,414 people) found 1.02 times the risk, and HPS2-THRIVE (25,673 people) 0.96 times. A Cochrane review of 23 trials found no fewer deaths, heart attacks or strokes. Those doses are 1,000 to 3,000 mg and are medical treatment, not a supplement to start alone.

How much niacin should I take a day?

Women need 14 mg and men 16 mg of niacin equivalents a day, with 18 mg in pregnancy and 17 mg while breastfeeding. EFSA’s EU value is 1.6 mg NE per megajoule, about 13 mg for 2,000 kcal. Most US adults already get more from food: 31.4 mg for men and 21.3 mg for women on average. A supplement above 35 mg a day goes past the US upper level.

Which foods are highest in niacin?

Tuna leads our USDA ranking per serving with 13.1 mg in 3 oz. Chicken breast (10.8 mg in 4 oz), mackerel (10.2 mg per fillet) and farmed Atlantic salmon (7.37 mg in 3 oz) follow. Per 100 g, peanuts (12.1 mg) and hemp seeds (9.2 mg) join them. The NIH lists beef liver at 14.9 mg in 3 oz, and enriched grain products add niacin in a form the body absorbs well.

Can you take too much niacin?

Yes, from supplements, but not from food. Above about 30 to 50 mg, nicotinic acid brings the flush. At 1,000 to 3,000 mg a day, the NIH lists liver toxicity, high blood sugar and low blood pressure. Sustained-release niacin damaged the liver in 52% of 23 adults, and niacin raised the risk of new diabetes by 34% in a meta-analysis. Nicotinamide is gentler, with nausea and liver signs at around 3,000 mg a day.

Does niacinamide prevent skin cancer?

In one trial, it lowered new nonmelanoma skin cancers by 23% in 386 high-risk adults who took 500 mg twice a day for a year. The benefit faded after stopping. It had no effect in 158 transplant recipients, and a meta-analysis of four trials called the evidence insufficient. This is a medical dose and a decision for a dermatologist, not a reason to take niacin at food amounts.

Do NAD precursors like nicotinamide riboside and NMN work?

They raise NAD in the blood, but no health benefit is established. Nicotinamide riboside did not improve insulin sensitivity in 40 obese men. In 410 people with early Parkinson disease, it left scores slightly worse than placebo. NMN improved muscle insulin sensitivity in prediabetic women over 10 weeks in one trial. EFSA judged up to 300 mg a day of either safe for healthy adults, with pregnant and lactating women excluded from that conclusion.