NAD+ Precursors Explained: NR, NMN, Niacin and Food Sources

NAD+ precursors are the raw materials your cells use to build NAD+, a coenzyme found in every cell. There are four main ones in food and supplements: nicotinic acid and nicotinamide (the two forms of niacin, or vitamin B3), nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN). Your body can also make NAD+ from tryptophan, an amino acid in protein foods. Most people already get enough niacin from what they eat.

If you've read about NAD+ and aging, you've probably seen NR and NMN everywhere. They're only part of the story. Your body has been making NAD+ from ordinary food for as long as humans have eaten, using a few different routes. This guide lays those routes out side by side, explains how niacin and nicotinamide differ (one makes you flush, one doesn't), and lists the foods that supply the most. If you want the human trial details on NR and NMN, we cover those in our NAD+ vs NMN vs NR guide.

Last reviewed: October 29, 2026.

Key Takeaways

• Cells build NAD+ three ways: from tryptophan (the de novo route), from nicotinic acid (the Preiss-Handler route) and by recycling nicotinamide (the salvage route). NR and NMN feed into salvage.
• "Niacin" on a label can mean nicotinic acid or nicotinamide. Nicotinic acid can cause skin flushing at 30 to 50 mg or more. Nicotinamide doesn't.
• The adult RDA for niacin is 16 mg a day for men and 14 mg for women. In U.S. survey data, only about 1% of adults get less than the average requirement from food.
• Meat, poultry and fish are the richest food sources. Cow's milk carries NR, and some vegetables and fruits contain small amounts of NMN.
• No precursor has been shown to slow aging in people. The adult upper limit for niacin from supplements and fortified foods is 35 mg a day.

What is an NAD+ precursor?

NAD+ (nicotinamide adenine dinucleotide) is a coenzyme that helps enzymes turn food into usable energy. It's also used up by other enzymes, including sirtuins and PARPs, which take NAD+ apart as they work. A review from the Buck Institute for Research on Aging describes NAD+ as central to energy metabolism and notes that tissue NAD+ levels gradually decline with age in rodents and in humans (Covarrubias et al., 2021). We explain the basics in What Is NAD+?

Because NAD+ is constantly being used and rebuilt, your cells need a steady supply of building blocks. Those building blocks are the precursors. You don't absorb much NAD+ itself from a meal. The NIH Office of Dietary Supplements (ODS) explains that when you eat NAD and NADP in food, they're broken down to nicotinamide in the gut and then absorbed (NIH ODS, Niacin).

The NAD+ precursors at a glance

Three routes your body uses to make NAD+

Researchers group NAD+ production into three pathways (Covarrubias et al., 2021):

• De novo, from tryptophan. Your body can build NAD+ from scratch using tryptophan, an amino acid in protein. It's a long chain of steps called the kynurenine pathway, and it happens mostly in the liver. The ODS says this conversion depends on iron, riboflavin (B2) and vitamin B6, so people low in those nutrients make less.
• Preiss-Handler, from nicotinic acid. This route turns dietary nicotinic acid into NAD+ in three enzyme steps. The tryptophan route joins it partway through.
• Salvage, from nicotinamide. When enzymes use NAD+, they release nicotinamide. The salvage route recycles it back into NAD+. The review notes that NAD+ is constantly made, used up and recycled, and salvage is how cells keep their supply steady. NR and NMN enter here: NR gets converted to NMN, and NMN is one step away from NAD+.

NR's route was a fairly recent find. In 2004, Dartmouth researchers identified the enzymes (NR kinases) that let yeast and human cells use NR, which showed there was a path to NAD+ that didn't need to pass through nicotinic acid. The same paper noted that NR is a nutrient found in milk (Bieganowski and Brenner, 2004).

Why do the routes matter? Because each precursor behaves a little differently in the body. A 2008 review in the Annual Review of Nutrition points out that baseline NAD+ needs can be met with dietary tryptophan or with less than 20 mg of niacin a day, and that the distinct, tissue-specific activities of each precursor explain why each one has its own effects and side effects (Bogan and Brenner, 2008).

Niacin vs nicotinamide: same vitamin, different behavior

"Niacin" is the umbrella name for vitamin B3. The ODS defines it as nicotinic acid, nicotinamide (also called niacinamide) and related compounds such as nicotinamide riboside. Both nicotinic acid and nicotinamide are almost completely absorbed. On a supplement label, though, the two act quite differently:

• Nicotinic acid can cause the "niacin flush." According to the ODS, 30 to 50 mg or more of nicotinic acid typically causes the skin on the face, arms and chest to turn red as small blood vessels widen. It often comes with burning, tingling or itching and can start within 30 minutes. The ODS describes it as unpleasant rather than toxic, and it usually passes.
• Nicotinamide doesn't flush. Its slightly different chemical structure means it doesn't trigger that response.
• "Flush-free" niacin is a third form. Products labeled flush free often use inositol hexanicotinate. The ODS notes that absorption from this form varies widely and averages about 30% lower than from nicotinic acid or nicotinamide.

The flush is the reason some niacin products are labeled extended release or timed release. If you see "niacin" on a label and want to know which form you're getting, the ingredient list in parentheses usually tells you, for example "as niacinamide." Our guide to reading a Supplement Facts label walks through where to look.

How much niacin do you need?

Niacin needs are measured in milligrams of niacin equivalents (NE). One NE equals 1 mg of niacin or 60 mg of tryptophan, which is how the tryptophan in your food gets counted. Here are the RDAs for adults from the ODS:

*The upper limit applies to niacin from supplements and fortified foods, not to niacin found naturally in food. Source: NIH ODS.

Most Americans clear the RDA easily. In national survey data cited by the ODS, average intake from food and drinks was 31.4 mg a day for men and 21.3 mg for women, and only about 1% of adults got less than the estimated average requirement. That's worth keeping in mind. The research interest in NAD+ and aging is about NAD+ levels inside specific tissues as we get older, which isn't the same thing as not getting enough B3.

Foods with NAD+ precursors

Every food on this list supplies niacin, tryptophan or both. The ODS says animal foods typically provide about 5 to 10 mg of niacin per serving, mostly as NAD and NADP, while plant foods provide about 2 to 5 mg, mostly as nicotinic acid. In grains, a lot of the natural niacin is bound up so that only about 30% is available, though the niacin added to enriched and fortified grain products is highly available.

Values from the NIH ODS niacin fact sheet (USDA FoodData Central). Daily Value is 16 mg. These numbers count preformed niacin only, not the extra niacin your body makes from tryptophan.

Two foods look weak on that table but are worth a second look. Milk and eggs are low in preformed niacin. They still contribute, because they carry tryptophan that your body can turn into NAD+. The ODS gives turkey as an example: a 3-ounce portion of turkey breast provides about 180 mg of tryptophan, which works out to roughly 3 mg of niacin on top of what the table shows.

Foods with NR and NMN

NR and NMN show up in food too, just in small amounts.

• NR in milk. A University of Iowa study measured NAD+ precursors in raw and store-bought cow's milk. Milk typically had about 12 micromoles of precursor vitamins per liter, 60% as nicotinamide and 40% as NR. Conventional milk had more NR than milk sold as organic (Trammell et al., 2016).
• NMN in vegetables and fruit. Researchers at Washington University in St. Louis measured NMN in everyday foods. Edamame, broccoli, cucumber and cabbage had 0.25 to 1.88 mg per 100 grams, avocado and tomato had 0.26 to 1.60 mg, and raw beef and shrimp had 0.06 to 0.42 mg (Mills et al., 2016).

To put that in perspective, the human NMN trials in our NAD+ vs NMN vs NR guide used hundreds of milligrams a day. You won't get anywhere near that from vegetables, and that's fine. Your body leans on niacin and tryptophan from a normal diet, then recycles the nicotinamide it already has.

What about NR and NMN supplements?

NR and NMN are sold as supplements, and they're the precursors most often discussed in longevity circles. The ODS notes that they're not marketed or labeled as sources of niacin, so you won't see them counted toward the niacin line on a label. Small human trials have found that both can raise NAD+ levels in blood or tissue, but none has shown that they slow aging in people. The Buck Institute review says much remains to be learned about how to restore NAD+ levels, whether doing so is safe and whether it helps aging humans (Covarrubias et al., 2021).

We go through the individual NR and NMN trials, the label details and NMN's changing FDA status in NAD+ vs NMN vs NR, so we won't repeat them here. If you're also curious about the enzymes that use NAD+, start with Sirtuins Explained. If you'd like to see one option, OPA makes an NAD+ capsule with nicotinamide riboside, and its product page shows the full label.

Which NAD+ precursor is best?

There isn't a single winner, and the honest answer depends on what you're asking.

• For meeting your basic needs: food. Ordinary amounts of niacin and tryptophan cover baseline NAD+ needs for nearly everyone, according to Bogan and Brenner and the ODS intake data.
• For avoiding the flush: nicotinamide, NR and NMN don't cause it. Nicotinic acid does at higher amounts.
• For longevity research: NR and NMN get the most attention because they enter the salvage route close to NAD+ itself, but human evidence for long-term benefit is still missing.

More isn't automatically better. High-dose niacin products can go well past the 35 mg upper limit, and the ODS describes side effects with high doses, including nausea and liver problems from nicotinic acid taken over months or years and diarrhea from high-dose nicotinamide. If you're thinking about a high-dose B3 product, talk to your clinician first, especially if you take any medication.

Simple ways to keep your NAD+ building blocks covered

• Eat some protein at most meals. Poultry, fish, meat, dairy, eggs, beans and peanuts bring tryptophan, niacin or both.
• Don't forget B2, B6 and iron. The tryptophan route depends on them. Dairy, eggs, leafy greens, poultry and fortified grains help.
• Choose enriched or whole grains. Enriched grain products add highly available niacin.
• Keep up the habits with the best evidence for healthy aging. Regular movement, good sleep and a varied diet matter far more than any one molecule. See our guides on diet and longevity and mitochondrial health.

FAQ

What foods have NAD+ precursors?

Chicken, turkey, fish such as salmon and tuna, beef, pork, peanuts, brown rice and fortified cereals are rich in niacin. Protein foods also bring tryptophan. Cow's milk contains a little NR, and vegetables such as edamame, broccoli and cabbage contain trace amounts of NMN.

Is niacin the same as nicotinamide?

They're both forms of vitamin B3 and both count as niacin on a label. The difference is that nicotinic acid can cause flushing at higher amounts, while nicotinamide (niacinamide) doesn't.

Why does niacin make you flush?

Nicotinic acid widens small blood vessels in the skin. According to the ODS, 30 to 50 mg or more usually causes temporary redness, warmth, tingling or itching on the face, arms and chest. It's considered unpleasant rather than harmful.

Is tryptophan an NAD+ precursor?

Yes. Your body can build NAD+ from tryptophan through the de novo (kynurenine) pathway, mostly in the liver. About 60 mg of tryptophan yields 1 mg of niacin.

Can you get NR or NMN from food?

Only in small amounts. Milk contains NR, and some vegetables and fruits contain up to a couple of milligrams of NMN per 100 grams. Supplements provide far more than food does.

Can you take too much niacin?

From food, it's very unlikely. From supplements and fortified foods, the adult upper limit is 35 mg a day, based on the amounts linked to flushing. Much higher doses can cause more serious side effects, so check with your clinician before taking a high-dose product.

What is the best NAD+ precursor?

For everyday needs, a varied diet with enough protein does the job. Among supplements, NR and NMN are the most studied for NAD+ levels, but neither has been shown to slow aging in people.

Sources

• NIH Office of Dietary Supplements. Niacin: Fact Sheet for Health Professionals. Updated November 18, 2022.
• Covarrubias AJ, Perrone R, Grozio A, Verdin E. NAD+ metabolism and its roles in cellular processes during ageing. Nat Rev Mol Cell Biol. 2021.
• Bogan KL, Brenner C. Nicotinic acid, nicotinamide, and nicotinamide riboside: a molecular evaluation of NAD+ precursor vitamins in human nutrition. Annu Rev Nutr. 2008.
• Bieganowski P, Brenner C. Discoveries of nicotinamide riboside as a nutrient and conserved NRK genes establish a Preiss-Handler independent route to NAD+ in fungi and humans. Cell. 2004.
• Trammell SA, Yu L, Redpath P, Migaud ME, Brenner C. Nicotinamide riboside is a major NAD+ precursor vitamin in cow milk. J Nutr. 2016.
• Mills KF, Yoshida S, Stein LR, et al. Long-term administration of nicotinamide mononucleotide mitigates age-associated physiological decline in mice. Cell Metab. 2016.

Disclosure: OPA Nutrition sells supplements, including products mentioned in this article. This content is for education only and is not medical advice. Statements about dietary supplements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease. Talk to your healthcare provider before using any supplement, especially if you take medication or have a medical condition.