Can Diet Raise NAD+? Tryptophan, Niacin and the De Novo Pathway

The question is whether eating more tryptophan or niacin raises NAD+ in human blood or tissue. The human studies so far measured urinary niacin breakdown products in small controlled diets. None measured blood NAD+ after food niacin or tryptophan. Nicotinamide riboside raised whole-blood NAD+ in several human trials, but no trial compares it with food. This is a Mt. Angel Vitamins company white paper, not a peer-reviewed article.

If you're not a researcher

• No human study we found measured blood NAD+ (nicotinamide adenine dinucleotide) after people ate more tryptophan (an amino acid) or niacin (vitamin B3). The human data stop at urine and at supplements.
• Two small controlled-diet studies in young women tracked urinary niacin breakdown products, not NAD+ itself. One calculation from the first study puts it at about 67 mg of tryptophan per 1 mg of niacin, a little more than the 60 mg the NIH uses.
• Nicotinamide riboside (NR) raised whole-blood NAD+ in human trials. In a 140-person randomized trial, 100, 300 and 1,000 mg a day raised it by 22%, 51% and 142% within two weeks.
• No trial we found compared NR with food niacin, so human data cannot say which one raises blood NAD+ more.
• Established: NR raises blood NAD+ in healthy adults, and urinary niacin markers track tryptophan conversion. Not established: whether more niacin or tryptophan in the diet moves blood or tissue NAD+ in people.
• For the plain-English version, read the NR monograph and the NAD+ pillar.

How the body builds NAD+ from food

Cells make NAD+ along three routes. The de novo route (building NAD+ from simpler parts) starts with tryptophan and runs through the kynurenine pathway, the main enzyme route that breaks tryptophan down, to quinolinic acid (Groth et al., 2021). The Preiss-Handler route starts from nicotinic acid, the acid form of niacin. The salvage route recycles nicotinamide (Christen et al., 2026). The NIH notes that most dietary niacin arrives as nicotinic acid or nicotinamide, and that the body also converts some tryptophan to NAD+ (NIH ODS, 2022).

Christen et al. propose something more specific. Nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN) may feed the Preiss-Handler route only after gut bacteria turn them into nicotinic acid. The authors call this a model and say it is not yet confirmed in humans.

The human studies, by design and size

Each row below is one study. None measured blood NAD+ after eating a niacin-rich or tryptophan-rich food.

Does tryptophan raise NAD+ in people?

Not in blood, as far as we can find. Fukuwatari et al. (2004) fed ten young women a niacin-free purified diet that met Japanese dietary reference intakes, for seven days, and measured their urine. Fukuwatari and Shibata (2007) gave six young women controlled diets with added nicotinamide. Urinary breakdown products rose in a straight line with dose. The upstream intermediates of the tryptophan pathway did not change, quinolinic acid included. That second result matters. Extra nicotinamide in the diet did not change how much the body built de novo.

Grades: urinary niacin breakdown products track tryptophan conversion, Preliminary (two small controlled-diet studies of 10 and 6 women). Blood NAD+ rising after dietary tryptophan, Insufficient (no human study has measured it).

Does niacin raise NAD+ in people?

No human trial we found gave niacin and measured NAD+ in blood or tissue. The NIH says blood niacin levels are unreliable as status markers. The sensitive measures are urinary N1-methylnicotinamide and 2-pyridone, and a whole-blood NAD+ to NADP ratio below 130 suggests deficiency (NIH ODS, 2022).

Observational human data use those markers. In a cohort of 660 kidney transplant recipients, higher 24-hour excretion of the two urinary markers went with lower all-cause mortality over a median 5.4 years (hazard ratio 0.61; Deen et al., 2020). Intake was not controlled, so this is an association. In people with carcinoid syndrome, whole-blood niacin number was low in 10 of 36, more often than in controls (Shah et al., 2005). That study concerns a disease that diverts tryptophan toward serotonin, not diet.

Test-tube work points the same way but does not settle it. In whole blood ex vivo, nicotinic acid was a potent NAD+ booster, while NR, NMN and nicotinamide were not (Christen et al., 2026). That shows what happens in a tube, not what a person absorbs.

Grades: urinary markers as niacin status, Moderate (NIH-endorsed markers, observational human data). Blood NAD+ response to niacin in people, Insufficient (no in vivo human trial; ex vivo only).

What the NIH sets for niacin, and what it does not set for tryptophan

For adults, the NIH recommends 16 mg niacin equivalents (NE) a day for men and 14 mg NE for women. Pregnancy is 18 mg NE and lactation is 17 mg NE. One NE equals 1 mg of niacin or 60 mg of tryptophan. The adult upper intake level is 35 mg a day, set from skin flushing (NIH ODS, 2022).

The NIH publishes no fact sheet on tryptophan, so this page gives no tryptophan RDA or upper limit. Nicotinamide does not cause flushing, but the NIH reports nausea, vomiting and signs of liver toxicity at 3,000 mg a day (NIH ODS, 2022).

Which foods supply the most NAD+ precursors?

By niacin content, the NIH gives the clearest answer. Poultry, beef and fish supply about 5 to 10 mg of niacin per serving, mostly as NAD and NADP. Nuts, legumes and grains supply about 2 to 5 mg per serving, mostly as nicotinic acid, and in some grain products only about 30% is absorbed (NIH ODS, 2022). That ranks foods by niacin, not by NAD+ response.

Milk is the one food where NAD+ precursors were measured directly. Ummarino et al. (2016) found NR, NMN and NAD+ in human and donkey milk, with different patterns in other milks. Ultra-high-temperature processing destroyed the NR in bovine milk, while pasteurization did not. That was a laboratory assay of milk samples, not a study in people, and the abstract gives no concentrations.

Only one food-level human trial moved NAD+-pathway metabolites in blood. Barrong et al. (2024) randomized overweight adults to four weeks of liquid vinegar, 2.95 g of acetic acid a day, or a tablet with almost none. Serum nicotinamide and the salvage pathway rose in the vinegar group. That was a secondary outcome of a trial built around mood scores, and vinegar is not a niacin source.

Grades: food niacin and blood NAD+ response, Insufficient. Vinegar and serum nicotinamide, Preliminary (one small randomized trial, 29 entered, secondary outcome).

Is the de novo NAD+ pathway important in people?

The pathway runs in people, and its intermediates move. Quinolinic acid rose in 24 healthy men after a single endurance session (Joisten et al., 2020), though NAD+ was not measured. No study we found shows how much blood NAD+ the de novo route supplies. Grade: Insufficient for the human share.

The evidence that the route matters comes from cells and animals. In cultured human astrocytes and neurons, blocking the kynurenine enzymes lowered intracellular NAD+ in a dose-dependent way (Braidy et al., 2011). In guinea pigs on niacin-deficient purified diets, blood NAD+ fell by 32 to 44% over seven weeks (Thorn et al., 2007). Both are animal or cell work. Neither tells us how much human blood NAD+ comes from tryptophan.

Is it better to take NR or eat more niacin?

The human data cannot rank them, but the evidence is lopsided. NR has been measured in human blood in several randomized trials and one open-label pharmacokinetic study. Airhart et al. (2017) gave eight healthy volunteers NR, from 250 mg up to 1,000 mg twice a day, and whole-blood NAD+ roughly doubled at steady state. Conze et al. (2019) enrolled 140 people and found the 22%, 51% and 142% rises described above, with no flushing reported and no significant adverse-event difference from placebo. Christen et al. (2026) randomized 65 healthy adults and found NR and NMN raised circulating NAD+ similarly over 14 days. For the full trial record and the doses, see the trial record and NMN and NR doses against the trials.

Tissue data point the same way. In 13 overweight or obese adults, 1,000 mg of NR a day for six weeks raised NAD+ metabolites in skeletal muscle compared with placebo (Remie et al., 2020). In 22 healthy older adults, 500 mg twice a day for six weeks raised NAD(H) in plasma vesicles of neuronal origin (Vreones et al., 2022), a surrogate rather than brain tissue. In a 30-person trial in newly diagnosed patients, 1,000 mg for 30 days raised brain NAD+ measured by magnetic resonance spectroscopy, though the response varied (Brakedal et al., 2022).

What the human data cannot do is compare NR with food niacin. No trial we found did that, and none measured blood NAD+ after food niacin. Whole-blood NAD+ may also be a weak marker of lifestyle. Trętowicz et al. (2026) reported that whole-blood NAD+ stayed stable across seven human cohorts with age and lifestyle interventions, and changed only with NR. We read the abstract only, so their cohort sizes and lifestyle arms are not verified here.

Grades: NR raising blood NAD+, Strong (several randomized trials, consistent direction). NR raising muscle or brain NAD+ metabolites, Moderate (two small randomized trials). Food niacin against NR head to head, Insufficient (no trial).

What is established, what is proposed, and what would settle it

Established. NR raises whole-blood NAD+ in healthy adults at 100 to 1,000 mg a day within two weeks (Conze et al., 2019; Christen et al., 2026). Urinary niacin breakdown products rise with tryptophan conversion and with nicotinamide intake in small controlled-diet studies (Fukuwatari et al., 2004; Fukuwatari and Shibata, 2007).

Proposed. NR and NMN may work partly through gut bacteria that make nicotinic acid (Christen et al., 2026). Dietary tryptophan may supply a measurable share of blood NAD+. Nobody has measured that share in people.

What would settle it. A controlled-feeding trial with three arms (a niacin-rich diet, a tryptophan-enriched diet and NR), measuring whole-blood NAD+, urinary niacin markers and labeled tryptophan over several time points, with enough participants for a power calculation. This is a design suggestion, not a finding.

Limits of this paper

This is a Mt. Angel Vitamins company white paper, not a peer-reviewed article. The PubMed search ran on October 22, 2026. Several results rest on abstracts because full texts were not available, and the whole-blood cohort study (Trętowicz et al., 2026) is the clearest case. Two NR trials have authors affiliated with companies that make or study NAD+ precursors: Conze et al. with ChromaDex and Christen et al. with Nestlé Research. Both report their own results.

Glossary

• NAD+: nicotinamide adenine dinucleotide, a coenzyme that carries electrons in energy and repair reactions.
• NADP: a phosphorylated relative of NAD+, used mostly in building reactions.
• De novo route: making NAD+ from tryptophan, starting from simpler parts.
• Kynurenine pathway: the main enzyme route that breaks tryptophan down and feeds the de novo route.
• Quinolinic acid: a kynurenine-pathway intermediate that enters the de novo route.
• Preiss-Handler route: making NAD+ from nicotinic acid, one form of niacin.
• Salvage route: recycling nicotinamide back into NAD+.
• Niacin equivalent (NE): the NIH unit; 1 mg niacin or 60 mg tryptophan.
• N1-methylnicotinamide and 2-pyridone: urinary breakdown products used to gauge niacin status.
• Niacin number: whole-blood NAD+ to NADP ratio, times 100.
• Nicotinamide riboside (NR): a form of vitamin B3 that cells convert to NAD+.
• Nicotinamide mononucleotide (NMN): a precursor one step closer to NAD+ than NR.
• Open-label: participants and staff know which treatment is being given.

References

1. Fukuwatari T, et al. J Nutr Sci Vitaminol. 2004;50(6):385 to 391. PMID 15895512. https://doi.org/10.3177/jnsv.50.385
2. Fukuwatari T, Shibata K. Int J Vitam Nutr Res. 2007;77(4):255 to 262. PMID 18271280. https://doi.org/10.1024/0300-9831.77.4.255
3. Deen CPJ, et al. Nutrients. 2020;12(7):2059. PMID 32664445. https://doi.org/10.3390/nu12072059
4. Shah GM, et al. Am J Gastroenterol. 2005;100(10):2307 to 2314. PMID 16181385. https://doi.org/10.1111/j.1572-0241.2005.00268.x
5. Christen S, et al. Nat Metab. 2026;8(1):62 to 73. PMID 41540253. https://doi.org/10.1038/s42255-025-01421-8
6. Barrong H, et al. Nutrients. 2024;16(14):2305. PMID 39064748. https://doi.org/10.3390/nu16142305
7. Joisten N, et al. Exerc Immunol Rev. 2020;26:24 to 42. PMID 32139353.
8. Trętowicz MM, et al. Nat Metab. 2026;8(6):1282 to 1290. PMID 42135539. https://doi.org/10.1038/s42255-026-01537-5
9. Airhart SE, et al. PLoS One. 2017;12(12):e0186459. PMID 29211728. https://doi.org/10.1371/journal.pone.0186459
10. Conze D, et al. Sci Rep. 2019;9:9772. PMID 31278280. https://doi.org/10.1038/s41598-019-46120-z
11. Remie CME, et al. Am J Clin Nutr. 2020;112(2):413 to 426. PMID 32320006. https://doi.org/10.1093/ajcn/nqaa072
12. Vreones M, et al. Aging Cell. 2022;22(1):e13754. PMID 36515353. https://doi.org/10.1111/acel.13754
13. Brakedal B, et al. Cell Metab. 2022;34(3):396 to 407. PMID 35235774. https://doi.org/10.1016/j.cmet.2022.02.001
14. Thorn SL, Young GS, Kirkland JB. Br J Nutr. 2007;98(1):78 to 85. PMID 17391557. https://doi.org/10.1017/S0007114507707663
15. Braidy N, Guillemin GJ, Grant R. Int J Tryptophan Res. 2011;4:29 to 37. PMID 22084601. https://doi.org/10.4137/IJTR.S7052
16. Groth B, Venkatakrishnan P, Lin SJ. Front Mol Biosci. 2021;8:686412. PMID 34095234. https://doi.org/10.3389/fmolb.2021.686412
17. Ummarino S, et al. Food Chem. 2016;221:161 to 168. PMID 27979136. https://doi.org/10.1016/j.foodchem.2016.10.032
18. NIH Office of Dietary Supplements. Niacin: Health Professional Fact Sheet, updated November 18, 2022. https://ods.od.nih.gov/factsheets/Niacin-HealthProfessional/

Next reads

• NR monograph: what the ingredient is, how its blood response is measured, and which trials covered it.
• NMN vs NR: which NAD+ precursor should you take?: the head-to-head comparison of the two precursors.
• Best NMN + NR supplements in the US (2026 buyer's guide): what to check on a label, and how labeled doses compare with the trials.

Related reading

• the 1989 tryptophan outbreak and the quality rules that followed
• the niacin history behind the tryptophan route to NAD

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