Does Your Body Divert Tryptophan From Melatonin to Make NAD+?

Tryptophan is often described as a sleep nutrient — the amino acid in turkey that supposedly makes you drowsy. But your body has a different priority. The vast majority of dietary tryptophan never reaches the melatonin pathway. It gets routed to NAD+ production instead, a molecule your cells need for energy metabolism and DNA repair.

This article covers the biochemical competition between two pathways that share one starting ingredient: the kynurenine pathway (which produces NAD+) and the serotonin pathway (which produces melatonin). It explains what determines the balance, what inflammation does to that balance, and what recent human evidence shows about the consequences for sleep.

This is one mechanism within the broader pattern of metabolic sleep disruption — where energy metabolism and sleep regulation compete for the same biological resources.

Why Does 95% of Your Tryptophan Go to Nicotinamide Adenine Dinucleotide (NAD+) Instead of Melatonin?

Tryptophan enters the body through protein-rich food and reaches a branch point. Two competing enzyme families determine where it goes.

The first route is controlled by TDO (tryptophan 2,3-dioxygenase) in the liver and IDO in peripheral tissues. Both enzymes feed tryptophan into the kynurenine pathway, which produces NAD+ through a multi-step conversion: tryptophan to kynurenine, then through several intermediates to quinolinic acid, which is converted to NAD+ by the enzyme QPRT (quinolinate phosphoribosyltransferase). This is called de novo NAD+ synthesis — building NAD+ from scratch using tryptophan as the raw material (Zhang et al., 2024).

TPH (tryptophan hydroxylase) controls the second route, converting tryptophan to 5-HTP, then to serotonin, and eventually to melatonin in the pineal gland.

Under normal conditions, the kynurenine pathway consumes approximately 95% of available tryptophan. The serotonin-to-melatonin route receives 1-2% (Xie et al., 2026). This ratio exists because NAD+ is a metabolic priority: it serves as a cofactor for hundreds of enzymatic reactions, including energy production in mitochondria, DNA damage repair via PARP enzymes, and immune cell function.

TDO is constitutively active in the liver and responds to cortisol — meaning stress hormones increase baseline tryptophan routing toward kynurenine. IDO is active in immune and peripheral tissues and is upregulated by inflammatory cytokines. Between the two enzymes, the kynurenine pathway maintains priority access to tryptophan that melatonin synthesis cannot override.

The melatonin pathway receives what remains after kynurenine demand is met. Under stable, low-inflammation conditions, that remainder is enough. But anything that increases kynurenine pathway activity — stress, immune activation, aging — cuts into a supply that was already small.

Does Inflammation Redirect Your Tryptophan Away From Sleep?

That baseline split is the starting point. Inflammation makes it worse.

When the immune response activates, pro-inflammatory cytokines — especially interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha) — induce IDO1 expression in immune and peripheral tissues (Zhang et al., 2024). IDO1 accelerates tryptophan-to-kynurenine conversion, pulling more tryptophan out of circulation and away from the serotonin-melatonin route.

This is not limited to acute infections. Chronic, low-grade immune activation sustains elevated kynurenine-to-tryptophan (Kyn/Trp) ratios over weeks and months. A 2025 human cohort study of people with common variable immunodeficiency (CVID) — a condition characterized by chronic immune activation — used mass spectrometry to measure serum kynurenine metabolites across two independent cohorts (n=40 people with CVID vs. n=60 healthy controls in discovery; n=53 people with CVID in validation). People with CVID showed elevated Kyn/Trp ratios in both cohorts, correlated with markers of monocyte and macrophage activation (soluble CD14, CD163, and neopterin) (Jorgensen et al., 2025). The IDO-driven tryptophan diversion was embedded within broader immune activation — not an isolated event.

The sleep consequences are measurable. A cross-sectional study of 160 people — including 68 currently depressed, 26 previously depressed, and 66 never depressed — found that among those with current depression, sleep disturbance was associated with a lower neuroprotective kynurenine ratio (kynurenic acid-to-quinolinic acid), indicating a tilt toward the neurotoxic branch of kynurenine metabolism. This association held after adjusting for age, sex, BMI, and depression severity (adjusted beta = -0.30, p = 0.02). In the same group, sleep disturbance was independently associated with elevated C-reactive protein (adjusted beta = 0.33, p = 0.02) — linking inflammation, kynurenine imbalance, and poor sleep in the same individuals at the same time. No associations between sleep disturbance and kynurenine ratios were detected in the remitted or never-depressed groups, suggesting that active inflammatory context is needed for these kynurenine pathway changes to manifest as sleep disruption (Cho et al., 2017).

Inflammation both reduces tryptophan available for melatonin and generates neurotoxic intermediates. The kynurenine pathway metabolites that accumulate — particularly 3-hydroxykynurenine and quinolinic acid — are themselves neurotoxic. The immune response consumes the raw material for sleep and produces compounds that can impair brain function.

Does the Diverted Tryptophan Even Produce Nicotinamide Adenine Dinucleotide (NAD+) Successfully?

If tryptophan is being diverted from melatonin to make NAD+, the assumption is that at least NAD+ gets produced. That assumption may be wrong during inflammation.

Quinolinate — the precursor to NAD+ in the kynurenine pathway — accumulates in macrophages, microglia, and dendritic cells during immune activation. But whether this quinolinate is efficiently converted to NAD+ remains what researchers call "the unresolved question." The bottleneck is QPRT, the enzyme that converts quinolinate to NAD+. QPRT activity may be restricted, slowing the processing of the quinolinate that accumulates during active immune responses (Moffett et al., 2020).

A 2024 study using Winnie mice — an animal model of chronic intestinal inflammation — mapped gene expression across both colon and brain tissue. In inflamed colon tissue, kynurenine pathway genes (Ido1, Kynu, Mao-b) were upregulated, but the genes needed to complete NAD+ biosynthesis (Nmnat2, Nmnat3, Nmrk1, Nadsyn1) were downregulated (Devereaux et al., 2024). Tryptophan was funneled into kynurenine intermediates, but the conversion to NAD+ was incomplete.

There is also a transport dimension. In the inflammation model, brain tryptophan metabolite levels dropped — the authors suggest this may reflect disrupted transport of tryptophan and its metabolites across the blood-brain barrier, reducing raw material available for brain melatonin and NAD+ production (Devereaux et al., 2024).

The net result during sustained inflammation in this animal model: melatonin precursors are depleted, NAD+ is not reliably produced, and neurotoxic intermediates (quinolinate, 3-hydroxykynurenine) accumulate. The tryptophan is lost from the melatonin pathway without completing the NAD+ pathway.

If your sleep is disrupted and you also deal with ongoing inflammation, gut issues, or chronic immune activation, tryptophan competition might be one piece of the picture. Metabolic sleep disruption might involve NAD+ decline, blood sugar instability, or mitochondrial changes working alongside tryptophan diversion. Identifying which combination might be active in your situation is the starting point.

Find out which causes might be driving your 3am wakeups →

Can Kynurenine Disrupt Your Circadian Clock Independent of Melatonin?

The sections above describe how kynurenine pathway activation depletes melatonin’s precursor. But a 2026 study provides evidence for a second, independent mechanism: kynurenine may alter circadian timing on its own.

Xie et al. (2026) used genetic variants as natural experiments to examine whether kynurenine metabolite levels affect sleep phenotypes. Genetically predicted plasma kynurenine was associated with delayed L5 timing (the timing of the least-active 5-hour rest period), with an odds ratio of 1.194 (95% CI: 1.025-1.389, p = .022). Higher kynurenine corresponded to a later rest-activity rhythm.

This association did not survive false discovery rate correction, marking it as suggestive rather than established. But the directionality was consistent: the reverse analysis found no effect from sleep phenotypes back onto kynurenine metabolite levels. The direction of influence appears to run from kynurenine metabolites to sleep, not the other way around.

The same research group ran cell experiments showing that L-kynurenine upregulated Bmal1 mRNA in rat fibroblasts (Rat-1 cells) at multiple circadian timepoints. Bmal1 is a core component of the molecular clock that governs circadian rhythms in every cell (Xie et al., 2026).

This points to two mechanisms by which kynurenine pathway activation may disrupt sleep:

1. Melatonin precursor depletion — tryptophan consumed by the kynurenine pathway is unavailable for melatonin synthesis (effect on sleep via reduced melatonin)
2. Clock gene modulation — kynurenine itself alters Bmal1 expression, changing circadian timing independent of melatonin

The second mechanism has a practical implication: even if melatonin were supplied through supplementation, kynurenine accumulation could still disrupt circadian timing through Bmal1 modulation. Melatonin supplementation may not fully compensate for kynurenine-driven circadian disruption.

Can Supplying Nicotinamide Adenine Dinucleotide (NAD+) Through Other Routes Spare Tryptophan for Melatonin?

Kynurenine metabolism is one of two routes your body uses to produce NAD+. The other is the salvage pathway, which recycles nicotinamide (a form of vitamin B3) back into NAD+ via the enzyme NAMPT. Niacin, nicotinamide riboside (NR), and NMN all feed into this salvage pathway without consuming tryptophan (Zhang et al., 2024).

The biochemical logic is direct: if you supply enough NAD+ through the salvage route, the body’s demand for de novo NAD+ synthesis from tryptophan decreases. Less demand on the kynurenine pathway means less IDO/TDO activity pulling tryptophan away from melatonin. More tryptophan remains available for TPH, serotonin, and melatonin.

Niacin is inexpensive and widely available. NR and NMN are sold as supplements targeting NAD+ restoration. All three bypass the kynurenine pathway.

There is a complication. Li et al. (2017) identified a feedback loop where melatonin itself induces IDO1 expression through JNK-FoxO1 activity in neuronal cells (PC12 cell model). If restoring melatonin production through tryptophan sparing also reactivates IDO1, the kynurenine pathway could increase activity again. The two pathways appear to have built-in oscillation — melatonin feeds back to activate the pathway that competes with its own production.

The evidence gap is specific: no randomized controlled trial has measured whether niacin, NR, or NMN supplementation increases melatonin levels in humans. The biochemical rationale is sound — the salvage pathway can supply NAD+ without consuming tryptophan, and reduced kynurenine pathway demand should free tryptophan for melatonin. But this remains a hypothesis with strong mechanistic support rather than an established finding.

Community reports describe improved sleep with niacin supplementation, but anecdotal evidence cannot distinguish between tryptophan-sparing effects and other mechanisms (niacin also affects prostaglandins, vasodilation, and other pathways).

Frequently Asked Questions

Does Nicotinamide Adenine Dinucleotide (NAD+) Help With Sleep?

SIRT1, an NAD+-dependent enzyme, modulates core circadian clock proteins. Declining NAD+ with age correlates with deteriorating sleep quality. But the de novo pathway that produces NAD+ from tryptophan competes with melatonin production for the same substrate — and during inflammation, that conversion may stall at toxic intermediates, reducing both melatonin and NAD+ output (Zhang et al., 2024). Supporting NAD+ through salvage pathway precursors (niacin, NR, NMN) may bypass this competition. For the broader picture of how NAD+ decline connects to sleep disruption, see Metabolic Sleep Disruption.

Does Inflammation Reduce Melatonin Production?

Acute infections cause temporary IDO activation that resolves when the immune response subsides. Chronic, low-grade inflammation is different — persistent immune activation from gut dysbiosis, autoimmune conditions, or aging-related inflammation keeps IDO elevated for months, sustaining the tryptophan drain away from melatonin (Cho et al., 2017; Jorgensen et al., 2025).

Can Taking Niacin Help Your Body Make More Melatonin?

Niacin comes in several forms: nicotinic acid (causes flushing above ~50 mg), nicotinamide (no flushing but inhibits sirtuins at high doses), NR, and NMN. All feed the salvage pathway without requiring tryptophan. The gap is in measurement — no study has administered any of these and measured circulating melatonin as an endpoint (Zhang et al., 2024; Li et al., 2017).

Does Nicotinamide Adenine Dinucleotide (NAD+) Affect Your Circadian Rhythm?

Two mechanisms connect NAD+ metabolism to circadian function: NAD+ oscillates in a circadian pattern and is required by SIRT1 to regulate clock proteins, while kynurenine — the intermediate produced during tryptophan-to-NAD+ conversion — modulates the clock gene Bmal1. Both pathways converge on disrupted circadian timing through different molecular targets (Xie et al., 2026).

Related Reading

• Metabolic Sleep Disruption: How Metabolic Impairment Fragments Sleep — the pillar article for metabolic sleep disruption, covering glucose regulation, cortisol rhythm, mitochondrial stress, NAD+ loss, and fat metabolism
• Which Nicotinamide Adenine Dinucleotide Precursor Improves Sleep — Nicotinamide Mononucleotide or Nicotinamide Riboside? — NMN and NR sleep evidence, timing, safety, and human trial differences
• Does NMN Cause Insomnia? What Timing and Dose Matter — NMN timing, dose, circadian effects, and sleep continuity data
• Does Apigenin Protect Your NAD+ and Improve Sleep Through CD38 Inhibition? — CD38 inhibition, NAD+ depletion with age, and apigenin sleep evidence
• Why Does Sleep Repair Your DNA — And Burn Through Your NAD+ to Do It? — PARP1, sleep pressure, DNA repair, and NAD+ demand during sleep
• Does Your Gut Decide Whether Your NAD+ Supplement Works? — gut microbiome conversion of NAD+ precursors and why supplement response varies
• Does NAD+ IV Therapy Improve Sleep? What the Evidence Shows — IV NAD+ evidence, safety, infusion effects, and comparison with oral precursors
• Why Does NAD+ Drop Faster in Women After 40 — And What Does That Mean for Sleep? — menopause, ovarian aging, NAD+ decline, and sleep disruption after 40

References

1. Cho, H. J., Savitz, J., Dantzer, R., Teague, T. K., Drevets, W. C., & Irwin, M. R. (2017). Sleep disturbance and kynurenine metabolism in depression. Journal of Psychosomatic Research, 99, 1-7. https://pubmed.ncbi.nlm.nih.gov/28712413/

2. Devereaux, J., Robinson, A. M., Stavely, R., Davidson, M., Dargahi, N., Ephraim, R., Kiatos, D., Apostolopoulos, V., & Nurgali, K. (2024). Alterations in tryptophan metabolism and de novo NAD+ biosynthesis within the microbiota-gut-brain axis in chronic intestinal inflammation. Frontiers in Medicine, 11, 1379335. https://pubmed.ncbi.nlm.nih.gov/39015786/

3. Jorgensen, S. F., Braadland, P. R., Ueland, T., Fraz, M. S. A., Michelsen, A. E., Holm, K., Osnes, L. T., Troseid, M., Ueland, P. M., Fevang, B., Aukrust, P., & Hov, J. R. (2025). Tryptophan-kynurenine metabolites associate with inflammation and immunologic phenotypes in common variable immunodeficiency. The Journal of Allergy and Clinical Immunology, 156(3), 814-824.e11. https://pubmed.ncbi.nlm.nih.gov/40378971/

4. Li, Y., Hu, N., Yang, D., Oxenkrug, G., & Yang, Q. (2017). Regulating the balance between the kynurenine and serotonin pathways of tryptophan metabolism. The FEBS Journal, 284(6), 948-966. https://pubmed.ncbi.nlm.nih.gov/28118532/

5. Moffett, J. R., Arun, P., Puthillathu, N., Vengilote, R., Ives, J. A., Badawy, A. A.-B., & Namboodiri, A. M. (2020). Quinolinate as a marker for kynurenine metabolite formation and the unresolved question of NAD+ synthesis during inflammation and infection. Frontiers in Immunology, 11, 31. https://pubmed.ncbi.nlm.nih.gov/32153556/

6. Xie, Q., Liu, G., & Liu, X. (2026). Cerebrospinal fluid, plasma tryptophan, kynurenine, and kynurenate with sleep phenotypes: A bidirectional Mendelian randomization analysis. International Journal of Tryptophan Research, 19, 11786469261441903. https://pubmed.ncbi.nlm.nih.gov/42016613/

7. Zhang, J., Liu, Y., Zhi, X., Xu, L., Tao, J., Cui, D., & Liu, T. F. (2024). Tryptophan catabolism via the kynurenine pathway regulates infection and inflammation: From mechanisms to biomarkers and therapies. Inflammation Research, 73(6), 979-996. https://pubmed.ncbi.nlm.nih.gov/38592457/

Written by Kat Fu, M.S., M.S. · Last reviewed: May 2026 · 7 references cited