NAD+ and the circadian clock: the NAMPT feedback loop

Prepared by: Research Desk. Sources are linked for verification.

NAD+ is often described as though each cell holds a fixed amount of it. Two papers published back to back in Science in 2009 challenged that picture. In mouse tissue and mouse cells, NAD+ levels rose and fell on a daily rhythm. The circadian clock drove that rhythm, and the rhythm in turn fed back on the clock itself [1][2].

This explainer walks through that loop one step at a time. It covers the experiments behind each step, the later studies that extended it, and the point where the evidence stops. For the wider biochemistry of NAD+, see our NAD+ guide.

The clock in brief

Mammalian cells keep time with a transcription-translation feedback loop. This loop synchronises behaviour and metabolism with the light-dark cycle [1]. The core transcription factors are CLOCK and BMAL1. They work as a pair, CLOCK:BMAL1, and switch on clock-controlled genes.

Nakahata and colleagues had earlier shown that CLOCK is more than a transcription factor. It is also a histone acetyltransferase. Its activity is counterbalanced by SIRT1, a histone deacetylase that depends on NAD+ [2]. That detail matters for everything below. An enzyme that needs NAD+ sits right next to the clock's core machinery.

Step 1: the clock switches on NAMPT

NAMPT (nicotinamide phosphoribosyltransferase) is the rate-limiting enzyme in the NAD+ salvage pathway. This is the route cells use to recycle nicotinamide back into NAD+ [1][2]. Both 2009 groups reported that NAMPT expression is under circadian control:

• Ramsey et al. found that CLOCK binds to the Nampt gene and up-regulates it in mice [1].

• Nakahata et al. reported that CLOCK:BMAL1 regulates the circadian expression of NAMPT in mouse embryo fibroblasts [2].

For background on the enzyme itself, see NAMPT explained and the NAD+ salvage pathway.

Step 2: NAD+ levels oscillate

If NAMPT output rises and falls, NAD+ supply should follow. Both papers reported exactly this.

Ramsey et al. found that NAMPT and NAD+ levels both showed circadian oscillations in mice, regulated by the core clock machinery [1]. Nakahata et al. reported that intracellular NAD+ levels cycled with a 24-hour rhythm driven by the circadian clock [2].

Step 3: SIRT1 closes the loop

SIRT1 uses NAD+ as a cosubstrate. So when NAD+ levels swing over the day, SIRT1 activity can swing with them. SIRT1 then acts back on the clock:

• Suppressing CLOCK:BMAL1. In Ramsey et al., SIRT1 suppressed CLOCK:BMAL1. Inhibiting NAMPT released that suppression and promoted oscillation of the clock gene Per2 [1].

• Regulating its own supply. Nakahata et al. found SIRT1 recruited to the Nampt promoter. They concluded that SIRT1 contributes to the circadian synthesis of its own coenzyme [2].

The authors summarised the result as a feedback loop linking NAMPT/NAD+ with SIRT1/CLOCK:BMAL1 [1]. Nakahata's group called it "an interlocked transcriptional-enzymatic feedback loop" connecting cellular metabolism and circadian rhythms [2].

In plain terms, the loop runs like this. The clock makes NAMPT. NAMPT makes NAD+. NAD+ powers SIRT1. SIRT1 tunes the clock.

For how sirtuins use NAD+ more generally, see NAD+ and sirtuins.

How the loop was tested: blocking NAMPT

A loop like this is only convincing if breaking one link disturbs the others. Both groups did this by inhibiting NAMPT.

Nakahata et al. used the specific NAMPT inhibitor FK866 in mouse embryo fibroblasts. They reported that NAMPT is required to modulate circadian gene expression [2]. Ramsey et al. reported that NAMPT inhibition changed Per2 oscillation by releasing CLOCK:BMAL1 from SIRT1 suppression [1].

FK866 is used here purely as a laboratory tool for testing mechanism.

Extensions: chromatin and redox state

Later work added detail to how NAD+ rhythms reach the genome and how redox state fits in.

Histone methylation. Aguilar-Arnal et al. studied MLL1, a histone methyltransferase that helps recruit CLOCK-BMAL1 to chromatin [3]. In mouse liver, they reported that:

• MLL1 is acetylated at two conserved residues, K1130 and K1133.

• This acetylation is cyclic and controlled by both the clock and SIRT1.

• Levels of MLL1 acetylation and H3K4 trimethylation at circadian promoters depended on circadian NAD+ levels.

NADH as a brake. NAD+ also exists in a reduced form, NADH. Levine et al. studied mice fed a calorie-restricted diet only at night [4]. These animals showed reduced body temperature and elevated liver NADH during the daytime.

The researchers then expressed a bacterial NADH oxidase (LbNOX) to uncouple nutrient state from NADH redox state. This raised daytime body temperature and increased blood and liver acyl-carnitines. It also induced oxidative gene networks controlled by BMAL1 and PPARα [4]. Their enzymatic analyses reported that NADH inhibits SIRT1. This links the cell's energy state to clock-driven transcription [4].

That makes the NAD+/NADH balance part of the story, not just total NAD+. See the NAD+/NADH ratio explained.

Wider research threads

Several reviews and experimental studies place the loop in broader contexts. Each is framed as a research question:

• Liver metabolism. A 2022 review describes sirtuins and clock genes as metabolic regulators in the liver. It notes that knockouts of either sirtuins or clock genes produce obesity with a fatty-liver phenotype in models [5].

• Telomeres. A 2020 review reports that SIRT1 contributes to the circadian clock by mediating CLOCK/BMAL1 complex formation, BMAL1 transcription and PER2 disruption. It also discusses SIRT1's role in telomere homeostasis [6].

• Skeletal muscle. A 2023 experimental (non-human) study reported that heavy-load exercise disrupted the rhythm of Bmal1 between ZT0 and ZT24. The rhythm of Clock was not restored between ZT0 and ZT72. The study also reported abnormal NAMPT/NAD+/SIRT1 axis protein expression [7].

What the evidence shows, and what it doesn't

None of the sources on this page measured the NAMPT-NAD+-SIRT1 loop in humans. None tested whether the timing of any NAD+ precursor intake matters in people. The mechanism is well supported in mice and cultured cells. Its relevance to human physiology is still an open research question.

This has one practical implication for reading data. If NAD+ varies with time of day in animals, the sampling time is a fair question to ask of any NAD+ measurement. Our guide to reading an NAD+ test report covers sample types and units. For how precursors are classified in the U.S., see our regulatory explainer.

Further reading on chronobiology

Readers who want to go deeper than a single explainer can turn to a good chronobiology or metabolic biochemistry book. Useful neutral criteria for choosing one:

• Publication date. Books published before 2009 predate the NAMPT feedback loop entirely.

• Citations. Look for books that cite primary papers rather than summarising other popular books.

• Evidence labels. The best books separate mouse, cell and human findings clearly, chapter by chapter.

• Format. Textbooks give pathway diagrams and enzyme detail. Popular science titles give narrative. Check the table of contents for coverage of sirtuins and redox metabolism.

• Price and edition. Older editions are cheaper but may miss newer work, such as the NADH-SIRT1 findings.

Our evidence-graded NAD+ reading list applies these same criteria to titles on sirtuins and aging.

Frequently asked questions

Does NAD+ really follow a daily rhythm?

In mice and mouse cells, yes. Two 2009 studies reported clock-driven NAD+ oscillations, including a 24-hour rhythm in mouse embryo fibroblasts [1][2]. The sources here do not include equivalent human measurements.

What makes this a feedback loop rather than a one-way effect?

The clock drives NAMPT and therefore NAD+. NAD+ then powers SIRT1, which acts back on CLOCK:BMAL1 [1]. SIRT1 is also recruited to the Nampt promoter, so it helps regulate production of its own coenzyme [2].

What is FK866?

FK866 is a specific inhibitor of NAMPT used in laboratory experiments. Nakahata et al. used it to show that NAMPT is required to modulate circadian gene expression in cultured mouse cells [2].

How does NADH fit in?

In a mouse feeding study, enzymatic analyses reported that NADH inhibits SIRT1 [4]. This suggests the cell's redox state can feed into clock-driven transcription alongside NAD+ levels.

Related on this site

• NAD+, measured properly

• NAD+ explained: biochemistry, precursors, testing and human evidence

• NAMPT explained: the rate-limiting enzyme in NAD+ recycling

• NAD+ and sirtuins: how the enzymes use NAD+ and what research examined

• The NAD+ salvage pathway: how cells recycle NAD+

• The NAD+/NADH ratio explained: redox balance and how it is measured

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Last updated: 26 October 2026.

Not medical advice. This page reports published research and regulatory records for information only.

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