Longevity / CD38 Inhibition and Apigenin: Why It Matters for NAD+

CD38 Inhibition and Apigenin: Why It Matters for NAD+

Written by

Sophie Chabloz

If you’ve read about NMN supplementation, you’ve probably heard that NAD+ declines with age and that precursor supplementation can help restore it. That’s accurate, but it addresses only half the problem. A significant driver of age-related NAD+ depletion isn’t just insufficient production. It’s an enzyme called CD38 that consumes NAD+ at an accelerating rate as you get older. Understanding what CD38 does, and why the flavonoid apigenin can slow it down, changes how you think about a complete NAD+ strategy.

In this article:

What CD38 is and how it degrades NAD+
Why ageing drives CD38 expression higher
Apigenin as a CD38 inhibitor: mechanism and evidence
Dietary sources versus supplemental apigenin
Combining CD38 inhibition with NMN in a full strategy
Practical guidance: dosing, timing, and cautions
Where to go next

What CD38 is and how it degrades NAD+

CD38 is a multifunctional enzyme found on the surface of many cell types, including immune cells, muscle cells, and neurons. Its primary enzymatic role is as a glycohydrolase: it cleaves NAD+ into smaller signalling molecules, principally cyclic ADP-ribose (cADPR) and nicotinamide. Cyclic ADP-ribose plays a legitimate role in intracellular calcium signalling, particularly in immune cell activation, and CD38-derived signals are important for certain immune responses. The problem is efficiency, or more precisely the lack of it.

For each molecule of cADPR that CD38 generates, it consumes anywhere from 25 to 100 molecules of NAD+. It’s extraordinarily wasteful relative to the signal it produces. In a young, metabolically robust cell, this consumption can be offset by active NAD+ biosynthesis through the salvage pathway and through NAMPT-mediated recycling. As those biosynthetic pathways slow with age, CD38’s drain becomes progressively harder to compensate for.

Why most NAD+ discussions miss CD38

For years, the conversation about NAD+ decline focused almost entirely on the supply side: NAMPT expression falls, dietary precursor intake decreases, and the body simply makes less NAD+. That framing is correct but incomplete. The 2016 paper by Camacho-Pereira and colleagues from Eduardo Chini’s group at the Mayo Clinic reframed the issue substantially. In that study, mice genetically lacking CD38 maintained NAD+ levels comparable to young animals even as they aged. Their SIRT1 and SIRT3 activity stayed elevated, their mitochondrial function remained healthier, and their metabolic parameters looked significantly better than age-matched controls with normal CD38. The implication: CD38 upregulation with age isn’t a minor contributing factor. It’s a primary driver of the NAD+ collapse that underpins much of what we call cellular ageing.

Why ageing drives CD38 expression higher

The connection between ageing and CD38 runs through inflammaging, the chronic, low-grade systemic inflammation that accumulates across decades. Activated macrophages and natural killer cells express very high levels of CD38. As you age, two processes feed each other: senescent cells accumulate and release a pro-inflammatory secretory cocktail (the senescence-associated secretory phenotype, or SASP), which recruits immune cells; those immune cells express more CD38, which depletes more NAD+; falling NAD+ then impairs the sirtuin and PARP-mediated pathways that normally help clear senescent cells. You end up with a self-reinforcing cycle where more inflammation produces more CD38, which produces less NAD+, which reduces the cellular defences against further senescence and inflammation.

This loop partly explains why NAD+ decline tends to steepen in midlife rather than fall smoothly from early adulthood. It’s roughly when senescent cell burden and systemic inflammation reach a threshold where they start amplifying each other.

A second mechanism involves DNA damage. As genomic instability increases with age, PARP enzymes are activated for repair and consume NAD+ in large quantities. At the same time, DNA damage responses can induce CD38 expression. The result is elevated demand for NAD+ colliding with elevated catabolism, a combination that makes it difficult to maintain NAD+ levels through precursor supplementation alone, particularly at modest doses.

Apigenin as a CD38 inhibitor: mechanism and evidence

Apigenin is a flavone, a subclass of flavonoids, found naturally in chamomile, parsley, celery, and several other plants. Its relevance to NAD+ biology came into focus when researchers identified it as a potent non-competitive inhibitor of CD38’s glycohydrolase activity. The 2013 study by Escande and colleagues characterised this effect clearly: apigenin suppressed CD38 NADase activity, reduced cADPR production, and raised intracellular NAD+ levels in treated cells. Animal studies building on this work showed that apigenin supplementation improved NAD+-dependent metabolic parameters, including insulin sensitivity and mitochondrial function, via increased sirtuin activity downstream of higher NAD+.

What changes when CD38 is inhibited

When CD38 activity falls, NAD+ that would otherwise be catabolised becomes available for the enzymes that use it productively. The most important beneficiaries are sirtuins, particularly SIRT1 and SIRT3, which regulate mitochondrial biogenesis, fatty acid oxidation, autophagy, and DNA repair. PARP enzymes that maintain genomic stability also benefit from improved substrate availability. And the salvage pathway operates more efficiently when it isn’t fighting constant CD38-mediated depletion.

This is the mechanistic case for combining apigenin with an NMN supplement: NMN opens the biosynthetic tap, apigenin partially closes the CD38 drain, and the combined effect on intracellular NAD+ can exceed what either intervention achieves alone. Animal data support this synergy. Direct human evidence comparing NMN alone versus NMN with CD38 inhibition is not yet available, so this remains mechanistically well-grounded extrapolation rather than confirmed human outcome data.

Where the evidence currently stands

No published randomised controlled trial has measured blood or intracellular NAD+ before and after apigenin supplementation as a primary endpoint in humans. The mechanistic foundation is well established, the animal data are consistent, and the dose-response relationship in preclinical models is reasonably clear. Doses in the range of 25 to 100 mg appear effective at inhibiting CD38 in animal models. This doesn’t mean the human evidence is absent; it means the clinical trial infrastructure around apigenin specifically hasn’t caught up with the mechanistic work. Anyone claiming apigenin is a proven human NAD+ booster with a specific percentage improvement is running ahead of the data. Anyone dismissing it because human trials are sparse is ignoring a body of well-characterised mechanistic evidence.

Dietary sources versus supplemental apigenin

Chamomile tea is one of the richest dietary sources of apigenin, with high-quality dried chamomile delivering meaningful amounts per cup. Fresh parsley is another significant source, as are celery, dried oregano, and certain citrus varieties. The practical challenge with dietary intake is consistency: apigenin content in food varies considerably based on cultivation conditions, soil composition, processing, and storage. Two cups of chamomile tea can deliver very different amounts depending on the product and preparation.

Supplemental apigenin removes that variability and delivers a defined dose. The AVEA Booster includes 50 mg of apigenin alongside resveratrol (Veri-te™ trans-resveratrol 150 mg), ubiquinol (CoQ10, 100 mg), pterostilbene (50 mg), betaine (50 mg), and nicotinamide (16 mg). The formulation rationale is that an NAD+ strategy requires multiple simultaneous interventions: production support through NMN or the nicotinamide in the Booster, consumption management through CD38 inhibition, sirtuin activation through resveratrol and pterostilbene, and mitochondrial efficiency through CoQ10.

Practical guidance: dosing, timing, and cautions

At the supplemental doses studied in preclinical models, apigenin is generally well tolerated. Doses below 25 mg are unlikely to provide meaningful CD38 inhibition based on animal data. Doses above 150 mg don’t appear to add proportional benefit and increase the likelihood of drug interactions. The 50 to 100 mg range represents the mechanistically motivated target.

One practical consideration worth knowing: apigenin is a moderate inhibitor of cytochrome P450 enzymes, particularly CYP1A2 and CYP2C9. If you take medications metabolised by these pathways (certain anticoagulants, some antidiabetic agents, several psychiatric medications), discuss apigenin supplementation with your prescribing physician before starting. This affects a minority of supplement users, but it’s a real pharmacokinetic interaction, not a theoretical one.

Higher doses (above 50 mg) can have mild sedative effects via GABA receptor interactions, the same mechanism behind chamomile tea’s reputation for relaxation. This isn’t a problem for most people. Taking apigenin in the evening, if you’re on a split NMN protocol with an evening dose, means any calming effect is simply irrelevant. Morning use works equally well if that’s your preference. There’s no published evidence that timing apigenin relative to NMN within the same day meaningfully changes NAD+ outcomes.

Where to go next

CD38 inhibition addresses the catabolism side of the NAD+ equation. To complete the picture, the companion article “Methylation, betaine, and TMG in NAD+ recycling” covers a frequently overlooked bottleneck: when you supplement NMN heavily, downstream methylation demand can limit how efficiently the precursor translates into usable NAD+. Betaine, also present in the AVEA Booster, addresses this directly.

For context on how CD38 and NAD+ fit into the wider biology of cellular ageing, “The 12 hallmarks of ageing explained” provides the framework in which all of these mechanisms operate. And if you want to understand what higher NAD+ levels activate downstream, specifically sirtuin biology and its real triggers, “Sirtuin activation: what really triggers it” gives a clear-eyed view of what the evidence supports and what remains contested.