Most discussions of NAD+ decline focus on the supply side: as we age, the enzymes that synthesize NAD+ become less active, dietary precursor availability may decrease, and the demand from DNA repair and other NAD+-consuming processes increases. All of this is true. But a major and often underemphasized driver of age-related NAD+ depletion operates on the degradation side: an enzyme called CD38 that consumes NAD+ at extraordinary rates and whose expression increases dramatically with age.
Understanding CD38 is important for anyone serious about NAD+ supplementation — not just as a piece of biochemistry, but because it explains why supplementation alone may have limits, why certain lifestyle choices matter mechanistically, and why a small number of natural compounds that inhibit CD38 have attracted research interest as longevity interventions.
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What CD38 Is and What It Does
CD38 is a multifunctional enzyme — formally an NAD+ glycohydrolase and ADP-ribose cyclase — expressed on the surface and interior of many cell types, with particularly high expression in immune cells, cardiac tissue, and the brain. Its primary biochemical activity is the degradation of NAD+ into ADP-ribose (ADPR) and nicotinamide, or into cyclic ADPR (cADPR) and nicotinamide depending on the reaction conditions. Both products are signaling molecules — cADPR in particular is an important second messenger in calcium signaling — but the net metabolic effect of CD38 activity is the consumption of NAD+.
CD38 is remarkably efficient at this consumption. Research has established that CD38 has a relatively low affinity for NAD+ but very high catalytic activity, and critically, it consumes far more NAD+ than it needs to produce the cADPR and ADPR signaling products that are its biological purpose. For every molecule of NAD+ turned into a functionally useful product, CD38 degrades many more to nicotinamide and ADPR that are not retained in active signaling pathways. This catalytic inefficiency makes CD38 a significant drain on the cellular NAD+ pool — consuming substrate in excess of what its signaling functions require.
In young, healthy organisms, CD38 activity is kept in balance by the rate of NAD+ biosynthesis through the salvage pathway and other routes. The problem emerges with aging, when CD38 expression increases substantially while NAD+ biosynthesis capacity declines.
Why CD38 Increases with Age
The primary driver of CD38 upregulation with aging is inflammation. CD38 expression in immune cells — particularly macrophages — is strongly induced by pro-inflammatory cytokines including TNF-alpha, IL-1β, and interferon-gamma. As chronic low-grade inflammation (inflammaging) increases with age, and as senescent cells accumulate and secrete their SASP-driven cytokine profiles, CD38 expression in tissue-resident macrophages and other immune cells rises in proportion to the inflammatory burden.
This creates one of the most pernicious cycles in aging biology: inflammation induces CD38, CD38 depletes NAD+, reduced NAD+ impairs SIRT1 activity, reduced SIRT1 activity allows NF-κB to operate less restrained, NF-κB drives more pro-inflammatory gene expression, which further increases CD38 expression. The cycle is self-reinforcing and becomes more entrenched with advancing age.
The foundational research establishing CD38 as the primary driver of age-related NAD+ decline was published by Camacho-Pereira et al. (2016) in Cell Metabolism. This study demonstrated that CD38 knockout mice — lacking the CD38 gene entirely — maintained substantially higher NAD+ levels with aging compared to wild-type mice, and showed improved metabolic function, increased sirtuin activity, and protection against the NAD+ decline normally observed with aging. The paper also demonstrated that CD38 expression in adipose tissue macrophages increased dramatically with age and obesity in both mice and humans — connecting the CD38 mechanism to metabolic aging and identifying the specific cellular source of much of the increased CD38 activity.
A subsequent study by Covarrubias et al. (2020) in Nature Metabolism extended this picture by showing that senescence-associated macrophages in aged adipose tissue were the primary source of CD38 upregulation — directly linking senescent cell accumulation (covered in the article on senescent cells and senolytics) to CD38-mediated NAD+ depletion. This finding has important implications: clearing senescent cells through senolytics should reduce the CD38-expressing macrophage population they attract, thereby reducing the NAD+ drain from CD38 — an indirect but mechanistically coherent benefit of senolytic protocols.
The Scale of CD38’s Impact
The quantitative importance of CD38 in age-related NAD+ decline is substantial. Camacho-Pereira et al. found that CD38 knockout mice at middle age had NAD+ levels in liver and other tissues comparable to young wild-type animals — meaning that CD38 alone was responsible for the majority of the observed NAD+ decline in the wild-type animals. This is a striking finding: not mitochondrial dysfunction, not declining NAMPT expression, not increasing PARP demand, but a single NAD+-degrading enzyme was the dominant driver of NAD+ decline in these mice.
Whether the same quantitative primacy applies in humans has not been directly established with equivalent rigor, but the conserved biology — CD38 expression increases with age and inflammation in human tissues, including in the same adipose tissue macrophage populations — is consistent with a major role. The NAD+ decline in aging is multifactorial, but CD38 appears to be the largest single contributor rather than one among many roughly equal factors.
This matters for supplementation strategy: if the primary problem is not insufficient NAD+ synthesis but excessive NAD+ degradation, then simply adding more precursor (NMN or NR) is addressing the supply side of an equation with a large demand-side problem. Supplementation can compensate for the CD38-mediated drain, but it is operating against ongoing enzymatic degradation rather than in a system where the synthesis-degradation balance is near-normal. This does not undermine the case for supplementation — it explains why higher doses may be needed in older, more inflamed individuals, and why reducing CD38 activity would be a valuable complementary strategy.
Natural CD38 Inhibitors: What the Research Shows
Several natural compounds have demonstrated CD38-inhibitory activity in laboratory and animal studies. None has established clinical evidence for CD38 inhibition in humans, but the preclinical findings are specific enough and the compounds accessible enough that they have attracted attention in longevity supplement circles.
Apigenin
Apigenin — a flavonoid found in parsley, chamomile, celery, and other plants — is the most studied natural CD38 inhibitor in this context. Escande et al. (2013) in Diabetes demonstrated that apigenin inhibited CD38 activity in vitro and raised NAD+ levels in mice, producing metabolic improvements including reduced obesity and improved glucose tolerance that paralleled the effects of CD38 knockout. This was a mechanistically clean demonstration of the concept: a natural compound, by inhibiting CD38, could raise NAD+ levels and produce functional metabolic benefits in a living mammalian system.
Apigenin’s potency as a CD38 inhibitor in these studies was meaningful — it inhibited CD38 at concentrations achievable through supplementation in mice. Whether equivalent tissue concentrations are achieved in humans through typical supplemental doses has not been directly confirmed with human pharmacokinetic data, and no human trial has demonstrated that apigenin raises NAD+ levels or inhibits CD38 activity in human tissues.
Quercetin and Luteolin
Quercetin — already discussed extensively for its senolytic and anti-inflammatory properties in the article on quercetin: complete guide — also has CD38-inhibitory activity in vitro. Luteolin, a structural relative of apigenin found in many of the same plant sources, similarly inhibits CD38. The overlapping activities of these flavonoids — senolytic, anti-inflammatory, and potentially CD38-inhibitory — make them interesting as multi-mechanism compounds rather than single-pathway supplements, though the CD38 inhibition component is less well-established in human contexts than their other activities.
Kuromanin and Cyanidin Compounds
Certain anthocyanins — the pigments responsible for the blue and red colors of blueberries, blackberries, and similar fruits — have shown CD38-inhibitory activity in laboratory studies. Kuromanin (cyanidin-3-glucoside) is among the more potent in this group. These compounds are present in meaningful amounts in the foods that contain them, and there is a reasonable dietary argument for including anthocyanin-rich foods in a diet aimed at supporting NAD+ levels — though the specific mechanism via CD38 inhibition in humans remains to be confirmed.
Anti-Inflammatory Strategies as CD38 Management
Because CD38 upregulation is primarily driven by inflammation, any intervention that reduces chronic inflammation also indirectly reduces CD38-mediated NAD+ drain. This is one of the most practically actionable insights from the CD38 biology: the longevity interventions that address inflammaging are not just broadly beneficial for health — they specifically protect the NAD+ pool by reducing the inflammatory signal that drives CD38 expression.
Exercise reduces systemic inflammatory markers including CRP, IL-6, and TNF-alpha. Dietary patterns that reduce refined carbohydrate and processed food intake reduce inflammatory signaling. Adequate sleep reduces the inflammatory burden from sleep-deprivation-induced cytokine elevation. Senolytics reduce the SASP-driven inflammatory load from accumulated senescent cells. Each of these reduces the CD38 expression that is their downstream consequence, helping to preserve the NAD+ pool more effectively than supplementation alone can achieve.
The most mechanistically targeted lifestyle intervention for CD38 is senolytic use: directly clearing the senescent cells that attract CD38-expressing macrophages removes the primary source of the inflammatory drive to CD38 expression in aged adipose tissue. The combination of senolytic protocols (fisetin + quercetin) and NAD+ precursor supplementation therefore addresses two complementary aspects of the same problem — reducing the rate of NAD+ degradation while increasing the rate of NAD+ synthesis.
Pharmaceutical CD38 Inhibitors
Daratumumab — a monoclonal antibody targeting CD38, approved for multiple myeloma treatment — is the most potent CD38 inhibitor currently in clinical use. Its application in longevity contexts is theoretical and speculative; it is an intravenous oncology drug with significant side effects and not a candidate for healthy aging use. It is mentioned here to illustrate that CD38 inhibition has been pharmacologically validated as an achievable therapeutic target in humans, and to provide context for the interest in natural CD38 inhibitors as less potent but more accessible alternatives.
Several pharmaceutical-grade small molecule CD38 inhibitors are in preclinical and early clinical development for metabolic disease indications — not longevity specifically, but the metabolic overlap is substantial. This research pipeline suggests that more targeted CD38 inhibition may become clinically available in the next decade, which would represent a significant addition to the NAD+ restoration toolkit beyond precursor supplementation.
Integrating CD38 Understanding into a Longevity Protocol
The CD38 picture has several practical implications for longevity supplement and lifestyle protocol design.
First, it explains why NAD+ precursor doses tend to need to be higher in older, more inflamed individuals — they are supplementing against a larger ongoing degradation drain, not just a biosynthesis deficit. The age-adjusted dosing guidance in the NMN dosage guide is mechanistically consistent with this: older adults with more CD38 activity need more NAD+ input to achieve equivalent NAD+ elevation.
Second, it provides a specific mechanistic rationale for anti-inflammatory lifestyle practices as NAD+ support strategies — not just because reducing inflammation is generally good, but because inflammation directly drives the enzyme responsible for much of the NAD+ decline in aging.
Third, it connects the senolytic rationale to NAD+ biology in a specific and testable way: clearing senescent cells reduces the macrophage population they attract, reduces local and systemic CD38 expression, and thereby reduces NAD+ degradation rate. This means senolytic protocols and NAD+ precursor supplementation are not just complementary in a general sense — they address the same pathological cycle from different angles.
Fourth, it suggests that including apigenin — readily available as a supplement derived from parsley or chamomile extract — alongside NMN or NR may provide a modest additional NAD+ conservation benefit through CD38 inhibition, though this combination has not been studied in humans and the evidence for apigenin’s CD38 inhibitory effect in human tissues is preclinical.
Frequently Asked Questions
If CD38 is the main driver of NAD+ decline, why not just inhibit CD38 instead of supplementing NMN?
In principle, both strategies address the same problem — low cellular NAD+ — from different directions. Inhibiting CD38 reduces the rate of NAD+ degradation; supplementing NMN increases the rate of NAD+ synthesis. The practical limitation of CD38 inhibition as a primary strategy is that no accessible, well-evidenced CD38 inhibitor for humans currently exists. Apigenin and quercetin have preclinical evidence but lack human pharmacokinetic confirmation of meaningful CD38 inhibition. NMN and NR, by contrast, have multiple human trials demonstrating NAD+ elevation and functional effects. The evidence-based approach is to use proven NAD+ precursors as the primary intervention and consider natural CD38 inhibitors as potential complementary additions — not as substitutes for supplementation.
Does reducing inflammation actually raise NAD+ levels?
The mechanistic prediction is yes — reducing the inflammatory signals that drive CD38 expression should reduce CD38 activity and slow NAD+ degradation. Direct evidence in humans showing that inflammation reduction raises NAD+ levels through CD38 reduction specifically is limited; the mechanistic chain is well-established at the molecular level but has not been studied with the kind of controlled human intervention trial that would directly confirm it. The relationship between metabolic health, inflammation, and NAD+ levels is consistent with this mechanism across observational data, but the specific causal pathway via CD38 has not been isolated in human clinical experiments.
Should I take apigenin alongside my NMN supplement?
Apigenin is safe at typical supplemental doses — it is a widely consumed flavonoid with no identified safety concerns at the amounts available in supplements. The preclinical evidence for its CD38 inhibitory activity and NAD+-raising effect in mice is genuine. The gap is human evidence: no clinical trial has confirmed that supplemental apigenin raises NAD+ levels in humans through CD38 inhibition. Adding apigenin at 50–100 mg/day is a low-risk addition with mechanistic rationale, but it should be understood as a preclinical-supported hypothesis rather than an established human effect. Anyone interested in exploring this addition should weigh the preclinical evidence alongside their overall supplement budget and the stronger-evidence interventions that deserve priority.
Is CD38 the same enzyme targeted by daratumumab in cancer treatment?
Yes — daratumumab is a monoclonal antibody that binds to CD38 on the surface of myeloma cells, triggering immune-mediated destruction of those cells. Multiple myeloma cells express very high levels of CD38, making it an effective therapeutic target. The CD38 being targeted in myeloma treatment is the same molecule whose age-related upregulation drives NAD+ depletion in normal aging, but the therapeutic context and mechanism of action are entirely different: in myeloma, the goal is to use CD38 as a surface marker to kill cancer cells; in aging biology, the goal is to inhibit CD38’s enzymatic activity to preserve NAD+. The molecule is the same; the interventional strategy is unrelated.