Why NAD+ Supplements Are a Waste of Money

Your NAD+ levels are declining with age. That much is true. But the reason almost everyone believes is wrong, and the reason matters because it completely changes what you should actually do about it.

The common belief is that your body simply produces less NAD+ as you get older, the way an aging factory produces fewer parts. And if that were true, then flooding the system with precursors like NMN or NR would make perfect sense. You would just be replacing what the factory stopped making. The problem is that the factory is not the issue.

To understand what is actually happening, you need the full picture first.

Your body runs a continuous recycling loop for NAD+, which is a molecule your cells use as fuel for hundreds of enzymatic reactions, particularly the ones involved in energy production and DNA repair. When that fuel gets used, your body breaks it down and rebuilds it through a pathway controlled by an enzyme called NAMPT, short for nicotinamide phosphoribosyltransferase, which is essentially the machine that turns the raw materials back into usable NAD+. When this system is healthy and the recycling rate keeps up with demand, your NAD+ stays stable. When demand outpaces recycling, levels drop.

That gap between demand and recycling is exactly what aging creates.

Here is how it starts. As your cells accumulate damage over time, some of them reach a point where they stop dividing but also refuse to die. These are called senescent cells, and they sit in your tissues releasing a constant stream of inflammatory signals. Those signals are your immune system's alarm, and your immune system responds the way it always does to alarms: it mobilizes.

The response involves activating macrophages, which are immune cells, and those macrophages dramatically upregulate an enzyme called CD38, which produces the signaling molecules the immune response requires. The fuel CD38 runs on is NAD+.

A 2020 study published in Nature Metabolism traced this exact chain. Senescent cells secrete inflammatory cytokines, those cytokines cause nearby macrophages to increase their CD38 expression by up to 600-fold, and that spike in CD38 activity consumes NAD+ faster than the recycling loop can replace it. The senescent cells are not just causing inflammation. They are indirectly draining your cellular fuel.

A separate study published in Cell Metabolism confirmed the downstream result. CD38 activity increases two to three fold across all tissues as you age, and that increase tracks almost perfectly with the decline in NAD+ levels. When researchers genetically eliminated CD38 in mice, NAD+ stayed constant at every age. The mice aged, but their NAD+ did not drop.

That one finding is worth sitting with. The problem is not production. Something is consuming it.

Damaged mitochondria make this worse through a second drain. When mitochondria take on damage, they activate a class of repair enzymes called PARPs, and PARPs also use NAD+ as their fuel source. So you have two separate consumers pulling from the same pool at the same time: the CD38 driven by senescent cell inflammation, and the PARPs driven by mitochondrial damage.

This is the bathtub with two open drains. Pouring in more water, which is what NMN and NR supplements do, does not help you if you never close them. And there is a second problem with those supplements that the industry does not advertise.

Research published in FEBS Letters found that gut bacteria intercept NMN before it can be absorbed, converting it through a process called deamidation into nicotinic acid, which is plain niacin. A study in Science Advances confirmed the same thing for both NMN and NR: most oral precursors become niacin before they ever reach your bloodstream. When researchers wiped out the gut microbiome in that FEBS study using antibiotics, direct NMN uptake went up, which confirmed that the conversion is happening in the gut specifically. You are largely paying premium prices for something your body converts into a vitamin that costs pennies.

A review published in Science Advances looked at 25 human studies on NR supplementation and concluded there is what the authors called an unfortunate tendency in the literature to exaggerate the importance and robustness of the reported effects. The data on human benefit is thin, and what benefit exists is probably attributable to niacin anyway.

So if the problem is consumption, the solution is reducing what is doing the consuming.

Exercise is the most accessible intervention. A systematic review and meta-analysis published in Frontiers in Public Health found that regular exercise training increases NAMPT expression by over 127%, with a large effect size. That is not a marginal improvement. That is more than doubling the capacity of the enzyme responsible for recycling NAD+. Exercise does not just burn energy, it upgrades the machinery that replenishes it.

For the mitochondrial drain, a peptide called SS-31 works by targeting a molecule called cardiolipin inside the mitochondrial membrane, stabilizing the structure that generates energy and reducing the damage that triggers PARP activation in the first place. A study published in Aging Cell found that neither SS-31 nor NMN alone significantly raised NAD levels in aged mouse hearts, but the combination did, and it best recapitulated the metabolic profile of young hearts. That result tells you something important: you get the benefit when you fix the mitochondria first, and then support the precursor pool.

For the senescent cell drain, a peptide called FOXO4-DRI works by disrupting the survival signal that keeps senescent cells alive when they should have cleared out. Fewer senescent cells means less inflammatory signaling, which means less CD38 activation, which means less NAD+ being consumed by the immune response.

Once you close the drains, the recycling loop can actually keep up. And at that point, if you want precursor support on top of that, niacin does the same thing the expensive supplements do.

The entire supplement industry built around NAD+ precursors is selling you a solution to the wrong problem. They identified a real decline, correctly identified that NAD+ is involved, and then stopped asking why. The decline is not a shortage. It is a symptom of a system under load. And you cannot fix a system under load by adding more fuel.

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References

1. Camacho-Pereira J, Tarrago MG, Chini CCS, et al. CD38 Dictates Age-Related NAD Decline and Mitochondrial Dysfunction through an SIRT3-Dependent Mechanism. Cell Metabolism. 2016;236:1127-1139. Finding: CD38 activity increases 2-3 fold with age across all tissues, with near-perfect inverse correlation to NAD+ levels. CD38 knockout mice maintained NAD+ at all ages. Source
2. Covarrubias AJ, Kale A, Perrone R, et al. Senescent cells promote tissue NAD+ decline during ageing via the activation of CD38+ macrophages. Nature Metabolism. 2020;211:1265-1283. Finding: Senescent cells secrete inflammatory cytokines that cause macrophages to upregulate CD38 expression up to 600-fold, establishing the causal chain from cellular senescence to NAD+ decline. Source
3. Kim LJ, Chalmers TJ, Madawala R, et al. Host-microbiome interactions in nicotinamide mononucleotide NMN deamidation. FEBS Letters. 2023;59717:2196-2207. Finding: Gut bacteria deamidate NMN before absorption, converting it to nicotinic acid niacin. Ablation of microbiome with antibiotics increased direct NMN uptake, confirming gut conversion. Source
4. Science Advances enterohepatic circulation study. Finding: NMN and NR facilitate NAD+ synthesis primarily through conversion to niacin-pathway metabolites in the gut, confirming that most oral precursors become niacin before absorption. Source
5. Sun X, Su L, Bu T, Zhang Y. Exercise training upregulates intracellular nicotinamide phosphoribosyltransferase expression in humans: a systematic review with meta-analysis. Frontiers in Public Health. 2023;11:1287421. Finding: Exercise training increases NAMPT expression by over 127% with a large effect size Cohen's d = 0.81. Source
6. Whitson JA, Martin SS, Zhang H, et al. SS-31 and NMN: Two paths to improve metabolism and function in aged hearts. Aging Cell. 2020;1910:e13213. Finding: Neither SS-31 nor NMN alone significantly increased resting NADH levels in aged mouse hearts. Only the combination did, best recapitulating the young state. Source
7. Brakedal B, Doring A, Riber C, et al. What is really known about the effects of nicotinamide riboside supplementation in humans. Science Advances. 2023;929:eadi4862. Finding: Review of 25 NR human studies concluded there is "an unfortunate tendency in the literature to exaggerate" the importance and robustness of reported effects. Source

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