Why NAD+ Supplements Are a Waste of Money

Your NAD+ levels are dropping as you age, and the supplement industry has a simple story about why: your body is making less, so take more. That story is wrong, and the research that disproves it has been available for years.

To understand what's actually happening, you need the full chain first.

Your body produces NAD+, something called nicotinamide adenine dinucleotide, which is a molecule your cells use as fuel for repair, energy production, and signaling. Levels of this molecule decline as you age, and that decline is connected to basically every major marker of aging, from mitochondrial dysfunction to immune deterioration. The supplement industry's response was to sell you precursor molecules, things like NMN and NR, that your body can theoretically use to build more NAD+. Billions of dollars later, the evidence that this actually works in humans is thin enough that a 2023 review of 25 human NR studies concluded there is an unfortunate tendency in the literature to exaggerate the importance and robustness of reported effects.

The reason the approach fails is that the problem was never supply. It was consumption.

Here is what's actually happening in your body as you age. Your cells accumulate damage over time, and some of those damaged cells reach a state called senescence, which means they stop dividing but don't die the way they're supposed to. Senescent cells aren't inert. They secrete a constant stream of inflammatory signals, and those signals recruit immune cells called macrophages to the area. Here is where it gets specific: that inflammatory environment causes those macrophages to dramatically upregulate an enzyme called CD38, which is an enzyme that uses NAD+ as a raw material to produce the signaling molecules the immune system needs to respond to all that damage.

Research published in Nature Metabolism found that this upregulation is not subtle. Macrophages in a senescent environment increase their CD38 expression by up to 600-fold. The immune system is not mildly inconvenienced. It is burning through NAD+ at an enormous rate trying to respond to a problem that never resolves because the senescent cells are still there producing the same inflammatory signals tomorrow that they produced today.

A separate study published in Cell Metabolism filled in the scale of the problem. CD38 activity increases two to three fold across all tissues as you age, and the correlation between CD38 activity and NAD+ decline is nearly perfect in both directions. When researchers eliminated CD38 in mice entirely, NAD+ levels stayed constant at every age. The mice got older but their NAD+ didn't drop. That finding is the clearest possible evidence that the decline isn't about your body producing less. It's about one specific enzyme consuming more.

And then there's a second drain running simultaneously.

Damaged mitochondria, which accumulate for many of the same reasons senescent cells do, activate a class of repair enzymes called PARPs, which stands for poly ADP-ribose polymerases. PARPs use NAD+ as their fuel source to attempt mitochondrial repair. So while CD38 is burning NAD+ trying to manage the inflammatory fallout from senescent cells, PARPs are burning NAD+ trying to fix mitochondria that keep getting damaged. Both drains are open at the same time.

Pouring more NMN into that system is like pouring water into a bathtub while the drain is fully open. The water level doesn't rise because the problem was never the faucet. And there's an additional problem with oral NMN specifically: gut bacteria convert most of it into nicotinic acid, which is plain niacin, before it's ever absorbed. Research published in FEBS Letters confirmed this directly, finding that ablating the microbiome with antibiotics was what allowed direct NMN uptake to occur, meaning a normal gut microbiome converts the supplement into something far cheaper before your body ever sees it.

So if the problem is consumption, the solution has to address what's doing the consuming.

The first and most accessible intervention is exercise, done consistently. A systematic review and meta-analysis published in Frontiers in Public Health found that exercise training increases expression of something called NAMPT, which is nicotinamide phosphoribosyltransferase, the enzyme your body uses to recycle NAD+ rather than synthesize it from scratch. The increase across studies was over 127%, with a large effect size. Exercise doesn't just burn calories. It actively upregulates the recycling machinery your body uses to maintain NAD+ levels, and it does this through a mechanism that doesn't depend on how much CD38 is running.

The second intervention targets the mitochondrial damage that's fueling the PARP drain. A peptide called SS-31 works by anchoring to a specific lipid in the inner mitochondrial membrane called cardiolipin, which stabilizes the proteins responsible for electron transport and ATP production. When mitochondria are structurally stabilized, the repair signal that activates PARPs becomes less intense, which means less NAD+ burned on repair attempts. Research published in Aging Cell found that neither SS-31 nor NMN alone significantly raised resting NAD+ levels in aged mouse hearts, but the combination did, and did so in a way that best matched the young baseline. That finding suggests that fixing the structural damage first is what allows precursor support to actually do something.

The third intervention targets the upstream cause directly: the senescent cells that are driving CD38 activity in the first place. A peptide called FOXO4-DRI works by interfering with the survival signal that keeps senescent cells alive when they should have cleared. When those cells are removed, the inflammatory signal drops, the macrophages stop upregulating CD38, and the drain slows. Addressing senescence doesn't just help NAD+. It addresses a root cause of the signaling environment that makes aging accelerate across multiple systems.

Once those drains are reduced, if you still want precursor support, niacin costs pennies and your gut converts most NMN into it anyway.

The real insight here is not that NAD+ supplementation is useless. It's that supplementation without addressing consumption is treating a symptom of a symptom. The senescent cells drive the inflammation that drives CD38 that drives the NAD+ decline that drives the mitochondrial dysfunction. Buying NMN and skipping that chain means you're paying a significant premium to temporarily address the fourth link in a four-link chain while the first three keep running.

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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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