Why NAD+ Supplements Are a Waste of Money

Your cells are not running low on NAD+ because they forgot how to make it. They are running low because something is burning through it faster than your body can replace it, and that is a completely different problem than the supplement industry wants you to think you have.

To understand why that matters, you need the full picture first.

NAD+ is something called a coenzyme, which is a molecule that enzymes need as a partner to do their job. Your mitochondria use it to convert food into usable energy. Your DNA repair systems use it as fuel when they find damage. Your sirtuins, which are proteins that regulate aging at the cellular level, use it to control gene expression. The entire system depends on NAD+ being available, and as you age, less of it is available. That part is true and well documented. Where the story goes wrong is in the explanation of why.

The common belief is that aging cells simply produce less NAD+. That belief is not entirely wrong. Production does slow somewhat. But production is not the main driver of the decline, and that distinction changes everything about how you should respond to it.

There is an enzyme called CD38, which is a protein your immune cells use to generate signaling molecules during an inflammatory response. The problem is that CD38 uses NAD+ as its raw material, and it does not use it efficiently. For every molecule of NAD+ that CD38 processes, it produces only trace amounts of the signaling molecules your immune system actually needs. Most of the NAD+ is simply consumed in the process. Research published in Cell Metabolism found that CD38 activity increases two to three fold across all tissues as you age, and the correlation with NAD+ levels is nearly perfect. When researchers eliminated CD38 entirely in mice, NAD+ levels stayed constant at every age. The aging animals had the same NAD+ as young ones. Not because they made more, but because nothing was burning through it.

So why does CD38 activity increase so much with age in the first place?

This is where senescent cells enter the picture. Senescent cells are cells that have stopped dividing but have not been cleared out of the body the way they are supposed to be. They accumulate over time, and they are not quiet. They continuously secrete inflammatory signals, which recruits your immune system to the area. That immune response upregulates CD38. A 2020 study in Nature Metabolism traced this chain directly and found that senescent cells cause macrophages, which are a type of immune cell, to increase their CD38 expression by up to 600 fold. The more senescent cells accumulate, the louder the alarm signal, the more NAD+ the immune response consumes.

And then there is a second drain running in parallel.

Damaged mitochondria activate enzymes called PARPs, which stands for poly ADP-ribose polymerases. PARPs are your cell's emergency DNA repair crew, and they also use NAD+ as their primary fuel. When mitochondria are structurally compromised, they leak electrons and generate what is called oxidative stress, which is chemical damage to surrounding molecules including DNA. That damage triggers PARP activity, which burns NAD+, which impairs the mitochondria further, which generates more oxidative stress. The cycle feeds itself.

This is why pouring in more NAD+ precursors through supplements does not solve the problem. If the drain is open, the tub does not fill. And on top of that, a 2023 study in FEBS Letters found that gut bacteria convert NMN, one of the most marketed NAD+ precursors, into niacin before it even reaches your bloodstream. A separate study in Science Advances confirmed that most oral precursors end up going through the niacin pathway regardless of which precursor you started with. A review of 25 human NR studies published in Science Advances concluded that the literature has "an unfortunate tendency to exaggerate" the importance and robustness of the reported effects. You are largely paying a large premium for something that becomes plain niacin in your gut anyway.

So if the problem is consumption driven by senescent cells and damaged mitochondria, the actual leverage points are those two things.

Exercise is the most accessible intervention because it increases something called NAMPT, which is the enzyme responsible for recycling NAD+ through what is known as the salvage pathway. A 2023 systematic review and meta-analysis found that exercise training increases NAMPT expression by over 127 percent, with a large effect size. That means your body is not just getting more NAD+ from exercise, it is getting better at recovering and reusing what it already has.

For the mitochondrial drain, a compound called SS-31 is worth understanding. SS-31 is a peptide that targets the inner mitochondrial membrane specifically and helps restore structural integrity there. Damaged mitochondria have a distorted inner membrane that disrupts the proteins responsible for energy production, and SS-31 addresses that directly rather than trying to flood the system with more substrate. A 2020 study in Aging Cell found that neither SS-31 nor NMN alone significantly raised resting NAD levels in aged mouse hearts, but the combination of the two did, and it most closely recapitulated what the young heart looked like.

For the senescent cell problem, a peptide called FOXO4-DRI has shown early promise in animal models as what is called a senolytic, which is a compound that selectively clears senescent cells rather than just suppressing their signals. The human evidence is still limited and this is an area where the science is actively developing, but the mechanism is sound: if the senescent cells driving the CD38 upregulation are removed, the inflammatory signal drops, CD38 activity drops, and NAD+ consumption drops.

If you want precursor support after addressing those upstream problems, niacin works and costs almost nothing. Your gut converts the expensive precursors into it anyway.

The deeper point here is not that NAD+ does not matter. It matters enormously. The point is that your body is not a depleted tank, it is a system with a drain left open, and no amount of refilling fixes a drain. Understanding where the drain is and why it opened is the only way to actually close it.

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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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