Why NAD+ Supplements Are a Waste of Money

Your body isn't running low on NAD+ because it stopped making enough. It's running low because something is consuming it faster than your cells can replace it, and the supplement industry has been selling you the wrong solution to that problem for years.

To understand why, you need the full picture first.

NAD+ is something called a coenzyme, which is a molecule your cells use as a fuel carrier to run hundreds of different processes, from energy production in your mitochondria to DNA repair to immune signaling. Young cells produce it, use it, and recycle it in a continuous loop. The problem is that as you age, that loop gets overwhelmed, and NAD+ levels drop significantly across most tissues. That drop has been linked to slower metabolism, worse cellular repair, and accelerated aging. The question nobody in the supplement industry wants to answer is: why does it drop?

The common explanation you'll hear is that your body simply makes less NAD+ as you get older, so you should take a precursor like NMN or NR to boost supply. That explanation is not entirely wrong. Precursor conversion does decline somewhat with age. But research published in Cell Metabolism found something that changes the whole picture. CD38, an enzyme your immune system uses to produce signaling molecules, increases two to three fold across all tissues as you age, and its activity shows a near-perfect inverse correlation with NAD+ levels. When researchers eliminated CD38 entirely in mice, NAD+ levels stayed constant at every age. The animals got older, but their NAD+ didn't fall.

That one finding reframes everything.

CD38 isn't just quietly present in your body. It is an aggressive consumer of NAD+, burning through it to generate the chemical signals your immune system needs to respond to damage and inflammation. And the reason it ramps up as you age traces directly back to something called senescent cells, which are damaged cells that have stopped dividing but haven't been cleared out of your tissues the way they should be. These cells are sometimes described as "zombie cells" because they don't die, they just sit there, and they send out a continuous stream of inflammatory signals called the senescence-associated secretory phenotype. Research published in Nature Metabolism found that those inflammatory signals cause immune cells called macrophages to upregulate CD38 expression by up to 600 fold. The more senescent cells accumulate, the louder that inflammatory signal gets, and the harder the immune system works to respond to it, burning through NAD+ the entire time.

So the chain runs like this: aging accumulates damaged cells, those cells signal inflammation, that inflammation drives CD38 activity up, and CD38 burns through NAD+ faster than your body can replace it.

Now add damaged mitochondria to that picture, because they make the problem worse. Mitochondria that are structurally compromised activate a class of repair enzymes called PARPs, which stands for poly ADP-ribose polymerases, and PARPs also use NAD+ as their fuel source. So you have two separate drain mechanisms running simultaneously: CD38 consuming NAD+ for immune signaling, and PARPs consuming it for mitochondrial repair. Pouring more precursor into that system is like pouring water into a bathtub with two open drains and wondering why it never fills.

This is exactly why a review of 25 human trials on nicotinamide riboside, published in Science Advances, concluded that there is an unfortunate tendency in the literature to exaggerate the importance and robustness of reported effects. And it's worth knowing that the gut further complicates NMN and NR supplementation, because research has shown that gut bacteria deamidate NMN before it can be absorbed, converting it into nicotinic acid, which is just niacin. A separate study confirmed that most oral NAD+ precursors are reaching the bloodstream through the niacin pathway anyway, meaning expensive NMN is functionally arriving as cheap niacin in most people.

If the problem is consumption, the fix has to address consumption.

The first lever is exercise, and the mechanism matters here. Exercise increases something called NAMPT, which is the enzyme responsible for recycling NAD+ from its broken-down components back into usable NAD+. A systematic review and meta-analysis found that exercise training increases NAMPT expression by over 127%, with a large effect size measured at a Cohen's d of 0.81. That is not a marginal improvement. That is the most powerful NAMPT intervention with the most evidence behind it, and it costs nothing.

The second lever is addressing mitochondrial damage directly. A compound called SS-31 is a mitochondria-targeted peptide that embeds itself in the inner mitochondrial membrane and reduces oxidative stress at the source. When you reduce the structural damage to mitochondria, you reduce PARP activation, which reduces one of the two major NAD+ drains. A study published in Aging Cell tested SS-31 and NMN separately in aged mouse hearts and found that neither alone significantly increased resting NAD levels. Only the combination produced meaningful recovery, which tells you that fixing the drain and adding supply together works in a way that supply alone never will.

The third lever is clearing the senescent cells that are driving the CD38 cascade to begin with. FOXO4-DRI is a peptide that disrupts a survival signal senescent cells use to avoid apoptosis, the normal cell death process, which causes those cells to die off rather than continuing to accumulate. Reducing the senescent cell burden reduces the inflammatory signaling that was driving macrophages to upregulate CD38, which reduces the primary NAD+ drain at its actual origin point.

Once those drains are addressed, if you still want precursor support, niacin is the honest answer. It is the form most oral precursors become anyway, it is effective at raising NAD+ in tissues, and it costs a fraction of NMN or NR.

The deeper point here is about what it means to treat a system versus treat a symptom. NAD+ decline is not a shortage problem that supplementation can solve. It is a demand problem created by biological damage that keeps accumulating and never gets cleared. Giving your cells more fuel while the damage that consumes it keeps compounding is not a longevity strategy. Fixing what is causing the consumption is.

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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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