Urolithin A and nicotinamide riboside (NR) have each attracted serious scientific attention as supplements that may support mitochondrial function and healthy aging. Both are positioned around the idea that declining mitochondrial quality underlies much of what we experience as aging—fatigue, muscle weakness, cognitive changes. But they work through entirely different biological pathways, and the evidence supporting them differs in meaningful ways.
This article compares the two compounds honestly: what they do mechanically, what human trials have actually found, where the evidence is stronger or weaker, and what remains genuinely unknown. Neither compound is a cure for aging, and neither should replace medical care. But understanding the distinction between them can help you ask better questions of your own doctor or registered dietitian.
Key Takeaways
- Urolithin A and NR support mitochondrial health through distinct mechanisms—mitophagy (quality control) versus NAD+ precursor replenishment (substrate supply).
- Urolithin A has human trial evidence showing improvements in muscle strength and exercise performance alongside mitochondrial biomarker changes [1].
- NR reliably raises NAD+ metabolite levels in blood and some tissues in humans, but functional muscle and performance benefits remain less consistently demonstrated [2].
- Both compounds appear generally safe in short-term human trials, but long-term safety and efficacy data are limited for both.
- These compounds address different parts of mitochondrial biology and are not direct substitutes for each other; neither is proven to prevent or treat any disease.
How Urolithin A Works: Clearing Out Damaged Mitochondria
Urolithin A is a compound produced in the gut when certain bacteria metabolize ellagitannins found in pomegranates, walnuts, and some berries. Not everyone produces it efficiently—gut microbiome composition varies considerably between individuals, which is one reason supplemental forms have been developed.
Its primary studied mechanism is mitophagy: the selective removal of damaged or dysfunctional mitochondria by the cell’s recycling system. Rather than boosting mitochondrial activity directly, urolithin A prompts the cell to identify and dispose of worn-out mitochondria, making room for healthier replacements. This quality-control process tends to decline with age. Animal work published in Nature Medicine demonstrated that urolithin A induces mitophagy and extended lifespan in C. elegans, and improved muscle function in rodent models [3].
In humans, a phase I trial found the compound was safe and produced molecular signatures consistent with improved mitochondrial and cellular health, including changes in mitochondrial gene expression [4]. A subsequent randomized trial in middle-aged adults showed improvements in muscle strength, exercise performance, and circulating biomarkers of mitochondrial health compared to placebo [1]. Research has also explored urolithin A’s role in ER-mitochondria communication and calcium handling in neuronal cells under stress conditions [5].
How Nicotinamide Riboside Works: Raising NAD+ Levels
Nicotinamide riboside is a form of vitamin B3 that serves as a precursor to NAD+ (nicotinamide adenine dinucleotide), a coenzyme central to energy metabolism and a substrate for proteins called sirtuins and PARPs that regulate cellular stress responses and DNA repair. NAD+ levels measurably decline with age in human tissues, and the hypothesis behind NR supplementation is that restoring those levels might counteract some downstream effects of that decline.
Early research in mice showed NR enhanced oxidative metabolism and offered protection against high-fat diet-induced obesity [6]. The mechanism involves NR being converted through a biosynthetic pathway into NAD+, which then supports mitochondrial energy production and other cellular functions [7]. However, raising NAD+ levels in blood does not automatically translate into the same increases inside cells or specific tissues, and this distinction matters for interpreting trials.
Human trials have confirmed that NR supplementation reliably raises blood NAD+ metabolite levels. In older adults, NR augmented the skeletal muscle NAD+ metabolome and produced transcriptomic and anti-inflammatory changes [8]. A randomized trial in Parkinson’s disease patients found that NR increased brain NAD+ levels and was well tolerated, though clinical benefit remains under investigation [9].
What Human Trials Have Found on Muscle and Physical Function
Muscle health is a shared area of interest for both compounds, since mitochondrial decline is closely tied to age-related muscle loss (sarcopenia). The available human evidence differs in depth and specificity between the two.
For urolithin A, a randomized controlled trial in middle-aged adults reported statistically significant improvements in muscle strength and endurance exercise performance alongside changes in mitochondrial health biomarkers compared to placebo [1]. This is a relatively direct test of functional outcomes rather than just biomarker changes.
For NR, a 2025 systematic review and meta-analysis of NR and NMN (a related NAD+ precursor) on skeletal muscle mass and function found the overall evidence mixed, with some positive signals on muscle function but heterogeneity across trials limiting firm conclusions [2]. A separate trial found NR supplementation altered body composition and skeletal muscle acetylcarnitine concentrations in healthy obese adults, though without a clear improvement in functional performance [10]. The honest summary is that NR reliably raises NAD+ metabolites; whether that translates into meaningful muscle function improvements in humans is still being worked out.
Mechanisms Side by Side: Cleanup vs. Replenishment
The conceptual difference between the two compounds is worth making explicit. Urolithin A operates primarily through mitophagy—a cellular housekeeping process that removes damaged mitochondria. Think of it as quality control: prompting the cell to clear out dysfunctional components so that healthier mitochondria can replace them [3] [11]. This does not directly add fuel or substrates to mitochondria; it improves the overall quality of the mitochondrial pool.
NR works upstream by providing a building block for NAD+, a molecule that mitochondria and other cellular systems use as a cofactor in hundreds of reactions. This is more of a substrate-replenishment strategy—attempting to restore a resource that declines with age. The two approaches are not mutually exclusive in theory, and some researchers have speculated about potential complementarity, though combined human trials are not yet available in the published evidence provided here.
Neither mechanism is inherently superior. The relevance of each depends on what is actually limiting function in a given tissue or individual, something that cannot be determined by supplementation alone.
Safety and Tolerability: What Trials Report
Both compounds have been evaluated for safety in human trials and appear generally well tolerated at studied doses. For urolithin A, a phase I trial in healthy adults found no safety concerns and identified molecular signals of improved cellular health [4]. For NR, trials including those in older adults and people with Parkinson’s disease have reported acceptable tolerability profiles [8] [9].
That said, the longest human trials for both compounds are measured in weeks to a few months, not years. Long-term safety data are limited for both. Neither compound has been evaluated in all population groups, including people with serious chronic illnesses, those on multiple medications, or pregnant and breastfeeding individuals. Dose-response relationships are not fully characterized for either compound in humans.
Gaps, Limitations, and What We Don't Know
It is important to read the evidence for both compounds with appropriate skepticism about what has not yet been shown. Animal results—even compelling ones—do not always translate to humans. Biomarker changes in blood do not always reflect what is happening inside tissues. And short trials measuring surrogate endpoints cannot tell us whether either compound reduces meaningful long-term outcomes like disease incidence or mortality.
For urolithin A, one significant open question is bioavailability variation: because gut bacteria drive natural production, individuals without the relevant microbial populations may absorb or respond to supplemental forms differently. Research into gut microbiome interactions and optimal dosing continues. Additionally, most human trials have focused on muscle and mitochondrial biomarkers; evidence in other organ systems, including the brain and cardiovascular system, is largely preclinical at this stage [11].
For NR, a persistent question is whether blood NAD+ increases translate into functional NAD+ increases inside target tissues. Research suggests that NAD+ synthesis and breakdown fluxes are tightly regulated in cells [7], which may limit how much supplementation actually shifts intracellular levels. The 2025 meta-analysis on muscle outcomes reflects this uncertainty in a practical context [2].
🛒 Where to Buy Urolithin A
- Timeline Mitopure SoftgelsClinically studied
softgels, 500 mg/day — The clinically studied form (Amazentis); used in the human trials. - Pure Encapsulations Renual
caplique capsules, 250 mg Mitopure Urolithin A/serving (with resveratrol + CoQ10) — established clinical-supplement brand, third-party tested. - ProHealth Longevity Urolithin A
capsules, 500 mg — Longevity-focused brand, often higher dose. - Double Wood Urolithin A
capsules, 250-500 mg — Budget-friendly, widely available, COA on request.
As an Amazon Associate we earn from qualifying purchases. Prices and availability vary; verify dose and third-party testing before buying.
A Note on the Evidence
The evidence for both urolithin A and nicotinamide riboside is promising but mostly based on short-term trials with biomarker and performance endpoints—neither compound has been shown to prevent or treat any disease in humans. If you have a chronic health condition, take medications, or are pregnant or breastfeeding, speak with your doctor before adding either supplement to your routine.
Frequently Asked Questions
What is the main difference between urolithin A and nicotinamide riboside?
Urolithin A primarily works by activating mitophagy—the cell’s process for removing and recycling damaged mitochondria—while NR works by raising levels of NAD+, a coenzyme that mitochondria and many other cellular processes depend on [3] [6]. One is a quality-control mechanism; the other is a substrate-replenishment strategy.
Does urolithin A actually improve muscle function in humans?
A randomized controlled trial in middle-aged adults found that urolithin A supplementation improved muscle strength, endurance exercise performance, and biomarkers of mitochondrial health compared to placebo [1]. This is promising, though the trial was relatively short-term and further research is ongoing.
Does nicotinamide riboside improve muscle strength?
NR consistently raises NAD+ metabolite levels in skeletal muscle and blood in human studies [8], but a 2025 systematic review and meta-analysis found mixed evidence on whether this translates into meaningful improvements in muscle mass or function [2]. The functional evidence is less consistent than the biomarker evidence.
Can urolithin A and NR be taken together?
No human trials in the available evidence have specifically tested the combination, so there is no published data on whether combining them offers additive or synergistic benefit. Because they work through different mechanisms, the combination is biologically plausible to explore, but this would need proper clinical evaluation before any claim about combined benefit could be made.
Is urolithin A safe?
A phase I trial in healthy adults found urolithin A to be safe and well tolerated at studied doses, with molecular signatures suggesting improved mitochondrial and cellular health rather than harm [4]. As with NR, long-term safety data beyond several months are not yet available, and individuals with health conditions should consult a physician before supplementing.
Who produces urolithin A naturally from food?
Urolithin A is produced in the gut from ellagitannins found in pomegranates, walnuts, and certain berries, but only by individuals with the right gut bacteria. Research on urolithin A as reviewed in Trends in Molecular Medicine notes that significant variation exists in who produces it naturally, which is part of the rationale for developing supplemental forms [11].
References
- Singh A et al. Urolithin A improves muscle strength, exercise performance, and biomarkers of mitochondrial health in a randomized trial in middle-aged adults. Cell reports. Medicine (2022). PMID 35584623
- Prokopidis K et al. The Effect of Nicotinamide Mononucleotide and Riboside on Skeletal Muscle Mass and Function: A Systematic Review and Meta-Analysis. Journal of cachexia, sarcopenia and muscle (2025). PMID 40275690
- Ryu D et al. Urolithin A induces mitophagy and prolongs lifespan in C. elegans and increases muscle function in rodents. Nature medicine (2016). PMID 27400265
- Andreux PA et al. The mitophagy activator urolithin A is safe and induces a molecular signature of improved mitochondrial and cellular health in humans. Nature metabolism (2019). PMID 32694802
- Lee HJ et al. Urolithin A suppresses high glucose-induced neuronal amyloidogenesis by modulating TGM2-dependent ER-mitochondria contacts and calcium homeostasis. Cell death and differentiation (2021). PMID 32704090
- Cantó C et al. The NAD(+) precursor nicotinamide riboside enhances oxidative metabolism and protects against high-fat diet-induced obesity. Cell metabolism (2012). PMID 22682224
- Liu L et al. Quantitative Analysis of NAD Synthesis-Breakdown Fluxes. Cell metabolism (2018). PMID 29685734
- Elhassan YS et al. Nicotinamide Riboside Augments the Aged Human Skeletal Muscle NAD(+) Metabolome and Induces Transcriptomic and Anti-inflammatory Signatures. Cell reports (2019). PMID 31412242
- Brakedal B et al. The NADPARK study: A randomized phase I trial of nicotinamide riboside supplementation in Parkinson's disease. Cell metabolism (2022). PMID 35235774
- Remie CME et al. Nicotinamide riboside supplementation alters body composition and skeletal muscle acetylcarnitine concentrations in healthy obese humans. The American journal of clinical nutrition (2020). PMID 32320006
- D'Amico D et al. Impact of the Natural Compound Urolithin A on Health, Disease, and Aging. Trends in molecular medicine (2021). PMID 34030963
These statements have not been evaluated by the Food and Drug Administration. This information is not intended to diagnose, treat, cure, or prevent any disease. Content is for informational purposes only and is not medical advice; consult a qualified healthcare provider before starting any supplement. As an Amazon Associate we earn from qualifying purchases.