The immune system does not age gracefully. From the sixth decade of life onward, most people experience a gradual decline in immune competence—a process researchers call immunosenescence—that leaves the body less able to respond to infections, less responsive to vaccines, and more prone to chronic low-grade inflammation. Finding ways to slow or partially reverse this decline is one of the more active areas of aging research.
Urolithin A, a compound produced in the gut when certain polyphenol-rich foods are consumed, has attracted scientific interest largely because of its ability to induce mitophagy—the cellular process by which damaged mitochondria are identified and cleared. Mitochondrial dysfunction is increasingly understood as a driver of immune aging, and a small but growing body of research is now examining whether urolithin A can translate its cellular effects into measurable improvements in immune function. This article summarizes what that research currently shows, and where important questions remain.
Key Takeaways
- Urolithin A induces mitophagy—the cellular clearance of damaged mitochondria—which is one proposed mechanism by which it may support immune cell function with age.
- A 2025 randomized, placebo-controlled trial in Nature Aging examined urolithin A’s effect on age-related immune decline, representing the first significant human clinical evidence in this area [8].
- Multiple preclinical studies show that urolithin A improves CD8+ T cell fitness and longevity through distinct molecular pathways including ERK1/2-ULK1 and FOXO1 signaling [PMID 38447147, PMID 38626334, PMID 36351375].
- Not everyone can convert polyphenol-rich foods into urolithin A efficiently; gut microbiome composition, which changes with age, is the determining factor [7].
- The evidence is promising but still early: most mechanistic research has been conducted in preclinical models or cancer-focused settings, and larger, longer human trials are needed to confirm effects on everyday immune aging.
Immunosenescence and the Mitochondrial Connection
Immune cells are unusually dependent on mitochondria. T cells, which coordinate adaptive immune responses, must rapidly shift between resting and activated states—a metabolic demand that requires healthy, functional mitochondria. Natural killer cells, macrophages, and neutrophils similarly rely on mitochondrial energy production to carry out their roles. When mitochondria accumulate damage over decades of use, immune cell function suffers alongside them.
Research published in Nature Aging found that inducing mitochondrial recycling—essentially prompting cells to discard dysfunctional mitochondria and build fresh ones—was associated with reversing age-associated decline in both the hematopoietic system and broader immune function in preclinical models [2]. The hematopoietic system is the bone-marrow-based factory that produces all blood and immune cells, so impairment there has downstream consequences across the entire immune architecture. This work helped frame mitophagy induction as a plausible target for immune rejuvenation strategies.
How Urolithin A Triggers Mitophagy
Mitophagy is the selective form of autophagy—cellular self-cleaning—directed specifically at mitochondria. When a mitochondrion loses its membrane potential or accumulates excessive damage, it is tagged for degradation and engulfed by a structure called an autophagosome, which fuses with a lysosome to break down and recycle the components. In aging cells, this clearance process becomes sluggish, allowing damaged mitochondria to accumulate and release inflammatory signals.
Urolithin A appears to stimulate mitophagy through several molecular pathways. One study identified an ERK1/2-ULK1 signaling cascade as a key route by which urolithin A enhances the fitness of CD8+ T cells, a critical class of cytotoxic immune cells [3]. Another line of work has linked urolithin A’s mitophagy effects to activation of TFEB, a transcription factor that regulates lysosomal function—the downstream machinery that actually degrades cleared mitochondria [4]. Understanding these mechanisms matters because it provides a plausible biological rationale for why urolithin A might affect immune cell performance, rather than leaving the observed effects unexplained.
It is worth noting that urolithin A is not found ready-made in food. It is produced from ellagitannins and ellagic acid—found in pomegranates, walnuts, and certain berries—by specific gut bacteria. Not everyone harbors the bacterial populations needed for this conversion, and production efficiency varies widely between individuals [7]. This is part of the reason researchers have moved toward studying urolithin A as a direct supplement rather than relying on dietary intake.
Clinical Evidence: A Randomized Controlled Trial
The most direct human evidence on urolithin A and immune aging comes from a randomized, placebo-controlled trial published in Nature Aging in 2025, which examined whether urolithin A supplementation could reduce age-related immune decline [8]. A subsequent author correction was published in 2026 [9], which is a normal part of the scientific publication process and does not indicate retraction.
Randomized controlled trials occupy the highest tier of clinical evidence, so this study marks a meaningful step beyond the preclinical and observational work that had preceded it. The trial’s focus on age-related immune decline rather than a specific disease makes the findings more directly relevant to the general question of whether urolithin A can support immune health in aging adults. That said, a single trial—however well-designed—is the beginning of an evidence base, not the end of it. Replication and longer-term follow-up will be needed before firm conclusions can be drawn about the size and durability of any effects.
CD8+ T Cells: The Immune Subset Most Studied
Several research groups have focused specifically on CD8+ T cells—also called cytotoxic T lymphocytes—as the immune population most affected by urolithin A. These cells are responsible for identifying and destroying infected or malignant cells, and their functional decline with age is a well-documented feature of immunosenescence.
A study in Immunity found that urolithin A-induced mitophagy promoted the expansion of T memory stem cells, a long-lived T cell subset, and that these cells showed superior functional capacity in preclinical models [1]. A separate study found that urolithin A promoted CD8+ T cell-mediated cancer immunosurveillance through activation of FOXO1, a transcription factor involved in T cell longevity and self-renewal [5]. A third group demonstrated that urolithin A improved CD8+ T cell fitness via the ERK1/2-ULK1 signaling cascade [3]. Taken together, these findings suggest a consistent pattern: urolithin A appears to support a cell type that tends to become exhausted and dysfunctional with normal aging.
It is important to be precise about what these studies do and do not show. Much of this CD8+ T cell work was conducted in the context of cancer immunology, using models designed to study antitumor immunity rather than everyday immune aging. Whether the improvements in T cell fitness observed in those settings translate directly to better responses to respiratory infections or vaccines in older adults remains to be established in dedicated clinical trials.
Innate Immunity: Macrophages and Microglial Cells
The adaptive immune system—where T cells operate—is not the only branch affected by aging. The innate immune system, which provides faster, less specific defenses, also declines with age. Macrophages, which are innate immune cells found in tissues throughout the body, become less effective at clearing pathogens and debris while simultaneously becoming more prone to chronic inflammatory signaling.
One study found that urolithin A inhibited breast cancer progression by activating TFEB-mediated mitophagy specifically within tumor-associated macrophages, shifting their functional state [4]. While this was studied in a cancer context, it illustrates that urolithin A can influence macrophage biology through mitophagy pathways. In the brain, a specialized form of macrophage called microglia manages local immune surveillance. Research comparing urolithin A and nicotinamide riboside found that the two compounds differentially regulated innate immune defenses and metabolism in human microglial cells, with urolithin A producing distinct effects on this cell type [6]. This line of research is early-stage but points toward urolithin A having immune-relevant effects beyond the adaptive T cell compartment.
Gut Microbiota, Dietary Sources, and Supplementation
Because urolithin A is a microbiome-derived metabolite, its availability in the body is tied to gut bacterial composition. Research on the relationship between gut microbiota and aging highlights that the gut microbiome changes substantially with age, and that these changes affect the production of bioactive metabolites from dietary polyphenols [7]. Older adults may produce less urolithin A from food sources even when eating diets rich in pomegranate or walnuts, precisely because of age-related shifts in microbiome composition.
This has driven interest in bypassing gut conversion entirely by supplementing with urolithin A directly. Standardized urolithin A supplements are commercially available and have been used in the clinical trials described here. If you are considering supplementation, the relevant questions—appropriate dose, duration, and suitability for your individual health circumstances—are best discussed with a healthcare provider, as the clinical evidence base is still developing.
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- Timeline Mitopure SoftgelsClinically studied
softgels, 500 mg/day — The clinically studied form (Amazentis); used in the human trials. - DoNotAge Pure Urolithin A
capsules, 250-500 mg — Popular longevity-brand generic, third-party tested. - ProHealth Longevity Urolithin A
capsules, 500 mg — Longevity-focused brand, often higher dose. - Double Wood Urolithin A
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A Note on the Evidence
The clinical evidence for urolithin A and immune aging remains limited in scale and follow-up duration; most mechanistic findings come from preclinical or cancer-focused studies that may not fully translate to everyday immune health in older adults. People with immune conditions, those taking immunosuppressant medications, or anyone with serious illness should consult a qualified healthcare provider before beginning any new supplement.
Frequently Asked Questions
What is urolithin A and where does it come from?
Urolithin A is a compound produced in the human gut when bacteria metabolize ellagitannins and ellagic acid found in foods like pomegranates, walnuts, and certain berries. Because it depends on specific gut bacteria for its production, not everyone converts these foods into urolithin A efficiently, and output declines with age-related microbiome changes [7].
How might urolithin A support immune function?
The primary proposed mechanism is mitophagy—the selective removal of damaged mitochondria from cells. Immune cells depend heavily on healthy mitochondria to function, and research suggests that inducing mitochondrial recycling can reverse some age-associated immune decline [2]. Urolithin A appears to stimulate this process through pathways including ERK1/2-ULK1 signaling and TFEB activation [PMID 38447147, PMID 38615740].
Has urolithin A been tested in humans for immune aging?
Yes. A randomized, placebo-controlled trial published in Nature Aging in 2025 directly examined whether urolithin A could reduce age-related immune decline [8]. A subsequent author correction was issued in 2026 [9], which is a routine scientific process. Human evidence is still limited in scope and duration, and this area of research is actively developing.
Which immune cells has urolithin A been most studied in?
CD8+ T cells—cytotoxic immune cells that destroy infected or cancerous cells—have received the most research attention. Studies have found that urolithin A-induced mitophagy expands T memory stem cells [1], promotes CD8+ T cell-mediated surveillance via FOXO1 [5], and improves T cell fitness via ERK1/2-ULK1 signaling [3]. Macrophages and microglial cells have also been studied [PMID 38615740, PMID 39665042].
Is there a difference between getting urolithin A from food versus a supplement?
Functionally, the molecule is the same, but the amount produced from food varies significantly based on individual gut microbiome composition. Some people convert pomegranate ellagitannins efficiently; others produce very little urolithin A regardless of diet. Supplements deliver urolithin A directly, bypassing this conversion step, and were the form used in the clinical trials cited here.
Can urolithin A prevent or treat immune-related diseases?
No such claims are supported by current evidence. The research describes cellular mechanisms and early clinical signals, not proven disease prevention or treatment. Much of the T cell research has been conducted in cancer immunology models, and it is not established whether those findings translate to outcomes like vaccine response or infection resistance in aging adults. This content is informational and not a substitute for medical advice.
References
- Denk D et al. Expansion of T memory stem cells with superior anti-tumor immunity by Urolithin A-induced mitophagy. Immunity (2022). PMID 36351375
- Girotra M et al. Induction of mitochondrial recycling reverts age-associated decline of the hematopoietic and immune systems. Nature aging (2023). PMID 37653255
- Ma S et al. Urolithin A Hijacks ERK1/2-ULK1 Cascade to Improve CD8(+) T Cell Fitness for Antitumor Immunity. Advanced science (Weinheim, Baden-Wurttemberg, Germany) (2024). PMID 38447147
- Zheng B et al. Urolithin A inhibits breast cancer progression via activating TFEB-mediated mitophagy in tumor macrophages. Journal of advanced research (2025). PMID 38615740
- Ginefra P et al. Urolithin-A Promotes CD8+ T Cell-mediated Cancer Immunosurveillance via FOXO1 Activation. Cancer research communications (2024). PMID 38626334
- Madsen HB et al. Urolithin A and nicotinamide riboside differentially regulate innate immune defenses and metabolism in human microglial cells. Frontiers in aging neuroscience (2024). PMID 39665042
- Beaver LM et al. Promotion of Healthy Aging Through the Nexus of Gut Microbiota and Dietary Phytochemicals. Advances in nutrition (Bethesda, Md.) (2025). PMID 39832641
- Denk D et al. Effect of the mitophagy inducer urolithin A on age-related immune decline: a randomized, placebo-controlled trial. Nature aging (2025). PMID 41174221
- Denk D et al. Author Correction: Effect of the mitophagy inducer urolithin A on age-related immune decline: a randomized, placebo-controlled trial. Nature aging (2026). PMID 41491872
