Your cells run on mitochondrial energy all day. When those tiny engines wear down with age or stress, performance dips and recovery slows. That is why interest in urolithins has grown. These gut-derived metabolites of ellagitannins appear to support cellular maintenance and muscle function from the inside out. Two forms matter most in supplements and in the scientific literature, Urolithin A and Urolithin B. If you are comparing Urolithin A vs Urolithin B, the real difference is that Urolithin A mainly supports mitochondrial quality control through mitophagy, while Urolithin B more directly influences muscle protein balance and resilience. Understanding how they diverge helps you decide whether to use one or both.

What Urolithins are and where they come from

Ellagitannins from pomegranate, walnuts, and certain berries are transformed by specific gut microbes into urolithins. Not everyone produces them equally, which is one reason standardized supplementation has become popular. BioLight sources its urolithins from pomegranate peel, the richest portion of the plant in ellagitannin precursors, to deliver consistent exposure regardless of your microbiome.

How Urolithin A works inside cells

Urolithin A’s signature is mitophagy, the cellular housekeeping program that tags and recycles worn mitochondria so a cleaner, more efficient pool can take their place. Early human evidence showed this signal appears quickly. In a first-in-human study reported in Nature Metabolism in 2019, four weeks of daily Urolithin A in older adults activated mitochondrial gene networks in skeletal muscle and shifted plasma acylcarnitines, a pattern consistent with improved mitochondrial quality control. Longer randomized trials connected those molecular changes to function. In JAMA Network Open in 2022, adults aged 65 to 90 improved muscle endurance after four months and showed lower C-reactive protein, a marker of systemic inflammation. In Cell Reports Medicine in 2022, sedentary middle-aged adults improved muscle strength and exercise performance over four months, with proteomic evidence that mitochondrial pathways were upregulated. This arc is consistent across publications, cellular signatures in weeks, practical stamina and recovery gains in months, and a neutral to favorable safety profile.

How Urolithin B works and why it is different

Urolithin B shows a complementary profile that is more muscle-centric. In preclinical studies, Urolithin B has promoted muscle protein synthesis, reduced protein breakdown, and helped preserve lean mass during catabolic stress. A widely cited paper in Scientific Reports in 2017 reported that Urolithin B increased muscle growth and inhibited atrophy pathways in cell and animal models, with signals pointing toward mTOR and reduced ubiquitin-proteasome activity. Follow-up work in pharmacology journals has described anti-inflammatory and antioxidant effects in muscle and neural tissue. Human trials with Urolithin B alone are still limited, so its evidence base is earlier than Urolithin A’s, yet the mechanistic direction is consistent. Think of Urolithin B as support for muscle protein balance and cellular resilience that pairs naturally with Urolithin A’s mitochondrial maintenance.

Urolithin A vs Urolithin B, which is better

Neither is universally better. They pull on different levers that matter for performance and healthy aging.

• Choose Urolithin A if your priority is mitochondrial quality control, endurance capacity, recovery, and systemic inflammatory tone. The human trials that measured those outcomes used Urolithin A.
• Choose Urolithin B if your interest leans toward muscle protein preservation, anti-catabolic support, and complementary cellular resilience, noting that most evidence is preclinical.
• Choose a combination if you want the maintenance plus capacity model, clearing inefficient mitochondria while supporting an anabolic environment inside muscle.

Why stacking both often makes sense

Mitochondria remodel through two linked phases, cleanup and rebuild. Urolithin A supports cleanup through mitophagy, which lowers the oxidative cost of producing ATP. Urolithin B supports the rebuild side by nudging muscle protein turnover toward synthesis and by calming inflammatory signals that slow repair. Training amplifies both, since exercise naturally stimulates mitochondrial biogenesis and muscle remodeling. When these inputs are aligned, the average quality of the mitochondrial network rises and muscle tissue has an easier time keeping up with daily demands.

What you might feel and when

Expect a slow, steady ramp rather than a surge.

• Weeks 1 to 4: most changes are inside cells. People often report slightly smoother easy efforts, less leg heaviness on stairs, and a touch faster bounce-back after routine activity. This matches the early mitochondrial signatures seen with Urolithin A in Nature Metabolism.
• Weeks 8 to 12: stamina and repeatability become easier to notice. Holding zone-2 cardio at the same heart rate, adding a small set to resistance work without next-day drag, and shorter soreness windows are common reports.
• Months 3 to 4: functional gains are clearer. The four-month trials that improved endurance and strength align with real-world experiences of more consistent training weeks and fewer off days.

Safety snapshots and realistic limits

Published human studies of Urolithin A in older and middle-aged adults report good tolerability from 250 to 1,000 milligrams daily over four to sixteen weeks, stable safety labs, and neutral to favorable patterns in lipids and inflammation. Human evidence for Urolithin B alone is still early. Neither ingredient replaces medical care for cardiometabolic disease, and neither should be expected to produce stimulant-like effects, rapid weight loss, or drug-level changes in glucose or blood pressure.

How BioLithin uses both for a broader effect

BioLithin was formulated to bring the two levers together. It pairs Urolithin A for mitophagy and mitochondrial quality with Urolithin B for muscle metabolism and anti-catabolic support, then adds taurine, an amino acid studied for mitochondrial membrane stability and stress tolerance in muscle and heart. The urolithins are derived from pomegranate peel to maximize ellagitannin density, and the formula is housed in Miron violet glass to help preserve potency. The goal is simple, reinforce cellular cleanup, support muscle repair, and translate those upstream benefits into steadier day-to-day energy, better training repeatability, and healthier aging.

Practical ways to get the most from either form

• Train with intention. Two to four resistance sessions per week with progressive overload plus frequent low to moderate aerobic work provide the stimulus that converts cellular maintenance into performance.
• Distribute protein across meals. Muscle is the largest glucose sink and the tissue where many urolithin benefits are realized. Adequate protein supports the remodeling that reveals those gains.
• Eat a Mediterranean-style pattern. Polyphenols and fiber support vascular health and the microbiome that naturally makes urolithins from food precursors.
• Protect sleep. Deep sleep is when repair programs consolidate changes in mitochondria and muscle proteins.
• Track a light scorecard. Keep one repeatable benchmark workout and note time to fatigue or total work weekly, plus 24 and 48 hour soreness. Small improvements compound.

Key differences at a glance

• Mechanism: Urolithin A, mitophagy and mitochondrial quality control. Urolithin B, muscle protein balance with anti-catabolic and antioxidant support.
• Evidence: Urolithin A, multiple human trials with functional endpoints. Urolithin B, strong preclinical data, limited human data so far.
• Feel: Urolithin A, steadier stamina and recovery over months. Urolithin B, complementary support for strength preservation and training repeatability.
• Best use: Together for a maintenance plus capacity strategy that fits endurance, strength, and healthy aging goals.

Key takeaway

Urolithin A and Urolithin B are not redundant. Urolithin A focuses on cleaning and renewing the mitochondrial network, while Urolithin B helps muscle hold on to strength by improving protein balance and cellular resilience. If you want comprehensive support for energy, performance, and healthy aging, combining them, as in BioLithin, aligns with how your body actually adapts, gradual cleanup, steady rebuild, then noticeable gains in stamina and recovery over the course of two to four months.

This content is for informational purposes only and is not a substitute for medical advice. Always consult a qualified healthcare professional before starting supplementation, especially if you manage health conditions or take prescription medications.