what-is-urolithin-b

Cellular Longevity Series · Vitality Supplements

What is Urolithin B?

Urolithin B (CAS 1139-83-9) is a naturally occurring postbiotic compound produced when gut bacteria metabolise ellagitannins from pomegranate and other plants. Not everyone produces it efficiently from food — direct supplementation bypasses that variability.

CAS1139-83-9
C13H8O3Molecular formula
🌿Postbiotic
300mgPer serving

Quick Answer

Urolithin B (CAS 1139-83-9) is a postbiotic benzocoumarin produced by gut bacteria from ellagitannins in pomegranate, walnuts, and other plants. It has a hydroxyl group at position 3 only. Not everyone converts dietary ellagitannins into urolithins — estimated 30–40% of people are non-producers. It is a food supplement, not a medicine.

The basics

What is Urolithin B?

Urolithin B is a naturally occurring compound with the CAS number 1139-83-9 and molecular formula C13H8O3. It belongs to a class of compounds called urolithins — polyphenolic benzocoumarins produced by gut microbiota from ellagitannins found in pomegranate, walnuts, raspberries, and certain other plants.

Urolithins are not found directly in foods. They are metabolic end-products produced when specific gut bacteria break down ellagitannins and ellagic acid. The urolithin produced depends on the individual's gut microbiome composition — and crucially, not everyone produces urolithins efficiently. Estimated 30–40% of people lack the gut bacteria needed to convert dietary ellagitannins into urolithins at meaningful levels. Direct supplementation with Urolithin B bypasses this conversion step entirely.

Urolithin B is classified as a postbiotic — a stable, biologically active metabolite produced by gut microbiota from plant polyphenols. Unlike probiotics (live bacteria) or prebiotics (dietary fibre), postbiotics require no refrigeration and have no viability concerns.

Key distinction: Urolithin B (position 3 hydroxyl only) differs structurally from Urolithin A (positions 3 and 8). This is not a superior or inferior distinction — they are different compounds with different research profiles. Urolithin A has a substantially larger published human research base. See our Urolithin A vs Urolithin B comparison for the full breakdown.

  • CAS number: 1139-83-9
  • Molecular formula: C13H8O3
  • Chemical class: Urolithin, benzocoumarin
  • Hydroxylation: Position 3 only
  • Source: Gut bacteria metabolism of ellagitannins from pomegranate, walnuts, raspberries
  • Classification: Postbiotic
  • Gut production variability: ~30–40% of people are non-producers
  • Regulatory status: Food supplement (UK)

Compound class

What are urolithins?

Urolithins are a class of polyphenolic compounds — specifically benzocoumarins — produced exclusively by gut microbiota from ellagitannins and ellagic acid. They are not present in foods themselves. They are metabolic products that only exist after gut bacteria have broken down dietary precursors.

Four main urolithins have been identified: Urolithin A, Urolithin B, Urolithin C, and Urolithin D. Urolithins A and B are the most studied. The urolithins produced by an individual depend entirely on their gut microbiome composition — which varies significantly between people and can change over time.

Urolithin A · CAS 1143-70-0
Hydroxyl at positions 3 & 8
The most studied urolithin. Has a substantially larger published human research base than Urolithin B. Both hydroxyl positions present.
Urolithin B · CAS 1139-83-9
Hydroxyl at position 3 only
Structurally distinct from Urolithin A. Research is at an earlier stage with most published work preclinical. This is the compound in Vitality Supplements.
Urolithin C & D
Less studied compounds
Urolithins C and D have additional hydroxyl groups. They are produced in smaller quantities and have a much more limited research base.

Compound category

What is a postbiotic?

A postbiotic is a biologically active compound produced by gut microbiota from dietary substrates. The term was formally defined by the International Scientific Association for Probiotics and Prebiotics (ISAPP) in 2021 as "a preparation of inanimate microorganisms and/or their components that confers a health benefit on the host."

Urolithin B is classified as a postbiotic because it is a defined metabolite produced by gut bacteria from plant polyphenols (ellagitannins). It differs from probiotics and prebiotics in several important ways.

Probiotics
Live bacteria
Live microorganisms that must remain viable to be effective. Require refrigeration. Viability can degrade over time and through the digestive process.
Prebiotics
Dietary fibre
Non-digestible fibres that feed gut bacteria. Found in oats, garlic, onions, and other plant foods. Support the conditions for bacterial activity.
Postbiotics
Stable metabolites
Defined compounds produced by gut bacteria from dietary substrates. Stable at room temperature. No viability concerns. Urolithin B is a postbiotic.

Why supplement directly

The gut conversion problem

Urolithin B cannot be obtained directly from food. It is only produced when specific gut bacteria metabolise ellagitannins from pomegranate, walnuts, and other plants. The efficiency of this conversion varies dramatically between individuals — and a significant proportion of people cannot produce meaningful quantities of urolithins at all.

Research suggests that approximately 30–40% of people lack the specific gut bacteria (including strains of Gordonibacter, Ellagibacter, and related species) needed to convert ellagitannins into urolithins. Even among those who do produce urolithins, the quantities produced from dietary sources alone are typically modest and variable.

Direct supplementation with Urolithin B bypasses gut conversion entirely — delivering a defined, consistent dose regardless of individual microbiome composition.

Dietary sources of ellagitannins: Pomegranate (Punica Granatum) is the richest known source. Other sources include walnuts, raspberries, strawberries, blackberries, and oak-aged wines. However, the ellagitannin content varies considerably between sources, and conversion to urolithins depends entirely on gut microbiome composition.

People also ask

Common questions about Urolithin B

What does Urolithin B do?

Urolithin B is a food supplement that contributes to digestive wellness and supports normal cellular function. It is not a medicine and does not treat any disease. As a postbiotic derived from pomegranate ellagitannins, it is produced by gut bacteria — or supplied directly through supplementation for those who cannot produce it efficiently.

Is Urolithin B better than Urolithin A?

This is not a better/worse distinction — they are structurally different compounds with different research profiles. Urolithin A has a substantially larger published human research base. Urolithin B research is at an earlier stage. See our full comparison for a detailed breakdown.

Can you get Urolithin B from pomegranate juice?

Not directly. Urolithin B is produced by gut bacteria from ellagitannins in pomegranate — it is not present in the fruit or juice itself. Whether you produce urolithins from pomegranate depends on your gut microbiome. Estimated 30–40% of people cannot produce meaningful quantities from dietary sources.

How long does Urolithin B take to work?

Urolithin B acts at a cellular level and is not a stimulant. Most customers report no immediate noticeable change. The compound is best assessed over months of consistent daily use, not days. Cellular support supplements are long-term additions to a health routine.

Usage

How to take Urolithin B

Vitality Supplements Urolithin B provides 300mg per serving across 2 vegan HPMC capsules. Each pouch contains 60 capsules providing 30 servings.

  • Take 2 capsules daily with water, preferably with food
  • Consistent daily use recommended
  • Do not exceed the stated recommended daily dose
  • Consult your GP before use if pregnant, breastfeeding, on medication, or have a health condition
🔬3rd Party TestedEvery batch
🇬🇧UK ManufacturedPremium quality
🌱100% VeganHPMC capsules
↩60-Day GuaranteeNo questions asked

Full FAQ

Frequently asked questions

What is Urolithin B?

Urolithin B (CAS 1139-83-9) is a naturally occurring postbiotic compound produced when gut bacteria metabolise ellagitannins from pomegranate, walnuts, and other plants. It is a urolithin — a class of benzocoumarins. Not everyone converts dietary ellagitannins efficiently, so direct supplementation bypasses this variability. It is a food supplement, not a medicine.

What is the difference between Urolithin A and Urolithin B?

Urolithin A (CAS 1143-70-0) has hydroxyl groups at positions 3 and 8. Urolithin B (CAS 1139-83-9) has a hydroxyl group at position 3 only. Urolithin A has a substantially larger published human research base. Urolithin B research is at an earlier stage. See our Urolithin A vs Urolithin B comparison guide for more.

What foods contain Urolithin B?

No foods contain Urolithin B directly. It is produced by gut bacteria from ellagitannins in pomegranate, walnuts, raspberries, and other plants. Whether you produce it depends on your gut microbiome — an estimated 30–40% of people cannot produce meaningful quantities from dietary sources.

What is the CAS number for Urolithin B?

The CAS number for Urolithin B is 1139-83-9. The molecular formula is C13H8O3.

Is Urolithin B a postbiotic?

Yes. Urolithin B is classified as a postbiotic — a biologically active metabolite produced by gut microbiota from plant polyphenols. Unlike probiotics (live bacteria) or prebiotics (fibre), postbiotics are stable, well-defined compounds requiring no refrigeration.

Is Urolithin B vegan?

Vitality Supplements Urolithin B is encapsulated in HPMC vegan capsules and is free from gluten, GMOs, dairy, soy, artificial colours and preservatives. It is suitable for vegans.

Is Urolithin B third-party tested?

Yes. Every batch of Vitality Supplements Urolithin B is tested at an ISO-accredited independent laboratory. A Certificate of Analysis is available on request.

Is Urolithin B a medicine?

No. Urolithin B is a food supplement. It does not treat, cure, or prevent any disease or medical condition. If you have a health concern, consult your GP.

Can I take Urolithin B with NMN?

Many customers combine Urolithin B with NMN and other Vitality Supplements products. Consult a healthcare professional if you are on medication or have a health condition.

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Related guides

Cellular Longevity · Comparison Urolithin A vs Urolithin B A detailed comparison — structural differences, hydroxylation patterns, research profiles, and which makes sense for direct supplementation. Cellular Longevity Series · Vitality Supplements Shop Urolithin B 300mg per serving. 60 vegan capsules. Third-party tested. UK manufactured. 60-day guarantee.

Cellular Longevity Series · Vitality Supplements

Urolithin B 300mg

300mg per serving · 60 vegan capsules · 30 servings · Third-party tested · UK manufactured · 60-day guarantee

Shop Urolithin B

This page is for informational purposes only. Urolithin B is a food supplement. Food supplements should not be used as a substitute for a varied diet and healthy lifestyle. Urolithin B is not a medicine and does not treat, cure, or prevent any disease. If you are pregnant, breastfeeding, taking medication, or have a medical condition, consult your GP before use. Store out of reach of children.