Framing: What Longevity Supplementation Is and Isn't
Longevity supplementation targets the cellular and molecular mechanisms of ageing — not symptoms, but underlying processes. The goal is to slow the rate of biological ageing, extend healthspan (the years lived in good health), and maintain physiological function as chronological age increases.
This is not anti-ageing marketing. The science of cellular senescence, NAD+ decline, mTOR signalling, and autophagy is legitimate, peer-reviewed, and rapidly maturing. What's contested is the degree to which current supplements modulate these pathways meaningfully in humans — the animal data is frequently stronger than the human data.
This guide covers each compound honestly: what the mechanism is, what the animal evidence shows, what the human evidence shows (where it exists), what dosing protocols are used in research, and what a reasonable person can conclude about whether it's worth taking.
1. NMN (Nicotinamide Mononucleotide) and NAD+ Precursors
The NAD+ Problem
NAD+ (nicotinamide adenine dinucleotide) is a coenzyme found in every cell. It's central to energy metabolism (it's the molecule that picks up electrons in the electron transport chain), DNA repair (sirtuins — the longevity proteins — require NAD+ to function), and hundreds of other cellular processes.
NAD+ levels decline with age — by approximately 50% between young adulthood and age 60. This decline is implicated in reduced mitochondrial function, impaired DNA repair, reduced sirtuin activity, and many of the cellular hallmarks of ageing.
The decline is driven by increased consumption (more DNA damage requires more NAD+ for repair) and decreased production. The goal of NAD+ precursor supplementation is to raise intracellular NAD+ back toward youthful levels.
The Precursors: NMN vs NR vs Nicotinamide
NAD+ cannot be taken directly — it doesn't cross cell membranes. The precursors that enter cells and are converted to NAD+ are:
NR (Nicotinamide Riboside): An NAD+ precursor that enters cells via specific transporters (NRK1/NRK2). Well-studied in humans — multiple trials show NR supplementation raises blood NAD+ levels. Cheaper per dose than NMN. Question: does raised blood NAD+ translate to raised intracellular NAD+ in relevant tissues? Evidence suggests yes, but the magnitude varies.
NMN (Nicotinamide Mononucleotide): One step closer to NAD+ in the biosynthesis pathway than NR. For years, the assumption was NMN needed to be converted to NR to enter cells. A 2020 paper identified a specific NMN transporter (Slc12a8) in mouse intestinal cells, allowing direct cellular uptake. Whether this transporter is equivalently active in human tissues remains under investigation.
Human NMN trials: A 2022 Japanese study showed NMN supplementation (250mg/day for 12 weeks) raised blood NAD+ levels in older adults. A Washington University study showed NMN improved muscle insulin sensitivity and physical function in postmenopausal women.
Nicotinamide (standard niacin/B3): A direct NAD+ precursor, cheap, and effective for raising NAD+ levels. However, at higher doses, nicotinamide inhibits sirtuins — the very longevity proteins that require NAD+. This makes standard nicotinamide a poor choice for longevity purposes specifically, despite its effectiveness for NAD+ elevation.
Dosing
NMN: 250–500mg/day. Some protocols use 1,000mg/day. Morning with food. Limited long-term human safety data at higher doses, though short-term trials up to 12 weeks show no significant adverse effects.
NR: 250–500mg/day. Similar evidence base to NMN. More long-term human data available.
Who to believe on NMN vs NR: David Sinclair (Harvard, author of Lifespan) takes NMN. Andrew Huberman takes NMN. Most researchers are agnostic at this stage — both raise NAD+, the superiority of one over the other for human outcomes hasn't been established. NR is cheaper; NMN may have direct cell uptake advantages.
Evidence Strength: Moderate
Animal evidence: Strong. NMN extends lifespan in mice, improves metabolism, physical function, and multiple age-related outcomes. Human evidence: Emerging. Blood NAD+ rises are confirmed. Functional outcomes in humans are more limited but promising.
Interactions
NMN/NR should not be taken with nicotinamide at high doses (sirtuin inhibition competition). Resveratrol (a sirtuin activator) is frequently taken alongside NMN to maximise sirtuin activity while NAD+ is elevated — see below.
2. Resveratrol
The Mechanism
Resveratrol is a polyphenol found in red wine (very low concentrations) and grape skin. It activates SIRT1 (Sirtuin 1), a deacetylase enzyme that regulates gene expression, DNA repair, metabolism, and inflammation. Sirtuins are sometimes called "longevity genes" — they are among the most studied molecular targets in ageing biology.
SIRT1 activation by resveratrol in the presence of elevated NAD+ (from NMN supplementation) is the basis of the Sinclair lab's popular stacking protocol. The logic: NAD+ provides the substrate for sirtuin activity; resveratrol activates SIRT1 to use that substrate.
Evidence
Animal evidence: Compelling. Resveratrol extends lifespan in yeast, roundworms, flies, and some mouse models. Mimics caloric restriction at the molecular level.
Human evidence: Disappointing by comparison. Multiple human trials have failed to show meaningful longevity or metabolic benefits from resveratrol supplementation. A major Cochrane review found limited evidence of cardiovascular benefit. The bioavailability problem — resveratrol is rapidly metabolised in the gut — may explain the translation failure.
Pterostilbene (a methylated analogue of resveratrol) has higher bioavailability (80%+ vs resveratrol's 20-30%) and may be more effective. Some researchers now prefer pterostilbene as the resveratrol replacement in a longevity stack.
Dosing
Standard: 500–1,000mg resveratrol daily. The Sinclair protocol: 1g NMN + 1g resveratrol + 1g metformin (where available) in the morning.
Fat-soluble: Take resveratrol with a fat-containing meal or with olive oil — this substantially improves absorption. Taken without fat, bioavailability is extremely poor.
Evidence Strength: Animal = Strong / Human = Weak
Honest assessment: The animal evidence is remarkable; the human translation has been underwhelming so far. Bioavailability limitations are likely responsible. Pterostilbene may be a better alternative. Take it if the cost is manageable and you want the molecular target covered — but don't rely on it as a primary longevity intervention.
3. Berberine
The Mechanism
Berberine is an alkaloid from several plants (Berberis vulgaris, goldenseal, others). Its primary mechanism is AMPK activation — AMPK (AMP-activated protein kinase) is the cellular energy sensor that becomes activated during caloric restriction and exercise. AMPK activation has downstream effects including:
- Improved insulin sensitivity and glucose regulation
- Activation of autophagy (cellular recycling)
- Reduced mTOR signalling (mTOR drives cellular growth but is associated with accelerated ageing when chronically elevated)
- Reduced inflammation
Berberine is sometimes called "the poor man's metformin" for its similar mechanisms of action. Metformin is the diabetes drug that has attracted significant longevity interest (the TAME trial — Targeting Aging with Metformin — is an ongoing large human study). Berberine activates some of the same pathways.
Evidence
Metabolic: Very strong. Multiple human RCTs show berberine reduces fasting blood glucose, HbA1c, and triglycerides comparably to metformin in type 2 diabetes. Studies show LDL cholesterol reduction of 15–25%.
Longevity pathways: Strong mechanistic evidence in cell and animal studies. Human longevity data doesn't exist yet — it's too early.
Gut microbiome: Berberine significantly modulates the gut microbiome, increasing beneficial bacteria. This is likely part of its metabolic mechanism but adds a gut health dimension.
Dosing
500mg, 2–3× daily with meals. The dosing is critical — berberine has a short half-life and benefits are attenuated by a single large dose. Three smaller doses throughout the day maintain more consistent AMPK activation.
Cycle: Some practitioners recommend cycling berberine (3 months on, 1 month off) due to gut microbiome effects and potential reduction in intestinal enzyme expression with chronic use. Others use it continuously. No definitive answer on this.
Interactions
Berberine inhibits several CYP enzymes (including CYP3A4 and CYP2D6) that metabolise many drugs. If you are on any prescription medication, particularly statins, anticoagulants, or immunosuppressants, check for interactions before using berberine.
Berberine + metformin: combined use amplifies both effects and increases hypoglycaemia risk. Don't combine without medical oversight.
Evidence Strength: Strong for Metabolic Health
One of the most evidence-backed compounds in this stack for human outcomes — not speculative like some longevity supplements. The metabolic benefits are well-documented. The longevity pathway activation is mechanistically solid but not yet proven in human lifespan studies.
4. Spermidine
The Mechanism
Spermidine is a polyamine — a naturally occurring compound found in wheat germ, aged cheese, soy, mushrooms, and other foods. Its primary longevity mechanism is autophagy induction.
Autophagy is the cellular "self-eating" process — cells break down damaged components, recycle them, and maintain quality control. Autophagy declines with age, leading to accumulation of damaged proteins and organelles. Caloric restriction and fasting are the most powerful known activators of autophagy. Spermidine appears to activate autophagy via a similar (though not identical) pathway.
Evidence
Animal evidence: Strong. Spermidine supplementation extends lifespan in yeast, nematodes, flies, and mice. The effect is abolished when autophagy pathways are blocked, confirming the mechanism.
Human evidence: Limited but encouraging. An Austrian observational study found higher dietary spermidine intake associated with lower all-cause mortality. A small human trial showed cognitive improvement in older adults with subjective cognitive decline. Cardiovascular studies are in early stages.
Dosing
Dietary spermidine is found in: wheat germ (highest), soy, peas, corn, mushrooms, aged cheese. Supplemental spermidine from wheat germ extract: 1–2mg/day (the amount reflecting higher dietary intake populations).
Note: supplemental spermidine doses used in many human-health applications are modest — far below doses used in animal studies on a per-kg basis. Whether human supplementation achieves the intracellular concentration needed to meaningfully activate autophagy is debated.
Evidence Strength: Mechanistically Compelling / Human Data Early
More interesting than resveratrol from a human evidence standpoint, but earlier-stage than berberine. The autophagy mechanism is among the most robust longevity pathways identified. If the human evidence matures as the animal data suggests, spermidine may become a primary intervention.
5. Quercetin and Fisetin (Senolytics)
The Mechanism
Cellular senescence is one of the hallmarks of ageing. Senescent cells are cells that have stopped dividing but resist apoptosis (programmed death). They accumulate with age and release an inflammatory cocktail called the SASP (senescence-associated secretory phenotype) that drives chronic inflammation, tissue damage, and promotes senescence in neighbouring cells.
Senolytics are compounds that selectively kill senescent cells. The first clinically validated senolytic combination is Dasatinib + Quercetin (D+Q), studied by the Mayo Clinic and others.
Fisetin (a flavonoid from strawberries, apples, and other foods) has also shown senolytic activity in animal studies and is being studied in humans (AFFIRM-LITE trial, Mayo Clinic).
Evidence
Animal evidence: Dramatic. Senolytic treatment in mice extends lifespan, improves physical function in aged animals, and reduces multiple age-related conditions.
Human evidence: Early but real. D+Q has shown reduction of senescent cell burden in human adipose tissue in a small clinical trial. Fisetin human trials are ongoing.
The protocol: Unlike most longevity supplements taken daily, senolytics are taken in "pulses" — high-dose, short-duration courses — rather than chronic daily supplementation. This mimics the intermittent treatment approach used in clinical trials.
Dosing (Fisetin)
Pulse protocol: 20mg/kg per day for 2 days, repeated monthly or quarterly. For an 80kg man: 1,600mg fisetin on day 1 and 2.
This is significantly higher than typical antioxidant supplementation doses for fisetin (100–500mg/day for general health). The senolytic effect appears to require this higher pulsed approach.
Daily supplementation: Lower doses (100–200mg/day) for general anti-inflammatory and cognitive effects. The senolytic claim at these doses is not established.
Evidence Strength: Animal = Very Strong / Human = Promising but Early
The most exciting mechanistic area in longevity science. The translational potential is high. The human evidence for meaningful healthspan extension is not yet established. Worth following and worth the low-risk supplementation given the safety profile.
6. Rapamycin (Off-Label) — For Reference Only
Rapamycin (sirolimus) is the most consistently life-extending compound across multiple species tested to date. It inhibits mTOR (mechanistic target of rapamycin), the nutrient-sensing kinase that drives cellular growth and is associated with accelerated ageing when chronically activated.
Rapamycin extends mean lifespan in mice by 10–25% even when started late in life. It is an FDA-approved immunosuppressant for organ transplants.
Used off-label in very small doses (2–6mg once weekly, pulsed dosing to avoid immunosuppression) by a subset of longevity-focused physicians and their patients. This is cutting-edge, medically controversial, and requires physician oversight.
Not a supplement to self-administer. Included here for reference because MPMD-style content covers it, and it is increasingly discussed in longevity circles. UK access is only through specialist private physicians.
7. The Full Stack: Practical Implementation
Core Longevity Protocol (Well-Supported)
Morning (with fat-containing food):
- NMN 500mg (or NR 500mg)
- Resveratrol or Pterostilbene 500mg
- Berberine 500mg
Afternoon (with food):
- Berberine 500mg
Evening (with food):
- Berberine 500mg
Daily additions (covered in supplements guide):
- Vitamin D3 + K2
- Magnesium glycinate (before bed)
- Omega-3 EPA+DHA 2–3g
- Zinc 15–25mg
Monthly pulse:
- Fisetin 20mg/kg for 2 consecutive days (senolytic protocol)
Cost (UK, Monthly)
| Compound | Monthly Cost | |----------|-------------| | NMN 500mg/day | £25–45 (UK suppliers) | | Pterostilbene 500mg/day | £15–20 | | Berberine 1500mg/day | £15–20 | | Fisetin (monthly pulse) | £8–12 | | Spermidine 1mg/day | £15–25 | | Total | £78–122/month |
This is on top of the foundational supplements (D3, magnesium, omega-3, zinc) which add approximately £40–60/month.
Who This Stack Is For
Men over 40 who are serious about longevity optimisation, have already established the foundations (sleep, body composition, testosterone, fundamentals), and want to implement the most current evidence-based additional interventions.
This is not a beginner protocol. It adds meaningful complexity and cost. The evidence quality varies from strong (berberine metabolic effects) to promising-but-early (spermidine, fisetin). Know which is which before spending money.
UK Sources
NMN/NR: Tru Niagen (NR, UK-available), Double Wood Supplements (Amazon UK), Elysium Basis (subscription model).
Berberine: Bulk, Nutricost, Pure Encapsulations (all available Amazon UK or direct).
Pterostilbene: Double Wood Supplements, Nootropics Depot (Amazon UK).
Fisetin: Double Wood Supplements, Life Extension (iHerb UK delivery).
Spermidine: Available as wheat germ extract supplements — Primeadine (premium), or generic wheat germ spermidine supplements.
The Short Version
The longevity stack targets cellular ageing mechanisms: NAD+ decline (NMN/NR), sirtuin activation (resveratrol/pterostilbene), AMPK/autophagy (berberine), autophagy induction (spermidine), and senescent cell clearance (fisetin). Berberine has the strongest human metabolic evidence. NMN/NR have solid NAD+ elevation data. Resveratrol disappoints on human outcomes but pterostilbene bioavailability is better. Fisetin and spermidine are the most exciting early-stage compounds. Implement foundations first. Build this stack systematically once they're solid.
Where to Buy
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