Klotho

Full-length alpha-Klotho is a 1012-amino-acid, roughly 130 kDa transmembrane protein expressed mainly in kidney and choroid plexus, where it serves as the co-receptor that makes FGF23 signalling possible and thereby governs phosphate handling. The longevity biology, however, belongs to the shed soluble ectodomain circulating in blood and CSF. Soluble klotho dampens insulin/IGF-1 signalling, inhibits Wnt and TGF-beta, suppresses oxidative stress via FoxO, and enhances NMDA receptor subunit trafficking at the synapse. Klotho-deficient mice show accelerated ageing across nearly every tissue; over-expressing mice live longer. In 2023, a single low subcutaneous dose of soluble klotho improved memory in aged rhesus monkeys, which is the single most compelling piece of translational evidence in this class. Delivery remains the unsolved problem — this is a large glycoprotein, not a peptide, and it does not survive casual handling.

Targets: FGF23 / FGFR co-receptor complex, Insulin/IGF-1 signalling, NMDA receptor subunit GluN2B, Wnt and TGF-beta signalling

• · Research-grade klotho is sold in microgram quantities, not milligrams, and what is in those vials is usually a fragment or a recombinant construct rather than the full soluble ectodomain used in the primate studies. There is no validated human dose, and the low-dose primate result specifically did not scale — the higher dose did not work better.

Work out your exact syringe units →

• commonUnknown in humans— No human administration study has reported a safety profile.
• uncommonPhosphate and mineral metabolism disturbance— Theoretical but mechanistically real — klotho sits at the centre of FGF23-driven phosphate handling.
• uncommonImmunogenicity to a recombinant protein— Any injected large recombinant protein carries anti-drug antibody risk.

• Chronic kidney disease or disordered mineral metabolism — this protein directly governs phosphate handling and the consequences of perturbing it are not trivial.
• Pregnancy and breastfeeding — no data.

• cautionvitamin-d — Klotho-FGF23 signalling suppresses 1,25-dihydroxyvitamin D production; high-dose vitamin D and klotho pull mineral metabolism in opposing directions.

• · Serum phosphate, calcium and PTH if you are administering anything claiming to be klotho.
• · Renal function panel.
• · Serum klotho assays exist but are notoriously inconsistent between platforms and are not useful for tracking dosing.

Not approved anywhere. Sold as a research reagent; clinical programmes (mRNA and gene therapy approaches) are in early phase trials.

• Kuro-o et al. 1997, Nature — mutation of the mouse klotho gene leads to a syndrome resembling ageing (preclinical)
• Castner et al. 2023, Nature Aging — longevity factor klotho enhances cognition in aged nonhuman primates (preclinical)
• Review of soluble klotho mechanisms and therapeutic potential (review)

Klotho has two jobs that people constantly conflate. As a membrane protein in kidney and choroid plexus, it is the obligate co-receptor that makes FGF23 signalling possible through FGF receptors, and that axis governs phosphate handling and 1,25-dihydroxyvitamin D production. That is the endocrine job and it is why klotho-deficient animals develop hyperphosphataemia and a phenotype that reads as accelerated ageing across nearly every tissue — the Kuro-o 1997 Nature paper described short lifespan, infertility, arteriosclerosis, skin atrophy, osteoporosis and emphysema in a single mutant. The longevity biology, though, belongs to the shed soluble ectodomain circulating in blood and CSF, and it acts as a hormone in its own right: dampening insulin/IGF-1 signalling, inhibiting Wnt and TGF-beta, suppressing oxidative stress through FoxO, and enhancing NMDA receptor GluN2B subunit trafficking at the synapse. The 2023 Castner result in Nature Aging is the translational headline — a single low subcutaneous dose of soluble klotho improved spatial and working memory in aged rhesus monkeys, and the effect lasted at least two weeks. The mechanistic follow-up from the same group in the same year is arguably more important for anyone thinking about buying klotho: Park and colleagues showed that klotho acts on the brain indirectly, by inducing platelet factor 4, which is what actually crosses into the brain and enhances synaptic plasticity. Klotho itself is a 130 kDa glycoprotein and does not cross the blood-brain barrier. That reframes the whole compound — it is a peripheral signal that triggers a second messenger, not a neuroactive agent. It also explains why the dose-response was non-monotonic: the low dose worked in aged monkeys and the high dose did not, which is the opposite of how people instinctively dose things.

The dominant failure is product identity, and it is worse here than anywhere else on this page. Klotho is a 1012-residue glycoprotein of roughly 130 kDa. It is not a peptide, it is fragile, its glycosylation matters for function, and it does not survive the casual handling that a four-residue peptide shrugs off. Research-grade klotho is sold in microgram quantities, is often a fragment or a truncated recombinant construct, and is frequently produced in expression systems that do not glycosylate the way human cells do. The probability that what is in your vial is the molecule that worked in the monkey study is low, and no amount of careful dosing fixes that. The second failure is dosing upward. The primate study found the low dose effective and the high dose not — the dose-response is non-monotonic. Escalating because you felt nothing is the exact wrong response and it is what people instinctively do. The third is mineral metabolism. This protein governs phosphate handling, and people take it without ever checking a phosphate level. In anyone with reduced kidney function that is a genuinely bad idea rather than a cautious one. The fourth is expecting a brain effect from a molecule that does not enter the brain — the cognitive effect in the primate work is relayed through platelet factor 4, which means it depends on an intact peripheral signalling chain rather than on getting klotho past the blood-brain barrier. The fifth is immunogenicity: any injected large recombinant protein can raise anti-drug antibodies, and with an unregulated product you have no idea what else is in the vial to react to.

• FGF23 / FGFR1c co-receptor complex — Klotho is an obligate co-receptor rather than a ligand; the complex is required for FGF23 to signal at physiological concentrations.

  Governs renal phosphate excretion and suppresses 1,25-dihydroxyvitamin D synthesis. This is the endocrine arm and the source of the mineral-metabolism risk.

• NMDA receptor GluN2B subunit — Not a direct receptor interaction — klotho enhances subunit trafficking rather than binding the channel.

  Increased synaptic GluN2B, enhanced synaptic plasticity and cognitive performance. Demonstrated to be GluN2B-dependent in transgenic mouse work including an alpha-synuclein model.

• Platelet factor 4 (PF4) induction — Downstream induction, not binding.

  This is the crucial one. Klotho induces PF4, and PF4 is what permeates the brain and enhances synaptic plasticity and cognition. Klotho itself does not cross the blood-brain barrier — the cognitive effect is relayed.

• Insulin / IGF-1 signalling — Not characterised as a binding interaction.

  Dampened insulin/IGF-1 signalling, which is the canonical longevity axis and the mechanistic link to lifespan extension in klotho-overexpressing mice.

• Wnt and TGF-beta signalling — Direct binding to Wnt ligands has been reported.

  Inhibition of Wnt (limiting stem cell exhaustion) and TGF-beta (limiting fibrosis). Central to the anti-fibrotic renal effects.

In aged rhesus macaques, memory improvement after a single low subcutaneous dose was measurable within hours to days and persisted for around two weeks. That is the only administered-klotho time course that exists in a primate, and it is unusual enough to be worth stating plainly: this is a single-dose, long-duration, non-monotonic pharmacology, not a daily-dosing compound. In humans nothing has been administered in a published study, so there is no human onset timeline. The mineral-metabolism effects, if they occur, would be expected within days and would be visible on a phosphate level long before you felt anything.

The interaction that matters is with vitamin D, and it is a real mechanistic conflict rather than a theoretical one. Klotho-FGF23 signalling suppresses 1,25-dihydroxyvitamin D production and drives phosphate excretion; high-dose vitamin D increases calcium and phosphate absorption. They pull mineral metabolism in opposite directions, and if you are running high-dose vitamin D — which a large fraction of this audience is — you should have phosphate, calcium and PTH numbers before adding anything klotho-related. The same caution extends to phosphate binders, calcium supplementation and anything else touching bone-mineral metabolism. Beyond that, klotho is usually stacked with the rest of the longevity shelf on general principle, and there is no evidence for or against any of those combinations. The bigger practical issue is that the stacking question is largely moot: what is sold as klotho on the research market is usually a fragment or a recombinant construct rather than the intact glycosylated soluble ectodomain used in the primate work, so you are frequently stacking an unknown.

Against everything else on this page, klotho has the most impressive underlying biology and the worst practical situation. The genetics in mice are outstanding — knock it out and the animal ages catastrophically, overexpress it and it lives longer. The primate cognition result is the strongest single translational finding in this class. The human evidence is entirely genetic and observational: KL-VS carriers do better on cognition and neurodegeneration biomarkers. And the thing you can actually buy is probably not the molecule that produced any of that. Against SS-31, which is an approved drug with a label: no comparison. Against exercise: the Jarchow 2025 result showing fitness and klotho genotype interacting favourably is a reminder that exercise raises endogenous klotho and is free. Against the clinical pipeline: mRNA and gene therapy approaches to raising klotho are entering early trials, and those — not a vial of recombinant protein — are the routes by which klotho is likely to become a real intervention. The honest position on klotho today is that it is the most exciting target in longevity biology and one of the worst things on this list to actually buy.

Not meaningfully estimable and deliberately left null. Recombinant klotho is sold as a research reagent by mass in micrograms at reagent pricing, there is no established human dose, and the primate work used material produced to a standard that research-market product is unlikely to match. Any monthly figure would imply a protocol that does not exist and a product identity that cannot be assumed.

• ?No human clinical trial of administered klotho protein exists. I searched for one specifically and found none.
• ?No pharmacokinetic data exist for administered klotho in any species.
• ?There is no validated human dose. The primate low dose has not been scaled or tested in people.
• ?The identity and integrity of research-market klotho is unverifiable by the buyer, and it is unlikely to match the material used in the primate study.
• ?The blood-brain barrier field is set to 'no' based on the Park 2023 PF4 relay mechanism; whether any fraction of soluble klotho crosses under any circumstances was not something I could definitively resolve.
• ?The molecular weight is not stated in the Core record and I did not resolve an authoritative figure; the ~130 kDa value is the commonly cited one and is approximate for a glycoprotein whose mass depends on glycosylation.
• ?The non-monotonic dose-response was observed in one primate study and the mechanism behind it is not explained.
• ?How long the endogenous soluble klotho half-life is in humans was not resolved.
• ?Serum klotho assay variability is well known but I did not resolve a quantitative between-platform comparison.
• ?Cost cannot be estimated because neither dose nor product identity is established.

• Mutation of the mouse klotho gene leads to a syndrome resembling ageing Kuro-o M, Matsumura Y, Aizawa H, Kawaguchi H, Suga T, Utsugi T, Ohyama Y, Kurabayashi M, Kaname T, Kume E, Iwasaki H, Iida A, Shiraki-Iida T, Nishikawa S, Nagai R, Nabeshima YI, Nature, 1997 · PMID 9363890

  The founding paper. Klotho deficiency produces short lifespan, infertility, arteriosclerosis, skin atrophy, osteoporosis and emphysema in mice. This is why klotho is called the anti-ageing gene, and it is a loss-of-function result, which is a weaker basis for supplementation than people assume.

• Longevity factor klotho enhances cognition in aged nonhuman primates Castner SA, Gupta S, Wang D, Moreno AJ, Park C, Chen C, Poon Y, Groen A, Greenberg K, David N, Boone T, Baxter MG, Williams GV, Dubal DB, Nature Aging, 2023 · PMID 37400721

  The single most compelling translational result in this class — a single low subcutaneous dose of klotho improved spatial and working memory in aged rhesus macaques. Note the non-monotonic dose-response: low dose worked, high dose did not.

• Platelet factors are induced by longevity factor klotho and enhance cognition in young and aging mice Park C, Hahn O, Gupta S, Moreno AJ, Marino F, Kedir B, et al., Nature Aging, 2023 · PMID 37587231

  The mechanistic key. Klotho works on the brain indirectly by inducing platelet factor 4, which is what actually reaches the brain. Klotho itself does not cross the blood-brain barrier, and this paper is the reason the BBB field in this record reads 'no'.

• Longevity factor klotho and resistance to cognitive deficits in individuals with Parkinson's disease and in an alpha-synuclein mouse model Luthra NS, Bonham LW, Moreno AJ, et al., Journal of Neuroscience, 2026 · PMID 41916755

  Human genetic association (the KL-VS variant and preserved executive cognition in Parkinson's disease) paired with a mouse model showing the effect is GluN2B-dependent. Good example of the human evidence for klotho being genetic rather than interventional.

• KLOTHO KL-VS heterozygosity is associated with diminished age-related neuroinflammation, neurodegeneration, and synaptic dysfunction in older cognitively unimpaired adults Driscoll IF, Lose S, Ma Y, et al., Alzheimer's & Dementia, 2024 · PMID 39030746

  CSF biomarker evidence in humans that carrying the favourable klotho variant attenuates age-related neuroinflammation and synaptic dysfunction. This is the shape of the human klotho evidence — genetic, observational, and about lifelong exposure rather than an injection.

• More fit KL-VS heterozygotes have more favorable AD-relevant biomarker profiles Jarchow M, Driscoll I, Breidenbach BM, et al., Alzheimer's & Dementia (New York), 2025 · PMID 40787159

  Cardiorespiratory fitness and klotho genotype interact on neurodegeneration biomarkers. Practically relevant because it is the one klotho-related intervention available to you today that has human evidence behind it, and it is exercise.