The Science of Aging: Telomeres, Senescent Cells, and the Race to Slow Your Death Clock

The 60-second version

Ageing is not a single process. It is at least nine interconnected biological mechanisms that erode your body's ability to maintain itself. Since 2013, scientists have had a formal framework for these mechanisms, called the hallmarks of ageing, and every serious anti-ageing intervention targets one or more of them.

This article is a comprehensive audit of every major anti-ageing pathway currently under investigation. For each one, we present the mechanism, the animal evidence, the human evidence (or lack thereof), and an honest assessment of where things stand. The longevity field is plagued by hype, conflicts of interest, and supplement salesmen masquerading as scientists. We are going to cut through all of it.

The 9 hallmarks of ageing (and why they matter)

In 2013, Carlos Lopez-Otin and colleagues published a landmark paper in Cell that proposed nine hallmarks of ageing, a framework that has since become the organising principle for the entire field of geroscience. The paper has been cited over 15,000 times. In January 2023, the same group updated the framework to include three additional hallmarks, bringing the total to twelve. Understanding these hallmarks is essential because every intervention discussed in this article targets one or more of them.

1. Genomic instability

Your DNA sustains tens of thousands of lesions every single day. Ultraviolet radiation, reactive oxygen species, replication errors, and spontaneous depurination all damage the genome. Young cells repair this damage efficiently through an arsenal of repair pathways including base excision repair, nucleotide excision repair, mismatch repair, and homologous recombination. As you age, these repair mechanisms become less efficient. Errors accumulate. Mutations pile up. Some of these mutations will be in tumour suppressor genes or oncogenes, and that is when cancer begins.

Progeroid syndromes, those rare genetic diseases where children age at terrifying speed, almost always involve defects in DNA repair. Werner syndrome, Cockayne syndrome, and xeroderma pigmentosum all produce accelerated ageing because the genome cannot maintain its integrity. This tells us something profound: genomic instability is not merely correlated with ageing. It is causally linked to it.

2. Telomere attrition

Telomeres are repetitive DNA sequences (TTAGGG in humans, repeated roughly 2,500 times) that cap the ends of chromosomes. Each time a cell divides, the telomeres shorten slightly because DNA polymerase cannot fully replicate the 3-prime end of linear chromosomes. This is called the end-replication problem. When telomeres become critically short, the cell enters replicative senescence or triggers apoptosis. We will explore telomere biology in enormous detail in the next section.

3. Epigenetic alterations

Your epigenome is the collection of chemical modifications to DNA and histone proteins that determine which genes are turned on or off in any given cell. DNA methylation, histone acetylation, histone methylation, and chromatin remodelling all play roles. As you age, your epigenome drifts. Regions that should be silenced become active. Regions that should be active become silenced. This epigenetic drift is so predictable that researchers have built clocks from it, allowing them to estimate biological age from a blood sample with remarkable accuracy. We cover these clocks in detail below.

4. Loss of proteostasis

Proteins must be correctly folded to function. Your cells maintain protein quality through chaperone proteins (which assist folding), the ubiquitin-proteasome system (which degrades misfolded proteins), and autophagy (which clears larger protein aggregates and damaged organelles). With age, all three systems decline. Misfolded proteins accumulate. In the brain, this manifests as amyloid-beta plaques in Alzheimer's disease, alpha-synuclein aggregates in Parkinson's disease, and tau tangles in multiple neurodegenerative conditions. Proteostasis failure is arguably the hallmark most directly responsible for neurodegeneration.

5. Deregulated nutrient sensing

Four interconnected nutrient-sensing pathways play central roles in ageing: the insulin/IGF-1 signalling pathway, mTOR (mechanistic target of rapamycin), AMPK (AMP-activated protein kinase), and sirtuins. In youth, these pathways balance growth and repair appropriately. With age, the balance shifts towards chronic growth signalling, which promotes cell proliferation at the expense of maintenance and repair. This is why interventions that mimic nutrient scarcity, such as caloric restriction, rapamycin, and metformin, consistently extend lifespan in animal models. They dial down growth signalling and dial up cellular maintenance.

6. Mitochondrial dysfunction

Mitochondria are the power plants of the cell, generating ATP through oxidative phosphorylation. With age, mitochondrial function declines. The electron transport chain becomes leaky, producing more reactive oxygen species (ROS). Mitochondrial DNA, which lacks the protective histones and sophisticated repair mechanisms of nuclear DNA, accumulates mutations. The result is an energy crisis at the cellular level: cells produce less ATP, generate more oxidative stress, and trigger inflammatory signalling. Mitochondrial dysfunction is particularly devastating in energy-hungry tissues like the brain, heart, and skeletal muscle.

7. Cellular senescence

When cells accumulate too much damage to safely divide, they enter a state of permanent growth arrest called senescence. This is initially protective because it prevents damaged cells from becoming cancerous. But senescent cells do not quietly retire. They secrete a toxic cocktail of inflammatory cytokines, growth factors, and matrix metalloproteinases called the senescence-associated secretory phenotype (SASP). This SASP damages neighbouring healthy cells, promotes inflammation, and can paradoxically promote cancer in surrounding tissue. Clearing these zombie cells is one of the most promising avenues in geroscience. We dedicate an entire section to senolytics below.

8. Stem cell exhaustion

Your body's ability to regenerate depends on tissue-resident stem cells. Haematopoietic stem cells replenish your blood. Satellite cells repair your muscles. Intestinal stem cells replace your gut lining every few days. With age, these stem cell pools shrink, accumulate DNA damage, and become less functional. The decline in stem cell function explains why wounds heal more slowly in elderly people, why muscle mass is lost despite exercise, and why the immune system weakens with age. Stem cell exhaustion is both a consequence and a driver of the other hallmarks.

9. Altered intercellular communication

Ageing changes how cells communicate with each other. The most significant change is a chronic, low-grade inflammation that gerontologists call "inflammaging." Pro-inflammatory cytokines like IL-6, TNF-alpha, and IL-1-beta are chronically elevated in aged tissues. This systemic inflammation drives atherosclerosis, neurodegeneration, insulin resistance, and cancer. The source of inflammaging is multifactorial: senescent cells contribute through SASP, the gut microbiome changes, immune surveillance declines, and visceral fat expands. Controlling inflammaging is a central goal of anti-ageing medicine.

The 2023 update: three new hallmarks

In 2023, Lopez-Otin expanded the framework to include three additional hallmarks: disabled macroautophagy (the decline of the cellular recycling system), chronic inflammation (elevated from a feature of altered intercellular communication to its own hallmark), and dysbiosis (age-related disruption of the gut microbiome). The addition of dysbiosis was particularly notable, as it reflected growing evidence that the composition and diversity of gut bacteria changes dramatically with age and contributes to systemic inflammation, metabolic dysfunction, and even neurodegeneration through the gut-brain axis.

Telomeres: the cellular countdown timer

Telomere biology is perhaps the most publicly recognisable branch of ageing science, largely because of the 2009 Nobel Prize in Physiology or Medicine awarded to Elizabeth Blackburn, Carol Greider, and Jack Szostak for their discovery of how telomeres and the enzyme telomerase protect chromosomes. Their work, which began with studies on Tetrahymena (a pond-dwelling protozoan), fundamentally changed our understanding of cellular ageing.

What telomeres actually do

Telomeres solve a structural problem. The ends of linear chromosomes resemble broken DNA, and without a protective cap, the cell's DNA repair machinery would treat them as damage, attempting to fuse chromosome ends together or triggering apoptosis. Telomeric DNA, bound by a six-protein complex called shelterin, forms a loop structure (the T-loop) that hides the chromosome end from these repair systems.

At birth, human telomeres are approximately 10,000 to 15,000 base pairs long. They shorten by roughly 20 to 50 base pairs per cell division. When they reach a critical length of around 4,000 to 6,000 base pairs, the shelterin complex can no longer form the protective T-loop. The exposed chromosome end triggers a DNA damage response, and the cell either enters senescence or undergoes apoptosis.

Telomerase: the enzyme that rebuilds telomeres

Telomerase is a reverse transcriptase enzyme that can add telomeric repeats back onto chromosome ends, counteracting the shortening that occurs with each division. In humans, telomerase is highly active in germ cells (ensuring that each generation starts with long telomeres), stem cells (allowing them to divide extensively), and, problematically, in about 85-90% of cancers (allowing them to divide indefinitely). Most somatic cells express little or no telomerase, which is why telomere shortening acts as a biological clock limiting cell division.

This creates a fundamental tension in anti-ageing medicine: lengthening telomeres could rejuvenate ageing cells, but it could also promote cancer by removing a key brake on cell proliferation. This tension is not theoretical. Mice engineered to overexpress telomerase develop more tumours, although when combined with extra copies of tumour suppressor genes (p53, p16, and p19ARF), they live 40% longer than normal mice without increased cancer risk (Tomas-Loba et al., 2008, Cell).

Telomere length and mortality: the epidemiological evidence

The largest study linking telomere length to mortality is the Copenhagen General Population Study, published by Rode et al. in 2015. This prospective study measured leukocyte telomere length in 64,637 individuals from the Danish general population and followed them for mortality outcomes. The findings were striking: individuals in the shortest telomere length decile had a 23% higher risk of all-cause mortality compared to those in the longest decile, after adjustment for age, sex, and other risk factors. The association held across multiple causes of death, including cardiovascular disease and cancer.

However, the relationship is not as straightforward as popular science reporting suggests. A 2017 meta-analysis by Haycock et al. in the BMJ, covering 25 studies and over 121,000 participants, found that the association between telomere length and mortality was modest (hazard ratio of 1.09 per standard deviation decrease in telomere length) and weakened substantially after adjusting for potential confounders. Telomere length explains only a small fraction of the variation in human lifespan, and it is a far weaker predictor than conventional risk factors like smoking status, blood pressure, and BMI.

What affects telomere length?

Multiple lifestyle and environmental factors influence the rate of telomere attrition:

• Smoking: Accelerates telomere shortening by approximately 25-27 additional base pairs per year, equivalent to about 4.6 years of additional biological ageing per pack-year (Valdes et al., 2005).
• Obesity: BMI above 30 is associated with significantly shorter telomeres. Valdes et al. found that obesity was equivalent to approximately 8.8 years of additional telomere ageing.
• Exercise: Regular moderate exercise is associated with longer telomeres. A 2015 study by Tucker found that adults who exercised at high levels had telomeres corresponding to 9 years of reduced biological ageing compared to sedentary adults.
• Chronic psychological stress: Blackburn's collaboration with psychologist Elissa Epel demonstrated that mothers caring for chronically ill children had shorter telomeres and lower telomerase activity than controls, corresponding to 9 to 17 years of additional ageing (Epel et al., 2004, PNAS).
• Sleep: Short sleep duration (under 6 hours) is associated with shorter telomeres, particularly in older adults (Cribbet et al., 2014).
• Diet: Mediterranean diet adherence is associated with longer telomeres in multiple studies, potentially mediated through reduced oxidative stress and inflammation (Crous-Bou et al., 2014, BMJ).

Can you lengthen your telomeres?

Lifestyle interventions can slow telomere attrition and may modestly lengthen telomeres. Dean Ornish's 2013 pilot study in The Lancet Oncology reported a 10% increase in telomere length over 5 years in a small group (n=10) following a comprehensive lifestyle programme (plant-based diet, exercise, stress management, and social support), compared to a 3% decrease in the control group. However, the sample size was tiny, and the findings have not been replicated at scale.

Pharmaceutical telomere lengthening is not yet available for clinical use. TA-65, a supplement derived from astragalus root that purportedly activates telomerase, has been marketed aggressively since the mid-2000s. A 2011 study by Harley et al. showed modest telomerase activation in cell culture, but human clinical evidence for meaningful telomere lengthening or health benefits remains weak and largely confined to company-sponsored research.

Epigenetic clocks: measuring your real age

If telomeres are a crude speedometer, epigenetic clocks are a precision instrument. The development of DNA methylation-based age estimators has been one of the most transformative advances in geroscience, giving researchers (and individuals) the ability to measure biological age with remarkable accuracy.

How epigenetic clocks work

DNA methylation is a chemical modification where a methyl group is added to a cytosine base, typically at CpG dinucleotides (positions where cytosine is followed by guanine). The human genome contains roughly 28 million CpG sites, and the methylation pattern at these sites changes predictably with age. Some sites gain methylation over time; others lose it. By measuring the methylation status at carefully selected CpG sites, researchers can estimate chronological age with a median error of less than 3.6 years.

The major clocks

Horvath clock (2013)

Steve Horvath's multi-tissue clock was the breakthrough. Published in Genome Biology, it uses 353 CpG sites measured across 51 different tissues and cell types to estimate chronological age. The clock works in virtually every tissue in the body, from blood to brain to liver, with a correlation of 0.96 between estimated and chronological age. When your Horvath age exceeds your chronological age, you are biologically older than your birth certificate suggests. Multiple studies have shown that epigenetic age acceleration (the gap between biological and chronological age) predicts all-cause mortality, cardiovascular disease, cancer incidence, and cognitive decline.

GrimAge (2019)

Developed by Ake Lu, Austin Quach, and Steve Horvath, GrimAge is a second-generation clock designed specifically to predict mortality rather than merely estimate chronological age. It incorporates DNA methylation surrogates for seven plasma proteins (including PAI-1 and GDF-15, both strong predictors of death) and smoking pack-years. GrimAge is arguably the best current predictor of remaining lifespan and has been validated in multiple independent cohorts. A 2019 analysis showed that each one-year increase in GrimAge acceleration was associated with a 10% increase in all-cause mortality risk.

DunedinPACE (2022)

DunedinPACE (Pace of Aging Computed from the Epigenome) takes a fundamentally different approach. Rather than estimating your biological age at a single point in time, it estimates the rate at which you are ageing. Developed using longitudinal data from the Dunedin Study, a birth cohort of 1,037 individuals tracked from birth to their mid-40s, DunedinPACE uses 173 CpG sites to estimate whether you are ageing faster or slower than average. A DunedinPACE score of 1.0 means you are ageing at the expected rate; 1.2 means you are ageing 20% faster than average; 0.8 means 20% slower. This approach is particularly useful for evaluating interventions because it can detect changes in the pace of ageing over relatively short time periods.

What accelerates epigenetic ageing?

The same factors that damage health generally also accelerate epigenetic ageing, which serves as a validation that these clocks are measuring something biologically meaningful:

• Smoking: The single largest accelerator of epigenetic age, adding 2 to 7 years of biological age depending on cumulative exposure.
• Obesity: Higher BMI is consistently associated with epigenetic age acceleration, particularly in liver tissue.
• Chronic stress and adverse childhood experiences: Multiple studies have linked childhood trauma to accelerated epigenetic ageing in adulthood.
• Poor sleep: Shift workers and those with chronically disrupted sleep show accelerated epigenetic ageing.
• Air pollution: Particulate matter exposure (PM2.5) is associated with faster biological ageing as measured by several clocks.
• HIV infection: Even with effective antiretroviral therapy, HIV infection accelerates epigenetic ageing by approximately 2 to 5 years.
• Heavy alcohol use: Accelerates multiple epigenetic clocks, with a dose-response relationship.

Conversely, exercise, Mediterranean diet adherence, and higher educational attainment are associated with slower epigenetic ageing. A 2023 study by Fitzgerald et al. in the journal Aging demonstrated that an 8-week programme combining diet (high in folate, betaine, and polyphenols), exercise, sleep optimisation, and stress reduction slowed DunedinPACE by approximately 3% compared to controls. The effect was modest but statistically significant, suggesting that lifestyle interventions can measurably slow the pace of biological ageing.

Senescent cells: the zombie apocalypse inside you

If you had to bet on which area of geroscience will produce the first genuine anti-ageing therapy, senescent cell clearance (senolytics) would be a strong contender. The science is compelling, the animal data is dramatic, and multiple human trials are underway.

What are senescent cells?

Cellular senescence was first described by Leonard Hayflick in 1961 when he observed that human fibroblasts could only divide a limited number of times before entering permanent growth arrest (the Hayflick limit). We now know that senescence can be triggered by multiple stimuli beyond replicative exhaustion: oncogene activation, DNA damage, oxidative stress, mitochondrial dysfunction, and telomere attrition.

A senescent cell is alive but will never divide again. It resists apoptosis (programmed cell death) through upregulation of anti-apoptotic pathways, including the BCL-2 family of proteins. Most importantly, it secretes the senescence-associated secretory phenotype (SASP), a complex mixture of over 100 pro-inflammatory cytokines, chemokines, growth factors, and matrix-degrading enzymes. The SASP includes IL-6, IL-8, MCP-1, PAI-1, VEGF, and multiple matrix metalloproteinases.

Young bodies contain very few senescent cells. In a 20-year-old, perhaps 1 in 10,000 cells is senescent. By age 60, estimates range from 1 in 100 to 1 in 30 in some tissues. This accumulation is exponential, and it drives a disproportionate amount of age-related dysfunction because each senescent cell poisons its neighbours through SASP.

The Baker mouse experiments

The landmark study that electrified the field was published by Darren Baker and Jan van Deursen at the Mayo Clinic in 2016 in Nature. They engineered mice with a genetic kill switch (the INK-ATTAC transgene) that allowed selective elimination of senescent cells expressing p16Ink4a. When senescent cells were cleared starting at middle age, the results were remarkable: median lifespan increased by 17 to 35% depending on the genetic background. Treated mice showed reduced tumour incidence, better kidney and heart function, increased fat tissue functionality, and delayed onset of cataracts. The mice were not just living longer; they were healthier for a greater proportion of their lives.

A critical follow-up study by the same group demonstrated that transplanting senescent cells into young mice was sufficient to cause physical dysfunction and reduced lifespan, proving that senescent cells are not merely markers of ageing but active drivers of it. Just 500,000 transplanted senescent cells (a tiny fraction of total body cells) caused measurable physical decline within weeks.

Senolytics: drugs that kill zombie cells

Senolytics are drugs that selectively destroy senescent cells while sparing healthy cells. The first senolytic combination identified was dasatinib (a cancer drug) plus quercetin (a plant flavonoid), discovered by James Kirkland's group at Mayo Clinic. Dasatinib targets senescent pre-adipocytes and endothelial cells, while quercetin targets senescent fibroblasts and epithelial cells. Together, they cover a broad range of senescent cell types.

In mice, dasatinib plus quercetin improved cardiovascular function, enhanced exercise capacity, reduced osteoporosis, extended healthspan, and increased median lifespan by approximately 36% when treatment began at the equivalent of age 75 in humans. Crucially, the drugs only needed to be given intermittently (a short course every two weeks), because once senescent cells are cleared, they take time to reaccumulate.

Human trials: where we stand

The first human trial of senolytics was published in 2019 by Justice et al. in EBioMedicine. Fourteen patients with idiopathic pulmonary fibrosis received three days of dasatinib (100mg/day) plus quercetin (1250mg/day) per week for three weeks. Physical function improved modestly, with statistically significant gains in 6-minute walk distance and chair-stand test performance. However, the study had no control group and was primarily a safety and feasibility trial.

Larger trials are underway. A phase 2 trial of dasatinib plus quercetin for Alzheimer's disease (the SToMP-AD trial) began enrolling in 2020 and reported early results showing that the combination was safe and well-tolerated in older adults with mild cognitive impairment. An NIH-funded trial is testing senolytics in diabetic kidney disease. Multiple other trials are evaluating senolytics for osteoarthritis, frailty, and bone marrow transplant survivors.

Unity Biotechnology, a senolytic drug company founded in 2011 and backed by Jeff Bezos and Peter Thiel, had a high-profile setback in 2020 when its lead compound UBX0101 (an MDM2 inhibitor targeting senescent cells in joints) failed a phase 2 trial for osteoarthritis of the knee. The drug showed no significant benefit over placebo on pain or function endpoints. This failure led to a 60% drop in Unity's share price and raised questions about whether the senolytic approach would translate from mice to humans. However, Unity pivoted to ophthalmology, and its UBX1325 compound (now called foselutoclax) showed more promising results in phase 2 trials for diabetic macular oedema and wet age-related macular degeneration.

The mTOR pathway and rapamycin

If there is a single molecule that sits at the centre of ageing biology, it is mTOR (mechanistic target of rapamycin). mTOR is a serine/threonine kinase that integrates signals from nutrients, growth factors, energy status, and stress to determine whether a cell should grow and proliferate or enter a state of maintenance and repair. When nutrients are abundant, mTOR is active and promotes protein synthesis, cell growth, and suppression of autophagy. When nutrients are scarce, mTOR is inhibited, and the cell switches to survival mode: degrading damaged components, recycling cellular waste, and conserving energy.

Rapamycin: the most validated anti-ageing drug in animals

Rapamycin (also known as sirolimus) was originally discovered in a soil sample from Easter Island (Rapa Nui) in 1972 and is approved by the FDA as an immunosuppressant for organ transplant recipients and as a cancer drug. It inhibits mTOR complex 1 (mTORC1), effectively mimicking the cellular effects of caloric restriction.

The Interventions Testing Program (ITP), a rigorous, multi-site, National Institute on Aging-funded programme that tests potential anti-ageing drugs in genetically heterogeneous mice, has repeatedly confirmed rapamycin's lifespan-extending effects. The initial 2009 study by Harrison et al. in Nature showed that rapamycin extended median lifespan by 9% in males and 14% in females, even when started at 600 days of age (equivalent to roughly 60 human years). Subsequent ITP studies at higher doses showed even larger effects, with maximum lifespan extensions of up to 26% in females.

Rapamycin's effects extend beyond mere lifespan. Treated mice show reduced cancer incidence, improved cardiac function, enhanced immune responses to vaccination (paradoxically, given its use as an immunosuppressant), better cognitive function, and reduced age-related tissue degeneration. It is the closest thing to a broad-spectrum anti-ageing drug that has been demonstrated in mammals.

Human rapamycin trials

Translating rapamycin to human anti-ageing use faces significant challenges. At transplant doses (continuous, high-dose), rapamycin causes immunosuppression, impaired wound healing, insulin resistance, hyperlipidaemia, and mouth ulcers. The anti-ageing hypothesis is that low-dose, intermittent rapamycin might capture the longevity benefits without the side effects.

The PEARL (Participatory Evaluation of Aging with Rapamycin for Longevity) trial is testing low-dose rapamycin (5-10mg weekly) in healthy adults aged 50-85 for one year. Early safety data suggests the drug is well-tolerated at these doses, with side effects comparable to placebo. Results on biological ageing markers are expected by 2026-2027.

A separate trial by Novartis tested a rapamycin analogue called RTB101 (everolimus) in elderly adults. In a 2018 Science Translational Medicine paper, Mannick et al. showed that low-dose everolimus improved immune function in elderly adults, enhancing their response to the influenza vaccine by approximately 20%. However, a subsequent phase 3 trial of RTB101 for preventing respiratory tract infections in the elderly failed to meet its primary endpoint, leading Novartis to abandon the programme.

The rapamycin dilemma

The central question is whether you can get the autophagy-enhancing, anti-inflammatory, and anti-proliferative benefits of mTOR inhibition at doses low enough to avoid immunosuppression and metabolic side effects. Animal data suggests yes, but human data is insufficient to answer this definitively. A growing number of longevity-focused physicians prescribe low-dose rapamycin off-label (typically 3-6mg once weekly), but this practice is ahead of the evidence, and long-term safety in healthy adults is unknown.

NAD+ and sirtuins: separating hype from evidence

No molecule in the longevity space has generated more controversy than NAD+ (nicotinamide adenine dinucleotide). Championed primarily by David Sinclair of Harvard Medical School, the NAD+ hypothesis of ageing holds that declining NAD+ levels are a central driver of age-related decline, and that restoring NAD+ levels can reverse aspects of ageing. The theory has launched a multi-billion-pound supplement industry. The evidence, however, is considerably more complicated than the marketing suggests.

What NAD+ does

NAD+ is a coenzyme found in every living cell. It plays essential roles in cellular energy metabolism (serving as an electron carrier in glycolysis and the citric acid cycle), DNA repair (as a substrate for PARP enzymes), epigenetic regulation (as a substrate for sirtuins), and calcium signalling (as a precursor to cyclic ADP-ribose). NAD+ levels decline by approximately 50% between the ages of 40 and 60, as measured in multiple tissues. This decline is driven by increased consumption (more DNA damage means more PARP activity, which consumes NAD+) and decreased synthesis.

Sirtuins: the longevity genes?

Sirtuins are a family of seven NAD+-dependent deacetylase enzymes (SIRT1 through SIRT7) that regulate gene expression, DNA repair, mitochondrial function, and inflammation. In yeast, overexpression of Sir2 (the founding sirtuin) extended lifespan. In worms, extra copies of the sirtuin gene sir-2.1 extended lifespan by up to 50%. These early findings, published by Leonard Guarente and later David Sinclair, generated enormous excitement and the hypothesis that activating sirtuins could slow ageing in mammals.

The sirtuin story became more complicated when other labs attempted to replicate these results. A 2011 paper in Nature by Burnett et al. found that the lifespan extension attributed to sir-2.1 overexpression in worms was partly an artefact of genetic background, and the true effect was much smaller than originally reported (roughly 10 to 14% rather than 50%). In flies, the sirtuin lifespan extension similarly shrank upon closer examination. While SIRT1 overexpression in mice does improve metabolic health, it does not consistently extend maximum lifespan.

NMN and NR: the supplement frenzy

NMN (nicotinamide mononucleotide) and NR (nicotinamide riboside) are NAD+ precursors that can be taken orally to raise NAD+ blood levels. Both have been shown to increase NAD+ levels in human blood by 40 to 90% in multiple clinical trials. The question is whether raising NAD+ levels actually produces meaningful health benefits.

In mice, NMN supplementation has shown impressive results: improved insulin sensitivity, enhanced mitochondrial function, increased exercise capacity, better cardiovascular function, and in some studies, modest lifespan extension. These findings, largely from Sinclair's lab and others, drove consumer demand and turned NMN into a best-selling supplement despite limited human data.

Human trials have been less encouraging. The 2022 INTERSTELLAR trial, published in the New England Journal of Medicine, found that NMN supplementation for 60 days did not significantly improve biological age markers, insulin sensitivity, or physical performance in middle-aged and older adults compared to placebo. A 2023 trial of NR by Elysium Health (marketed as Basis) found that while NR raised NAD+ levels, it did not improve cardiovascular function, exercise capacity, or metabolic markers in healthy older adults.

The Brenner vs Sinclair debate

Charles Brenner, who first identified NR as an NAD+ precursor and holds key patents, has been a vocal critic of what he considers overhyped NAD+ claims. Brenner has argued that while NAD+ decline is real, the evidence that oral supplementation with NMN or NR produces clinically meaningful anti-ageing effects in humans is lacking. He has also criticised the quality of some studies from the Sinclair lab, pointing out methodological concerns and the conflation of animal findings with human expectations.

Sinclair maintains that NAD+ restoration is a genuine anti-ageing strategy and that negative human trials may have used inadequate doses or durations. He has also pointed to his own research showing that NMN can improve blood vessel function and endurance in aged mice, which he argues is biologically significant even if human translation takes time.

Metformin: the diabetes drug that might extend life

Metformin is one of the most prescribed drugs in the world, taken by over 150 million people with type 2 diabetes. It costs pennies per dose, has been used since the 1950s, and has a well-characterised safety profile. It is also one of the most intriguing candidates for a human anti-ageing drug, based on a peculiar observation: diabetics who take metformin appear to live as long as, or slightly longer than, non-diabetics who do not take it.

The Bannister 2014 study

The study that ignited interest in metformin as a longevity drug was published by Bannister et al. in 2014 in Diabetes, Obesity and Metabolism. Analysing UK Clinical Practice Research Datalink records covering 78,241 metformin-treated type 2 diabetes patients, 12,222 sulphonylurea-treated patients, and 90,463 matched non-diabetic controls, the researchers found something unexpected: metformin-treated diabetics had 15% lower all-cause mortality than matched non-diabetics. This was remarkable because type 2 diabetes is normally associated with reduced life expectancy. Sulphonylurea-treated diabetics, by contrast, had 38% higher mortality than controls.

This observational finding had obvious confounders. Metformin-treated patients were earlier in their disease course and healthier at baseline than sulphonylurea-treated patients. The non-diabetic controls may have included undiagnosed pre-diabetics with metabolic dysfunction. Selection bias was likely. Nonetheless, the finding was consistent with earlier observational studies suggesting that metformin use was associated with reduced cancer incidence, cardiovascular events, and all-cause mortality even after adjusting for diabetes severity.

How metformin might slow ageing

Metformin's primary mechanism is inhibition of mitochondrial complex I, which reduces cellular energy production and activates AMPK (AMP-activated protein kinase). AMPK activation mimics caloric restriction at the cellular level: it inhibits mTOR (promoting autophagy), reduces lipogenesis, improves insulin sensitivity, and reduces inflammation. Metformin also reduces advanced glycation end products (AGEs), which accumulate with age and contribute to vascular stiffness and tissue damage.

In the ITP mouse studies, metformin showed more modest lifespan effects than rapamycin. A 2013 study by Martin-Montalvo et al. in Nature Communications found that metformin extended mean lifespan by 5.83% in male mice at a dose of 0.1% in the diet. However, a higher dose (1%) actually shortened lifespan, suggesting a narrow therapeutic window. The ITP later tested metformin at multiple doses and found inconsistent results, with some studies showing no significant lifespan extension.

The TAME trial

The Targeting Aging with Metformin (TAME) trial, led by Nir Barzilai at the Albert Einstein College of Medicine, is the first clinical trial designed explicitly to test whether a drug can slow the ageing process in humans. The trial will enrol approximately 3,000 non-diabetic adults aged 65 to 79 and follow them for 4 to 6 years, measuring the time to onset of a composite endpoint of age-related diseases: cardiovascular events, cancer, dementia, and mortality. TAME began enrolling participants in 2024 after years of fundraising delays, and results are expected by 2027 to 2028.

Beyond the scientific question, TAME has a strategic regulatory goal. If the trial demonstrates that metformin delays multiple age-related diseases simultaneously, it could establish "ageing" as a treatable indication recognised by the FDA. This regulatory precedent would transform the entire field by creating a pathway for other anti-ageing drugs to be tested and approved.

Should you take metformin for longevity?

A growing number of longevity-focused physicians prescribe metformin off-label to non-diabetic patients. However, there is a significant concern: metformin may blunt the beneficial effects of exercise. A 2019 study by Konopka et al. found that metformin attenuated the improvements in skeletal muscle mitochondrial function and insulin sensitivity normally seen with exercise training. If you are already exercising regularly (which has far stronger anti-ageing evidence than metformin), adding metformin could partially negate those benefits. Until the TAME trial results are available, the risk-benefit calculus for healthy, active, non-diabetic individuals is genuinely uncertain.

GLP-1 agonists: beyond weight loss

Semaglutide (Ozempic, Wegovy) and tirzepatide (Mounjaro) have become the most talked-about drugs in medicine over the past three years, primarily for their dramatic weight loss effects. But accumulating evidence suggests these GLP-1 receptor agonists may have longevity benefits that extend well beyond adiposity reduction.

Cardiovascular protection: the SELECT trial

The SELECT trial (Semaglutide Effects on Cardiovascular Outcomes in People with Overweight or Obesity), published in 2023 in the New England Journal of Medicine, enrolled 17,604 adults with overweight or obesity and established cardiovascular disease, but without diabetes. Participants receiving semaglutide 2.4mg weekly had a 20% reduction in major adverse cardiovascular events (cardiovascular death, non-fatal myocardial infarction, or non-fatal stroke) compared to placebo over a median 33-month follow-up. All-cause mortality showed a non-significant trend towards reduction (approximately 15%).

This was groundbreaking because the cardiovascular benefits appeared to exceed what would be expected from weight loss alone. Mechanistically, GLP-1 agonists reduce arterial inflammation, improve endothelial function, reduce oxidative stress, and directly protect cardiomyocytes from ischaemic injury. These are hallmark-level effects: addressing inflammation, mitochondrial function, and cellular stress responses.

Kidney protection

The FLOW trial, also published in 2024, demonstrated that semaglutide reduced the risk of kidney disease progression by 24% in patients with type 2 diabetes and chronic kidney disease. Since kidney function decline is one of the most consistent features of biological ageing, this finding has implications beyond nephrology.

Emerging longevity signals

Observational data and secondary analyses are beginning to hint at broader anti-ageing effects. GLP-1 agonist use has been associated with reduced incidence of Alzheimer's disease in retrospective cohort studies, improved liver function (reduced NAFLD progression), reduced risk of certain cancers, and lower all-cause mortality. However, these are observational findings subject to confounding, and prospective trials specifically designed to test longevity endpoints have not yet been completed.

Some longevity researchers speculate that GLP-1 agonists may function as partial caloric restriction mimetics, reducing food intake and body weight while activating cellular stress response pathways similar to those engaged by fasting. If this hypothesis is correct, they could represent a more tolerable alternative to the severe caloric restriction that has been shown to extend lifespan in nearly every organism tested.

Stem cells and young blood: the evidence vs the hype

Few areas of anti-ageing science have generated as much controversy as stem cell therapy and young blood transfusion. The scientific foundations are genuine, but the clinical landscape has been polluted by unregulated clinics offering unproven (and sometimes dangerous) treatments to desperate patients.

The parabiosis experiments

The modern era of young blood research began with heterochronic parabiosis experiments by Irina and Michael Conboy at UC Berkeley. In these experiments, the circulatory systems of old and young mice were surgically joined, so that they shared the same blood supply. The results, published in Nature in 2005, showed that exposure to young blood rejuvenated aged muscle stem cells, improved liver regeneration, and enhanced neurogenesis in old mice. Conversely, exposure to old blood impaired regeneration in young mice.

These findings sparked a wave of enthusiasm and a search for the "youth factors" in young blood. GDF11 was initially identified as a candidate rejuvenation factor by Amy Wagers's lab at Harvard, but subsequent studies by the Conboy lab and others failed to replicate the anti-ageing effects of GDF11, and some found that high GDF11 levels were actually associated with frailty and disease. The Conboys themselves have argued that the rejuvenating effects of parabiosis may be less about young blood containing magical factors and more about diluting harmful factors that accumulate in old blood (such as elevated TGF-beta, CCL11, and B2-microglobulin).

Young blood transfusion: the Ambrosia debacle

In 2016, a startup called Ambrosia began offering young blood plasma transfusions to paying customers at $8,000 per litre. The company ran a "clinical trial" with no control group that purported to show benefits from young plasma. In 2019, the FDA issued a warning statement cautioning consumers against young blood transfusions, noting that there was no proven clinical benefit and that plasma transfusion carries real risks (allergic reactions, transfusion-related acute lung injury, and infectious disease transmission). Ambrosia subsequently shut down, though it briefly attempted to reopen.

Where stem cell science actually stands

Legitimate stem cell research continues in regulated clinical trials. Mesenchymal stem cell (MSC) infusions are being tested for age-related frailty, with a 2017 phase 1/2 trial by Tompkins et al. in the Journals of Gerontology showing that allogeneic MSC infusions improved physical performance and reduced inflammatory biomarkers in elderly frail patients. However, the optimal cell source, dose, frequency, and patient selection remain unresolved, and no stem cell therapy has been approved by the FDA for anti-ageing indications.

The most promising near-term application may be in specific age-related diseases rather than general anti-ageing. Stem cell therapies for age-related macular degeneration, osteoarthritis, and heart failure are in phase 2 and 3 trials with varying results. The broader aspiration of using stem cells to comprehensively rejuvenate the ageing body remains years, if not decades, from clinical reality.

CRISPR and gene therapy: the distant frontier

Gene editing technologies, particularly CRISPR-Cas9, have revolutionised biological research and are beginning to enter clinical medicine. But their application to human ageing is almost entirely theoretical at this point, and the ethical, safety, and practical barriers are formidable.

What has been done in animals

Researchers have used CRISPR to target specific ageing pathways in mice with provocative results. In 2019, a team from the Salk Institute used CRISPR-based gene activation to partially reprogram cells in progeria mice (which have accelerated ageing due to mutations in the lamin A gene), extending their lifespan by 30%. A 2022 study used CRISPR to knock out specific genes involved in senescent cell survival, reducing senescent cell burden and improving healthspan markers in aged mice.

Gene therapy approaches (delivering functional copies of genes rather than editing existing genes) have also shown potential. Delivery of telomerase (TERT) via adeno-associated virus (AAV) extended lifespan in mice by 13 to 24% without increasing cancer rates (Bernardes de Jesus et al., 2012, EMBO Molecular Medicine). Delivery of three longevity-associated genes (TERT, follistatin, and a soluble form of the TGF-beta receptor) simultaneously extended lifespan and improved healthspan markers in aged mice (Davidsohn et al., 2019).

The barriers to human application

Translating these findings to humans faces fundamental challenges:

• Delivery: Delivering gene therapies to enough cells in the right tissues of an adult human body is enormously difficult. AAV vectors have limited cargo capacity, trigger immune responses with repeated dosing, and preferentially transduce the liver rather than other target tissues.
• Safety: Off-target editing (CRISPR cutting at unintended sites) could introduce cancer-causing mutations. While off-target rates have improved dramatically, the consequences of even rare errors in billions of cells are significant.
• Complexity: Ageing involves hundreds or thousands of genes across every tissue. Editing a handful of genes is unlikely to comprehensively reverse ageing the way it can in simple genetic diseases.
• Regulation: Germline editing (changes that pass to future generations) is effectively banned in most countries. Somatic gene therapy for ageing would need to demonstrate safety over decades, not months.
• Ethics: If gene therapies for ageing become available, issues of access, equity, and the societal implications of dramatically extended lifespans become pressing. These are not reasons to halt research, but they are reasons to proceed thoughtfully.

Biological age testing: what you can measure today

The concept of biological age, how old your body actually is versus how old the calendar says you are, has moved from academic curiosity to consumer product. Multiple commercial tests now claim to measure your biological age. Here is what they actually test, and how reliable they are.

Epigenetic age tests

Companies like TruAge (TruDiagnostic), GlycanAge, Elysium (Index), and myDNAge offer methylation-based biological age testing. These tests typically require a blood sample and use one or more epigenetic clocks (Horvath, GrimAge, DunedinPACE, or proprietary algorithms) to estimate biological age. Prices range from $200 to $500 per test. The technology is real, but interpretation requires caution: biological age estimates can vary by several years between tests taken on the same day, and the clinical significance of being "3 years younger" biologically is not yet clear in terms of actionable guidance.

Telomere length testing

Telomere length can be measured through quantitative PCR (qPCR), flow-FISH, or terminal restriction fragment (TRF) analysis. Consumer tests typically use qPCR, which is the least precise method. Telomere length measurements are highly variable between labs and even between blood draws, and as discussed above, telomere length is a modest predictor of individual outcomes. Consumer telomere testing is available from companies like Life Length and SpectraCell for approximately $200 to $400.

Blood biomarker panels

Multiple blood biomarkers change predictably with age and can be assembled into biological age estimates. These include high-sensitivity C-reactive protein (hsCRP, a measure of inflammation), glycated haemoglobin (HbA1c, a measure of blood sugar control), cystatin C (kidney function), GDF-15 (a stress-response protein), and albumin (liver synthetic function). Companies like InsideTracker and Levine's PhenoAge algorithm use panels of such biomarkers to estimate biological age. These tests have the advantage of being based on clinically validated blood markers with clear health implications.

The supplement graveyard

The anti-ageing supplement market is projected to exceed $100 billion globally by 2027. Most of this spending is on products with weak, conflicting, or non-existent human evidence. Here is an honest accounting of the most popular anti-ageing supplements.

Resveratrol: the fallen star

Resveratrol, the polyphenol found in red wine and grape skins, was the original sirtuin-activating compound (STAC). Sinclair's 2006 Nature paper showing that resveratrol extended lifespan in obese mice by 31% generated enormous media coverage. GlaxoSmithKline purchased Sirtris Pharmaceuticals (Sinclair's resveratrol company) for $720 million in 2008. But the story unravelled. Resveratrol did not extend lifespan in normal-weight mice (only in obese mice, likely because it improved their metabolic dysfunction). Its oral bioavailability is extremely poor (less than 1% reaches the bloodstream intact). GlaxoSmithKline shut down the Sirtris programme in 2013. Human trials of resveratrol for cardiovascular disease, cancer, and cognitive decline have been overwhelmingly negative. Resveratrol supplements are, by 2026, one of the clearest examples of a supplement that was aggressively marketed based on animal data that did not translate to humans.

CoQ10 (Coenzyme Q10)

CoQ10 is a component of the mitochondrial electron transport chain and a lipid-soluble antioxidant. Levels decline with age, particularly in the heart and brain. Supplementation is popular among people taking statins (which reduce CoQ10 synthesis) and those seeking anti-ageing benefits. The evidence for anti-ageing effects is weak. A 2014 trial (Q-SYMBIO) showed CoQ10 reduced cardiovascular events in heart failure patients, but this was in a disease population, not healthy agers. No study has shown that CoQ10 supplementation extends lifespan or slows biological ageing in humans. It is reasonably safe but likely does little for people without heart failure or statin-related side effects.

NMN (Nicotinamide mononucleotide)

Covered in detail in the NAD+ section above. The short version: raises NAD+ levels effectively, but no human trial has shown it slows biological ageing. The FDA's 2022 decision to classify NMN as an investigational drug (potentially removing it from the supplement market) added regulatory uncertainty. Multiple companies continue to sell NMN as a supplement, often at prices exceeding $50 to $100 per month.

Alpha-ketoglutarate (AKG)

AKG is a metabolite of the citric acid cycle involved in amino acid synthesis, epigenetic regulation, and collagen production. A 2020 study in Cell Metabolism by Asadi Shahmirzadi et al. reported that alpha-ketoglutarate extended lifespan by 12% in female mice and reduced frailty. A calcium-AKG formulation (Rejuvant) showed a 7-year reduction in biological age (TruAge clock) in a small, non-placebo-controlled human study. However, the study was company-sponsored, small (n=42), lacked a proper control group, and has not been replicated. AKG supplementation is relatively inexpensive and likely safe, but the evidence base remains thin.

Spermidine

Spermidine, a polyamine found in wheat germ, aged cheese, and mushrooms, is one of the more promising supplement candidates. It induces autophagy independently of mTOR and has extended lifespan in yeast, worms, flies, and mice. Epidemiological data from the Bruneck Study (Kiechl et al., 2018, American Journal of Clinical Nutrition) showed that higher dietary spermidine intake was associated with reduced all-cause mortality in an 800-person cohort followed for 20 years. A small randomised trial showed improved cognitive function in older adults with subjective cognitive decline. However, no large-scale RCT has tested spermidine for lifespan extension in humans.

Vitamin D

Vitamin D deficiency is common, particularly in northern latitudes, and is associated with increased all-cause mortality, cardiovascular disease, cancer, and immune dysfunction. However, the large VITAL trial (25,871 participants) found that vitamin D supplementation in non-deficient adults did not reduce the incidence of cancer or cardiovascular events. The consensus is that correcting deficiency is beneficial, but supplementing beyond sufficiency provides minimal additional benefit. If your blood level is below 30 ng/ml (75 nmol/L), supplementation is clearly warranted.

Omega-3 fatty acids

Omega-3 fatty acids (EPA and DHA) have the strongest human evidence base among conventional supplements, though even this evidence is complicated. The REDUCE-IT trial showed that high-dose EPA (icosapent ethyl, 4g/day) reduced cardiovascular events by 25% in statin-treated patients with elevated triglycerides. However, the STRENGTH trial of a different omega-3 formulation showed no benefit. A 2021 meta-analysis in the BMJ covering 38 trials and 149,000 participants found modest cardiovascular benefits from omega-3 supplementation but no clear effect on all-cause mortality.

Caloric restriction vs time-restricted eating vs pharmaceutical mimetics

Caloric restriction (CR) is the oldest and most consistently validated anti-ageing intervention in biology. Restricting caloric intake by 20 to 40% without malnutrition extends lifespan in yeast, worms, flies, mice, rats, and possibly primates. The question is whether this translates to humans, and whether the same benefits can be achieved through less extreme approaches like time-restricted eating or drugs that mimic CR's cellular effects.

Caloric restriction in primates

Two major CR studies in rhesus monkeys produced seemingly contradictory results that were eventually reconciled. The Wisconsin National Primate Research Center study (Colman et al., 2009 and 2014) showed that 30% CR begun in adulthood reduced age-related mortality by 3-fold and delayed the onset of diabetes, cardiovascular disease, cancer, and brain atrophy. The NIA study (Mattison et al., 2012 and 2017) initially appeared negative but ultimately showed that CR improved health metrics (particularly metabolic health and body composition) even though the lifespan extension was smaller. The key difference was that the NIA control group was already somewhat calorie-restricted compared to ad libitum-fed controls, narrowing the gap between groups.

The CALERIE trial: CR in humans

The Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy (CALERIE) trial is the only completed randomised controlled trial of sustained CR in non-obese humans. Published by Ravussin et al. in 2015 in JAMA Internal Medicine, CALERIE randomised 218 healthy, non-obese adults (BMI 22-28) to either 25% caloric restriction or ad libitum eating for 2 years. The CR group achieved approximately 12% sustained caloric restriction (less than the target, reflecting the difficulty of maintaining severe CR).

Even this modest restriction produced measurable benefits: reduced thyroid hormone levels (associated with longevity in animal models), lower C-reactive protein, reduced oxidative stress, improved insulin sensitivity, decreased metabolic rate, and weight loss averaging 7.5 kg. A 2023 secondary analysis of CALERIE data showed that CR significantly slowed the DunedinPACE measure of biological ageing by 2 to 3%, suggesting that even modest sustained caloric restriction measurably decelerates the ageing process.

Time-restricted eating (intermittent fasting)

Time-restricted eating (TRE), where food intake is limited to a window of 8 to 12 hours per day, has gained enormous popularity as a more sustainable alternative to continuous CR. The scientific rationale is that TRE aligns eating with circadian rhythms and may provide metabolic benefits through daily fasting periods, independent of total caloric intake.

The evidence is mixed. Short-term studies (8 to 12 weeks) consistently show improvements in body weight, insulin sensitivity, and inflammatory markers. However, longer studies have been less impressive. A 2022 study in the New England Journal of Medicine by Liu et al. found that time-restricted eating (eating only between 8am and 4pm) produced no additional weight loss or metabolic benefit compared to simple caloric restriction over 12 months when total caloric intake was matched. This suggests that the benefits of TRE may be primarily due to reduced total caloric intake rather than the timing of eating per se.

A concerning 2024 analysis from the American Heart Association presented data suggesting that an eating window of less than 8 hours per day was associated with a 91% higher risk of cardiovascular death. However, this was an observational study with significant methodological limitations, including self-reported dietary data from only two days and potential confounders (people eating in very narrow windows may have had underlying health conditions or disordered eating).

Pharmaceutical CR mimetics

Given that sustained caloric restriction is difficult for most humans, there is intense interest in drugs that mimic CR's cellular effects. The leading candidates are rapamycin (mTOR inhibition), metformin (AMPK activation), and potentially GLP-1 agonists (appetite suppression and metabolic improvement). As discussed in previous sections, each has varying levels of evidence. The ideal CR mimetic would activate autophagy, improve insulin sensitivity, reduce inflammation, and enhance mitochondrial function without requiring people to be perpetually hungry. We are not there yet, but the pharmacological pipeline is active.

The longevity industry: who is funding the race

The longevity industry has exploded from a fringe scientific backwater into a multi-billion-pound sector attracting some of the wealthiest people on the planet. Understanding who is funding this research, and what their motivations are, matters because it shapes which approaches get tested and which get ignored.

Altos Labs

Founded in 2022 with an initial investment reportedly exceeding $3 billion, Altos Labs is the most lavishly funded longevity company in history. Backed by Jeff Bezos and the late Yuri Milner, Altos focuses on cellular reprogramming, the idea that exposing aged cells to Yamanaka factors (Oct4, Sox2, Klf4, and c-Myc) can reset their epigenetic age while maintaining their differentiated identity. This approach, demonstrated in mice by Ocampo et al. in 2016 and expanded by multiple groups since, effectively reverses the epigenetic clock of treated cells. The challenge is controlling the process: too much reprogramming turns cells into induced pluripotent stem cells (iPSCs) or causes teratomas (tumours). Altos has hired some of the most distinguished scientists in the field, including Shinya Yamanaka (Nobel laureate for discovering iPSCs), Steve Horvath (inventor of the epigenetic clock), and Juan Carlos Izpisua Belmonte (pioneer of in vivo reprogramming).

Calico (California Life Company)

Founded by Google in 2013 with an initial investment of $1.5 billion (supplemented by a partnership with AbbVie worth another $1.5 billion), Calico operates with extraordinary secrecy. The company is led by Arthur Levinson (former CEO of Genentech) and has published relatively little given its enormous funding. What has emerged suggests a focus on basic ageing biology, particularly in the naked mole-rat (a species that shows negligible senescence and rarely develops cancer despite living 30+ years). Critics argue that Calico has underperformed relative to its funding, producing more publications than products.

Unity Biotechnology

Founded in 2011 to develop senolytic drugs, Unity was backed by Jeff Bezos, Peter Thiel, and other tech luminaries. After the phase 2 failure of UBX0101 for osteoarthritis in 2020, the company pivoted to ophthalmology and has shown more promising results with foselutoclax for age-related eye diseases. Unity's trajectory illustrates a common pattern in longevity biotech: dramatic animal data, followed by humbling human results, followed by strategic repositioning.

Other notable players

• Loyal (for dogs): A company developing longevity drugs specifically for dogs, which serve as a faster testing ground for anti-ageing interventions. In 2024, Loyal received conditional FDA approval for LOY-001, a drug targeting IGF-1 in large-breed dogs. If a dog longevity drug works, the path to human testing may accelerate.
• Retro Biosciences: Backed by Sam Altman (CEO of OpenAI) with a $180 million investment, Retro focuses on cellular reprogramming, autophagy, and plasma-inspired therapeutics.
• NewLimit: Co-founded by Brian Armstrong (CEO of Coinbase), NewLimit is working on epigenetic reprogramming to restore youthful gene expression patterns.
• Hevolution Foundation: A Saudi Arabia-backed non-profit with a $1 billion annual budget dedicated to funding ageing research globally. Hevolution has funded the TAME trial and numerous academic geroscience programmes.

The influx of money has been a double-edged sword. On one hand, it has accelerated research and attracted top scientific talent. On the other hand, it has created hype cycles, inflated expectations, and in some cases funded approaches that are more marketable than scientifically rigorous. The gap between what longevity companies claim in their pitch decks and what the published evidence supports remains wide.

How Death Clock factors in biological ageing

Death Clock integrates multiple dimensions of ageing science into its lifespan estimation model. Rather than relying on a single biomarker or clock, our approach reflects the reality that ageing is multifactorial and that your remaining lifespan is determined by the interplay of dozens of variables.

What we measure and why

Death Clock incorporates 38 modifiable and non-modifiable factors that influence lifespan. Many of these map directly onto the hallmarks of ageing discussed throughout this article:

• Lifestyle factors (exercise, diet, sleep, smoking, alcohol) that affect telomere attrition, epigenetic ageing, inflammation, and mitochondrial function.
• Metabolic markers (BMI, diabetes status, blood pressure) that reflect deregulated nutrient sensing and metabolic dysfunction.
• Chronic disease status that indicates accumulated cellular damage and systemic dysfunction.
• Psychological and social factors (stress, social connection, mental health) that influence epigenetic ageing and inflammation through neuroendocrine pathways.
• Environmental exposures (air quality, occupational hazards) that contribute to genomic instability and mitochondrial damage.

Our model weights these factors based on the strength of their epidemiological evidence, drawing from the same large-scale studies and meta-analyses referenced throughout this article. The result is a personalised estimate that reflects your unique combination of risk factors and protective behaviours.

Beyond a single number

The most valuable output from Death Clock is not the estimated date of death (which is inherently uncertain for any individual) but the identification of which factors are having the largest impact on your projected lifespan. If your model shows that sedentary behaviour is costing you 4 years and smoking is costing you 10 years, you have actionable information. You know exactly which hallmarks of ageing are being most aggressively accelerated in your body, and you know which interventions are most likely to slow them.

This is the bridge between ageing science and practical behaviour change. The hallmarks of ageing are fascinating biology, but they are also a road map for personal action. Every factor in the Death Clock model connects to one or more hallmarks, and every improvement you make addresses at least one mechanism of biological ageing.

Study reference table

The following table summarises key studies referenced throughout this article, organised by topic. All studies are peer-reviewed publications in major journals.

What does this mean for your death clock?

The science of ageing has never been more advanced, and it has never been more cluttered with hype. Here is what actually matters for your personal longevity, based on the totality of evidence reviewed in this article:

1. Exercise is the best anti-ageing drug. It addresses more hallmarks of ageing than any pharmaceutical intervention currently available. Aim for 150 minutes of moderate aerobic activity plus 2 sessions of resistance training per week.
2. Do not smoke. Smoking accelerates every hallmark of ageing and remains the single largest modifiable risk factor for premature death.
3. Maintain a healthy weight. Obesity accelerates epigenetic ageing, promotes senescent cell accumulation, increases inflammation, and disrupts metabolic signalling.
4. Sleep 7 hours per night. Sleep is when your brain clears waste proteins, your immune system rebuilds, and your tissues repair themselves.
5. Eat a Mediterranean-style diet. High in vegetables, fruits, whole grains, legumes, fish, and olive oil. Associated with longer telomeres, slower epigenetic ageing, and reduced all-cause mortality across dozens of studies.
6. Manage chronic stress. Psychological stress accelerates telomere shortening and epigenetic ageing. Meditation, social connection, therapy, and time in nature all have evidence for stress reduction.
7. Get your biomarkers checked. Blood pressure, HbA1c, lipids, vitamin D, and inflammatory markers give you actionable data about your metabolic health and biological age.
8. Be sceptical of supplements. Most anti-ageing supplements have stronger marketing than evidence. Focus your spending on whole food, gym memberships, and medical check-ups instead.
9. Watch the pharmaceutical pipeline. Rapamycin, senolytics, and GLP-1 agonists are the most promising pharmacological anti-ageing interventions. Within 10 years, we may have approved drugs that genuinely slow ageing. Until then, the lifestyle fundamentals remain your best investment.

The race to slow ageing is real. Billions of pounds are funding serious science. But the finish line is further away than the headlines suggest, and the best tools available today are the ones your grandparents would have recognised: move your body, eat well, sleep enough, do not smoke, and stay connected to people you love. Your death clock is not fixed. The hallmarks of ageing are targetable. Start with what the evidence actually supports.