Longevity Glossary

Stable adducts formed by the non-enzymatic reaction of glucose (or other reducing sugars) with proteins, lipids, or nucleic acids — a process called glycation. AGEs accumulate with age and with chronic hyperglycemia, cross-linking structural proteins (like collagen) and activating inflammatory receptors (RAGE). They are implicated in diabetic complications, cardiovascular stiffening, cataracts, and accelerated tissue aging.

AMP-activated protein kinase — a master energy sensor that is activated when cellular ATP is low (high AMP:ATP ratio). AMPK activation promotes catabolic processes (glucose uptake, fatty acid oxidation, autophagy) and inhibits anabolic processes (lipid and protein synthesis). It is considered a major longevity-promoting kinase and is activated by exercise, caloric restriction, metformin, and berberine.

A therapeutic or lifestyle strategy aimed at increasing the activity of AMPK, the cellular energy sensor. Methods include exercise (particularly zone 2 and HIIT), caloric restriction, cold exposure, metformin, berberine, and AICAR. AMPK activation promotes autophagy, mitochondrial biogenesis, glucose uptake, and fatty acid oxidation while inhibiting mTORC1 — producing a profile of beneficial metabolic adaptations relevant to longevity.

Apolipoprotein B — a structural protein present on every atherogenic lipoprotein particle (LDL, VLDL, IDL, Lp(a)). Each particle carries exactly one ApoB molecule, so ApoB directly counts the number of atherogenic particles in blood — making it a superior predictor of cardiovascular risk compared to LDL-C alone. Leading longevity physicians consider ApoB the primary lipid target for cardiovascular risk reduction.

Apolipoprotein E — a lipid transport protein encoded by the APOE gene with three common allelic variants: ε2, ε3, and ε4. APOEε4 is the strongest genetic risk factor for late-onset Alzheimer's disease: one copy roughly triples risk, two copies increase risk approximately 12-fold. APOEε2 is associated with reduced cardiovascular and Alzheimer's risk and mild longevity benefit. APOEε3 is the neutral common allele.

Programmed cell death — a highly regulated process by which cells dismantle themselves in an orderly fashion. Unlike necrosis, apoptosis does not trigger inflammation and is essential for development, immune function, and tissue homeostasis. Dysregulation of apoptosis contributes to cancer (too little) and neurodegeneration (too much).

A cellular 'self-eating' recycling process in which damaged proteins and organelles are sequestered in autophagosomes and degraded by lysosomes. Autophagy is a major quality-control mechanism and is strongly induced by fasting, caloric restriction, and mTOR inhibition. Impaired autophagy is linked to neurodegeneration, cancer, and accelerated aging.

The dynamic rate at which the autophagy pathway operates end-to-end, from autophagosome formation through lysosomal degradation and recycling. High flux indicates active and efficient cellular recycling, while impaired flux — even with high autophagosome numbers — can indicate a bottleneck in lysosomal clearance. Flux measurement requires specific assays using lysosomal inhibitors.

An estimate of how old a person's body is physiologically, as distinct from chronological age. Biological age can be measured using epigenetic clocks (DNA methylation patterns), composite biomarker panels, telomere length, or functional metrics like VO2 max and grip strength. A biological age lower than chronological age indicates slower aging; higher indicates accelerated aging.

A dietary regimen that reduces total caloric intake by 20–40% below ad libitum levels without malnutrition. Caloric restriction is the most consistently effective intervention to extend healthy lifespan across a wide range of organisms, from yeast and worms to rodents and non-human primates. It acts through AMPK activation, mTOR inhibition, enhanced autophagy, reduced IGF-1 signaling, and improved metabolic efficiency.

The process of reverting a differentiated somatic cell toward a more youthful or pluripotent state, typically by transiently expressing Yamanaka factors (Oct4, Sox2, Klf4, c-Myc). Partial reprogramming has been shown to rejuvenate epigenetic age and restore function in aged cells without losing cell identity. This approach is a leading frontier in rejuvenation biotechnology.

The primary glucocorticoid stress hormone produced by the adrenal cortex. Cortisol mobilizes energy, suppresses inflammation acutely, and modulates immune function — all adaptive in the short term. Chronically elevated cortisol, as in psychological stress or Cushing syndrome, accelerates cellular aging, impairs memory, increases visceral fat, and suppresses immune function and testosterone production.

A tyrosine kinase inhibitor (BCR-ABL, Src family) originally developed as a cancer chemotherapy. Dasatinib was repurposed as a senolytic after being identified in a computational screen targeting senescent cell survival pathways. It is most commonly used in combination with quercetin (D+Q), the most clinically advanced senolytic combination, which is in phase 2 trials for frailty, IPF, diabetic kidney disease, and Alzheimer's disease.

Dehydroepiandrosterone — an adrenal steroid and the most abundant circulating steroid in humans, serving as a precursor for both androgens and estrogens. DHEA levels peak in the mid-20s and decline by roughly 80–90% by age 70–80, one of the most dramatic hormone changes of aging. Low DHEA-S (its sulfated form) is associated with cardiovascular disease, insulin resistance, and reduced quality of life.

A DNA methylation-based algorithm that measures the pace of aging — how fast a person is aging per calendar year — rather than a static biological age estimate. Developed from the Dunedin birth cohort study, DunedinPACE (Pace of Aging Computed from the Epigenome) correlates with cognitive and physical decline and is more sensitive to lifestyle and pharmacological intervention effects than static clocks.

Estimated glomerular filtration rate — a calculated measure of kidney filtration function based on serum creatinine, age, and sex. eGFR (mL/min/1.73m²) is the primary staging criterion for chronic kidney disease (CKD). Age-related decline in eGFR is expected (approximately 1 mL/min/year after 40), but accelerated decline indicates active kidney disease. Optimal eGFR for longevity is above 90.

A computational model that estimates biological age from patterns of DNA methylation at specific CpG sites across the genome. Epigenetic clocks (Horvath, Hannum, GrimAge, DunedinPACE, and others) are the most accurate current measures of biological age and are sensitive to lifestyle, environmental exposures, and pharmacological interventions. They predict mortality, disease risk, and functional decline better than chronological age.

The study of heritable changes in gene expression that do not involve alterations to the DNA sequence itself. Epigenetic modifications — including DNA methylation, histone acetylation, and chromatin remodeling — regulate which genes are active in a given cell. Epigenetic changes accumulate with age and are a primary readout of biological age.

The complete set of epigenetic modifications present in a cell — including DNA methylation, histone modifications, chromatin accessibility, and non-coding RNA profiles. Unlike the genome (DNA sequence), the epigenome is dynamic and can be altered by lifestyle, environment, and aging. Epigenomic reprogramming is central to both the aging process and emerging rejuvenation strategies.

A flavonoid polyphenol found in strawberries, apples, and other fruits that demonstrates senolytic and antioxidant activity. Fisetin cleared approximately 25–50% of senescent cells in aged mouse tissues in Mayo Clinic studies and modestly extended mouse lifespan. It is better tolerated than dasatinib but its senolytic efficacy in humans remains under investigation in ongoing clinical trials (NCT04210986).

A transcription factor belonging to the forkhead box O family that is a critical regulator of longevity pathways. FOXO3 activates genes involved in stress resistance, DNA repair, apoptosis, and autophagy. It is one of the most replicated longevity-associated genes in humans: variants near FOXO3 are consistently enriched in centenarians across multiple ethnic groups.

Growth differentiation factor 11 — a TGF-β superfamily member initially identified as a potential circulating rejuvenation factor based on heterochronic parabiosis studies. GDF11 levels were reported to decline with age and reverse cardiac hypertrophy in old mice when supplemented. Subsequent research has been controversial, with some studies failing to replicate initial findings; its role in aging remains actively debated.

The spontaneous, non-enzymatic attachment of a sugar molecule (most commonly glucose) to a protein or lipid. Unlike enzymatic glycosylation, glycation is random and typically damaging, impairing protein function and generating reactive carbonyl species. HbA1c is a clinical measure of glycation. Reducing dietary sugar and glycemic load is the primary strategy to minimize pathological glycation.

A second-generation epigenetic clock developed by Steve Horvath and colleagues that predicts time-to-death and onset of age-related disease with high accuracy. GrimAge is trained on smoking pack-years and plasma proteins associated with mortality (including GDF15, PAI-1, and others), making it more clinically actionable than first-generation clocks. GrimAge acceleration (GrimAge > chronological age) is a strong predictor of morbidity.

A peptide hormone secreted by the anterior pituitary that stimulates IGF-1 production, promotes muscle anabolism, lipolysis, and bone growth. GH secretion declines with age (somatopause), contributing to increased fat mass, reduced muscle mass, and decreased bone density. While GH replacement is used clinically in deficiency states, supraphysiologic use carries risks including increased cancer risk and insulin resistance.

Hemoglobin A1c (glycated hemoglobin) — a measure of the percentage of hemoglobin molecules that have been glycated by glucose. It reflects average blood glucose over the preceding 2–3 months and is the gold standard for monitoring long-term glycemic control. Optimal longevity-focused HbA1c is typically below 5.3%; values above 5.7% indicate prediabetes.

An experimental technique in which the circulatory systems of a young and old animal are surgically joined so they share blood. Studies in rodents have shown that young blood can rejuvenate aged tissues, while old blood accelerates aging in young animals, implicating circulating factors — including GDF11, oxytocin, and growth differentiation factors — as key mediators of systemic aging.

Homeostatic Model Assessment of Insulin Resistance — a calculated index using fasting glucose and fasting insulin to estimate insulin resistance. HOMA-IR = (fasting glucose [mg/dL] × fasting insulin [µIU/mL]) / 405. Values above 1.5–2.0 suggest insulin resistance. It is a widely used clinical and research tool, though it underestimates resistance in severe cases.

A biological phenomenon in which exposure to a mild stressor produces an adaptive beneficial response, often described as a biphasic dose-response: low doses are beneficial while high doses are harmful. In the context of aging, hormetic stressors include exercise, fasting, heat stress (sauna), cold exposure, and low-dose xenobiotics. These stressors activate stress response pathways (AMPK, FOXO3, Nrf2) that improve cellular resilience.

The original multi-tissue epigenetic clock developed by Steve Horvath in 2013, using 353 CpG methylation sites to estimate biological age across virtually all human tissues. The Horvath clock was a landmark discovery demonstrating that aging leaves a precise molecular signature in DNA methylation. Its 'age acceleration' metric — the gap between epigenetic and chronological age — predicts all-cause mortality independently of other risk factors.

High-sensitivity C-reactive protein — an acute-phase reactant produced by the liver in response to systemic inflammation, measured at the high-sensitivity level (0.1 mg/L resolution). hsCRP is used as a cardiovascular risk marker; levels above 3 mg/L indicate high cardiovascular risk. Chronically elevated hsCRP is also associated with accelerated aging, cancer risk, and cognitive decline. Optimal level for longevity is below 0.5 mg/L.

Insulin-like growth factor 1 — a peptide hormone structurally similar to insulin, primarily secreted by the liver in response to growth hormone. IGF-1 promotes cell growth, proliferation, and survival. While it is anabolic and important for muscle and bone maintenance, chronically elevated IGF-1 is associated with accelerated aging in model organisms; reduced IGF-1 signaling extends lifespan in worms, flies, and mice.

An anabolic peptide hormone produced by pancreatic beta cells that regulates glucose uptake, glycogen synthesis, protein synthesis, and fat storage. Chronically elevated insulin levels (hyperinsulinemia), often preceding type 2 diabetes by years, drive insulin resistance, promote inflammation, activate mTOR, and suppress autophagy — all accelerating aging pathways.

A condition in which cells fail to respond normally to insulin, requiring progressively higher insulin secretion to maintain normal blood glucose. Insulin resistance precedes type 2 diabetes by years and is a root cause of metabolic syndrome, NAFLD, PCOS, cardiovascular disease, and accelerated aging. It promotes chronic mTOR activation, inflammation, and reduced AMPK/sirtuin activity.

A metabolic state in which the liver produces ketone bodies (beta-hydroxybutyrate, acetoacetate, acetone) from fatty acid oxidation as an alternative fuel when carbohydrate availability is low, such as during fasting, prolonged exercise, or a ketogenic diet. Ketones serve as an efficient fuel for the brain and heart and may have direct signaling roles that promote autophagy, HDAC inhibition, and anti-inflammatory effects.

A pleiotropic protein that functions both as a membrane co-receptor for FGF23 and as a secreted hormone. Klotho deficiency in mice causes a premature aging syndrome resembling human aging, while overexpression extends lifespan. Circulating Klotho declines with age and is associated with kidney function, cognitive performance, and cardiovascular health.

Lipoprotein(a) — a variant LDL particle in which apolipoprotein(a) is covalently attached to ApoB. Lp(a) levels are largely genetically determined and do not respond significantly to lifestyle changes. High Lp(a) — above approximately 50 mg/dL or 125 nmol/L — is an independent risk factor for atherosclerotic cardiovascular disease, aortic stenosis, and stroke. Novel RNA-targeting therapies (antisense oligonucleotides, siRNA) are under clinical development.

A hormone produced by the pineal gland primarily at night that regulates circadian rhythm and sleep-wake cycles. Beyond its role in sleep, melatonin is a potent antioxidant and has anti-inflammatory properties. Melatonin production declines with age, contributing to sleep disturbances common in older adults. It is among the most widely used supplements globally.

A cluster of metabolic abnormalities — typically including abdominal obesity, elevated triglycerides, low HDL cholesterol, hypertension, and elevated fasting glucose — that together significantly increase the risk of type 2 diabetes, cardiovascular disease, and all-cause mortality. Metabolic syndrome affects approximately 30–40% of adults in Western countries and accelerates biological aging.

A biguanide drug that has been a first-line treatment for type 2 diabetes for over 60 years. Its primary mechanism is inhibition of mitochondrial complex I, leading to AMPK activation. Beyond glucose-lowering, metformin has demonstrated anti-aging effects in model organisms and epidemiological studies in diabetics. The TAME trial (Targeting Aging with Metformin) is a landmark multi-center study testing whether metformin delays age-related disease in non-diabetic adults.

The addition of a methyl group (–CH₃) to DNA, typically at cytosine bases in CpG dinucleotides, catalyzed by DNA methyltransferases (DNMTs). DNA methylation is the most studied epigenetic modification and serves as the basis for all major epigenetic clocks. Methylation patterns change systematically with age: some sites gain methylation (hypermethylation) while others lose it (hypomethylation), collectively providing the epigenetic clock signal.

The electrochemical gradient across the inner mitochondrial membrane (typically −140 to −180 mV in healthy cells), generated by the electron transport chain. This potential drives ATP synthesis via ATP synthase and is a critical indicator of mitochondrial function and health. Collapse of membrane potential leads to mitophagy initiation, and chronically depolarized mitochondria contribute to energy deficits and increased ROS in aging.

A selective form of autophagy that specifically targets damaged or dysfunctional mitochondria for degradation. Mitophagy is essential for maintaining mitochondrial quality and is regulated by the PINK1-Parkin pathway. Impaired mitophagy leads to accumulation of dysfunctional mitochondria, increased ROS production, and is strongly implicated in neurodegeneration and aging.

Methylenetetrahydrofolate reductase — an enzyme encoded by the MTHFR gene that is critical for folate metabolism and the methionine cycle, which produces S-adenosylmethionine (SAM), the universal methyl donor for DNA methylation. Common variants (C677T, A1298C) reduce enzyme activity by 30–70%, potentially impairing DNA methylation and homocysteine clearance. Elevated homocysteine from MTHFR variants is linked to cardiovascular disease and cognitive decline.

Mechanistic target of rapamycin — a serine/threonine kinase that acts as a central hub integrating nutrient, energy, and growth factor signals to regulate cell growth, protein synthesis, and autophagy. mTORC1 (complex 1) is the primary longevity-relevant complex; its chronic activation suppresses autophagy and promotes anabolic processes linked to accelerated aging. Inhibition of mTOR is one of the most robust interventions to extend lifespan across species.

A pharmacological or dietary strategy to reduce mTORC1 signaling with the goal of promoting autophagy, reducing cellular growth and senescence, and extending healthy lifespan. Pharmacological inhibitors include rapamycin and its rapalogs. Dietary approaches that inhibit mTOR include caloric restriction, protein restriction, and time-restricted eating. mTOR inhibition extends lifespan in every model organism tested.

A TGF-β family member secreted primarily by skeletal muscle that negatively regulates muscle growth and differentiation. Natural loss-of-function mutations in myostatin cause dramatic muscle hypertrophy in animals and humans. Myostatin levels tend to increase with age and contribute to sarcopenia; it is an active target for therapies aimed at preserving muscle mass in aging.

Nicotinamide adenine dinucleotide — a coenzyme found in all living cells that is essential for energy metabolism (as an electron carrier in redox reactions) and as a substrate for sirtuins and PARP enzymes. NAD+ levels decline markedly with age, contributing to impaired mitochondrial function, reduced sirtuin activity, and decreased DNA repair capacity. Precursors such as NMN and NR are widely used to boost NAD+ levels.

A potent BCL-2/BCL-XL inhibitor originally developed as a cancer drug that has been identified as one of the most effective senolytics. Navitoclax directly targets the pro-survival machinery that senescent cells depend on and has demonstrated remarkable senolytic efficacy in preclinical models. Its clinical use for aging is limited by dose-dependent thrombocytopenia (platelet reduction), but modified versions and targeted delivery approaches are in development.

Nuclear factor kappa-light-chain-enhancer of activated B cells — a master transcription factor that orchestrates innate immune responses and inflammation. NF-κB is chronically activated in aged tissues, contributing to 'inflammaging' — the low-grade sterile inflammation that drives many age-related diseases. SIRT1 and AMPK both negatively regulate NF-κB, providing molecular links between metabolic state and inflammation.

Nicotinamide mononucleotide — a naturally occurring precursor to NAD+ that is produced endogenously from nicotinamide riboside (NR) and taken orally as a supplement to boost NAD+ levels. NMN enters cells via the Slc12a8 transporter (in mice) and is converted to NAD+ by NMNAT enzymes. Clinical trials have confirmed that NMN supplementation raises blood NAD+ levels in humans; functional longevity benefits in humans are still being established.

An imbalance between the production of reactive oxygen species (ROS) and the cell's antioxidant defense capacity, resulting in cumulative oxidative damage to DNA, proteins, and lipids. Oxidative stress increases with age due to mitochondrial dysfunction, reduced antioxidant enzyme activity, and chronic inflammation. It is a central mechanism linking metabolic dysfunction to accelerated cellular aging.

A cyclin-dependent kinase inhibitor (encoded by CDKN2A) that enforces cell cycle arrest by inhibiting CDK4/6-Rb phosphorylation. p16 is a primary marker and mediator of cellular senescence. Its expression increases dramatically with age in multiple tissues and serves as a direct readout of senescent cell burden. p16+ cell accumulation is a hallmark of aging and is targeted by senolytic therapies.

A cyclin-dependent kinase inhibitor (encoded by CDKN1A) that is a key downstream effector of p53 in the DNA damage response. p21 enforces cell cycle arrest to allow time for DNA repair or, if damage is irreparable, promote senescence. While p21 mediates protective senescence induction, its chronic upregulation in aged tissues contributes to stem cell exhaustion and impaired regeneration.

A tumor suppressor transcription factor (encoded by TP53) often called the 'guardian of the genome.' p53 is activated by DNA damage, oncogenic stress, and oxidative stress, and can trigger cell cycle arrest, DNA repair, senescence, or apoptosis depending on the level and context of damage. Mutations in p53 are found in over half of human cancers, and its activity must be carefully balanced between tumor suppression and promotion of aging.

The maintenance of a healthy, functional protein pool (proteome) within cells. It encompasses protein synthesis, folding, trafficking, and degradation via the ubiquitin-proteasome system and autophagy. Proteostasis declines with age, leading to accumulation of misfolded and aggregated proteins — a hallmark of Alzheimer's, Parkinson's, and other age-related diseases.

A flavonoid polyphenol found abundantly in onions, capers, and apples that exhibits senolytic, anti-inflammatory, and antioxidant properties. Quercetin acts as a senolytic by inhibiting PI3K, which senescent cells rely on for survival signaling. As part of the dasatinib + quercetin (D+Q) combination, it is the most clinically advanced senolytic protocol. Quercetin also inhibits SASP-driving NF-κB signaling.

A macrolide compound produced by Streptomyces hygroscopicus that binds FKBP12 and allosterically inhibits mTORC1. Rapamycin was the first drug shown to extend lifespan in mammals when started late in life (NIA ITP study, 2009). It is FDA-approved as an immunosuppressant and anti-rejection drug. At lower ('geroscience') doses, rapamycin is being explored as a longevity intervention in healthy humans, with ongoing trials examining safety and efficacy.

Chemically reactive molecules containing oxygen — including superoxide (O₂⁻), hydrogen peroxide (H₂O₂), and hydroxyl radicals (•OH) — produced primarily as byproducts of mitochondrial respiration. At low levels, ROS function as signaling molecules (e.g., in hormesis and exercise adaptation); at high levels, they cause oxidative damage to DNA, proteins, and lipids. Chronic elevated ROS is a driver of cellular aging and age-related disease.

A naturally occurring stilbene polyphenol found in grape skins, red wine, and berries that became the subject of intense longevity research after it was reported to activate SIRT1 and mimic caloric restriction. While resveratrol clearly activates SIRT1 in the presence of fluorescent substrates, its direct SIRT1 activation in physiologically relevant contexts remains debated. Large human RCTs have largely not demonstrated consistent benefit, but research on more bioavailable formulations (e.g., pterostilbene) continues.

A state of permanent cell cycle arrest that a cell enters in response to DNA damage, oncogene activation, oxidative stress, or telomere shortening. Senescent cells resist apoptosis and secrete a pro-inflammatory cocktail of cytokines, proteases, and growth factors known as the senescence-associated secretory phenotype (SASP). Accumulation of senescent cells is a central driver of age-related inflammation and tissue dysfunction.

A class of drugs or compounds that selectively eliminate senescent cells by exploiting their resistance to apoptosis. Senolytics target pro-survival pathways (BCL-2/BCL-XL, PI3K/AKT) that senescent cells upregulate to avoid cell death. The dasatinib + quercetin combination is the most studied senolytic regimen in humans, with clinical trials ongoing for multiple age-related conditions including frailty, IPF, and chronic kidney disease.

Sirtuin 1 — the founding and most studied member of the sirtuin family of NAD+-dependent deacetylases. SIRT1 deacetylates and thereby regulates hundreds of targets including p53, FOXO3, NF-κB, and PGC-1α, broadly promoting stress resistance, DNA repair, metabolic efficiency, and mitochondrial biogenesis. SIRT1 activity is NAD+-dependent and declines with age as NAD+ levels fall.

A family of seven NAD+-dependent protein deacylases (SIRT1–7) with diverse subcellular localizations and substrates. SIRT1, SIRT6, and SIRT7 are nuclear; SIRT3, SIRT4, and SIRT5 are mitochondrial; SIRT2 is cytoplasmic. Collectively they regulate metabolism, DNA repair, inflammation, and stress responses. All require NAD+ as a co-substrate, directly linking cellular energy status to epigenetic and proteomic regulation.

Single nucleotide polymorphism — a variation at a single position in the DNA sequence among individuals. SNPs are the most common form of genetic variation in the human genome (approximately 4–5 million per person). GWAS (genome-wide association studies) use SNPs to identify associations between genetic variants and traits like disease risk or longevity. Notable longevity-associated SNPs are found in FOXO3, APOE, CETP, and telomere maintenance genes.

A naturally occurring polyamine found in high concentrations in wheat germ, aged cheese, mushrooms, and soy products that is a potent autophagy inducer. Spermidine inhibits the EP300 acetyltransferase, leading to histone hypoacetylation and upregulation of autophagy genes. Observational studies link higher dietary spermidine intake to reduced all-cause and cardiovascular mortality; clinical trials are ongoing for cognitive aging.

The progressive decline in the number and regenerative capacity of adult stem cells that occurs with aging. Stem cell exhaustion impairs tissue repair and regeneration in organs such as muscle, blood, gut, and brain. It is considered one of the hallmarks of aging, driven by accumulated DNA damage, epigenetic changes, and a deteriorating stem cell niche.

A ribonucleoprotein enzyme that extends telomeres by adding TTAGGG repeats to chromosome ends, counteracting replicative shortening. High telomerase activity in stem cells and germ cells maintains telomere length; most somatic cells have very low expression. Telomerase reactivation is being studied as a potential anti-aging strategy, but must be carefully regulated to avoid promoting cancer.

Repetitive DNA sequences (TTAGGG in humans) that cap the ends of chromosomes and protect them from degradation and fusion. Telomeres shorten with each cell division and with oxidative stress. Critically short telomeres trigger DNA damage responses leading to senescence or apoptosis. Average telomere length is widely used as a biomarker of cellular aging and is associated with risk of age-related disease.

Inherited genetic variants that influence baseline telomere length. Several common SNPs in genes such as TERT, TERC, OBFC1, and RTEL1 are strongly associated with telomere length variation between individuals. These polymorphisms explain approximately 25–50% of the heritable variation in telomere length and are associated with risk of cancer, cardiovascular disease, and age-related diseases in GWAS studies.

The primary androgen hormone in males (also present at lower levels in females) that promotes muscle protein synthesis, bone density, libido, red blood cell production, and cognitive function. Total testosterone declines approximately 1–2% per year after age 30 in men. Low testosterone is associated with metabolic syndrome, cardiovascular disease, depression, and reduced quality of life.

The thyroid gland produces two main hormones — thyroxine (T4) and triiodothyronine (T3) — that regulate basal metabolic rate, thermogenesis, heart rate, and cellular energy use. Hypothyroidism (low thyroid) causes fatigue, weight gain, and cognitive slowing; hyperthyroidism accelerates metabolism and increases oxidative stress. Optimal thyroid function is critical for metabolic health and longevity.

An eating pattern that confines all caloric intake to a defined daily window (typically 8–12 hours), extending the overnight fast. Time-restricted eating synchronizes food intake with circadian biology and, without explicit caloric restriction, can improve metabolic markers, reduce inflammation, promote autophagy, and improve cardiometabolic risk factors. Protocols commonly studied include 16:8 (16 hours fasting, 8 hours eating) and 18:6.

The maximum rate of oxygen consumption during incremental exhaustive exercise, expressed as mL O₂/kg/min. VO2 max is the gold standard measure of cardiorespiratory fitness and is one of the strongest predictors of all-cause mortality — independent of other risk factors. It declines approximately 10% per decade after 30, but is highly trainable. Low VO2 max is a stronger mortality predictor than smoking, hypertension, or diabetes.

Aerobic exercise performed at an intensity corresponding to approximately 65–75% of maximum heart rate (or the highest intensity at which one can still hold a conversation), primarily utilizing the aerobic oxidative metabolism pathway. Zone 2 training is the most effective modality for increasing mitochondrial density, improving metabolic flexibility, enhancing fat oxidation, and raising VO2 max over time. It is considered by many longevity physicians as the most important exercise type for healthy aging.