Aging. The progressive loss of function over time, visible as rising risk of disease and death with each year.
Autophagy and mitophagy. The cell's recycling process for damaged components, and the version that specifically clears worn-out mitochondria. Fasting and exercise stimulate both.
Epigenetic clock. An algorithm that estimates biological age from DNA methylation patterns. Useful at the population level; still noisy for individuals.
Epigenome. The chemical marks (such as DNA methylation) layered on the genome that control which genes are active. They drift with age and are the basis of epigenetic clocks.
Extracellular matrix. The scaffolding between cells. Its stiffening and cross-linking with age has been proposed as an additional hallmark.
Geroscience. The study of aging as the common root of chronic disease, and of interventions that target it directly.
Hallmarks of aging. The twelve interconnected processes researchers use to organize the causes of aging, from genomic instability to dysbiosis.
Hayflick limit. The number of times a normal human cell can divide before it becomes senescent, roughly 40–60.
Healthspan. The years lived in good health and independence. Usually shorter than lifespan; closing that gap is the goal.
Heterochronic parabiosis. Surgically joining the circulation of a young and an old animal to study blood-borne aging factors.
Immunosenescence. The age-related decline of the immune system, which makes infections more dangerous and vaccines less effective.
Inflammaging. The chronic, low-grade, body-wide inflammation that rises with age and drives most age-related disease.
Lifespan. How long an organism lives. Average lifespan is life expectancy; maximum lifespan is the oldest any member of the species has reached.
Mitochondria. The organelles that turn fuel into energy. Their efficiency falls with age; zone 2 training is the best-known way to rebuild it.
Partial reprogramming. Briefly expressing the Yamanaka factors (OSK or OSKM) to reset a cell's epigenetic age without erasing its identity. In its first human trial as of 2026.
Proteostasis. The balance of making, folding, and clearing proteins. Its decline leads to the protein clumps seen in Alzheimer's and Parkinson's.
Reactive oxygen species and oxidative stress. Chemically reactive byproducts of metabolism and the damage they cause when they outrun the body's antioxidant defenses.
SASP. Senescence-associated secretory phenotype: the cocktail of inflammatory molecules senescent cells release, harming neighboring tissue.
Senescence. The gradual deterioration of function with age. "Cellular senescence" is the specific state in which damaged cells stop dividing but stay alive and secrete inflammatory signals.
Senolytics. Drugs or compounds that selectively kill senescent cells. Dasatinib plus quercetin and fisetin are the best known; human evidence is early.
Stem cells. Cells that can renew themselves and become other cell types. Their exhaustion with age slows tissue repair.
Telomeres and telomerase. Protective caps on the ends of chromosomes that shorten with each cell division, and the enzyme that can rebuild them.
AMPK. An energy sensor activated by exercise and low fuel that switches cells toward repair and fat burning. Metformin acts partly through it.
Amyloid beta and tau. The two proteins that aggregate in the Alzheimer's brain.
FGF-21. A fasting hormone from the liver involved in fat metabolism; it extends lifespan in mice.
FOXO. Transcription factors that turn on stress-resistance and repair genes; the worm version (DAF-16) was among the first longevity genes discovered.
Insulin and IGF-1. Growth-promoting hormones. Lower signaling through this axis extends lifespan in worms, flies, and mice; in humans the picture is more complicated.
Insulin resistance. When cells stop responding normally to insulin, forcing higher levels to control blood sugar. The first step toward type 2 diabetes, detectable years earlier via fasting insulin.
Klotho. A protein whose levels fall with age; more of it extends life in mice and is linked to better cognition in humans.
Lactate. A fuel produced during exercise, not a waste product. Its concentration in blood marks the two training thresholds.
mTOR. Mechanistic target of rapamycin: a nutrient-sensing pathway that promotes growth when food is plentiful. Inhibiting it (rapamycin, fasting) extends lifespan in every organism tested.
Myokines and exerkines. Signaling molecules released by muscle, especially during exercise, that act on the brain, liver, fat, and bone. Part of why exercise is a whole-body drug.
NAD+. A coenzyme central to energy metabolism and DNA repair that declines with age. NMN and NR raise its blood levels; clinical benefit is unproven.
p53. The "guardian of the genome," a protein that halts division or triggers death in damaged cells.
Sirtuins. A family of NAD+-dependent proteins involved in DNA repair and metabolism. The target resveratrol was supposed to activate.
Age-related macular degeneration. The leading cause of vision loss in older adults.
Aging-associated diseases. Conditions for which age is the dominant risk factor: atherosclerotic disease, cancer, neurodegeneration, type 2 diabetes, osteoporosis, and others.
Alpha-1 antitrypsin deficiency. An inherited shortage of a protein that protects the lungs and liver. It causes early COPD, especially in smokers, and is found with a one-time blood test.
Asthma. Long-term inflammation that narrows the airways in episodes of wheeze, cough, and breathlessness. Good control with inhaled steroids prevents attacks and lasting damage.
Atherosclerosis. The buildup of cholesterol-rich plaque in artery walls, driven by ApoB particles over decades. The cause of most heart attacks and strokes.
Atrial fibrillation. An irregular, often rapid heart rhythm that raises the risk of stroke about fivefold if untreated.
Barrett's esophagus. A change in the lining of the lower esophagus caused by years of acid reflux. It raises the risk of esophageal cancer and is found by upper endoscopy.
Benign prostatic hyperplasia (BPH). Non-cancerous enlargement of the prostate with age, which can weaken the urine stream and cause frequent urination at night.
BRCA1 and BRCA2. Genes whose harmful variants sharply raise the risk of breast, ovarian, prostate, and pancreatic cancer.
Cardiovascular-kidney-metabolic syndrome. The American Heart Association's 2023 framing of obesity, diabetes, kidney disease, and heart disease as one connected condition.
Celiac disease. An autoimmune reaction to gluten that damages the small intestine. Diagnosed with a blood test and confirmed with a biopsy, both while still eating gluten.
Chronic kidney disease. Kidney damage or reduced filtering that lasts at least three months, measured with eGFR and urine albumin. Usually silent until advanced.
COPD. Chronic obstructive pulmonary disease: emphysema and chronic bronchitis, which narrow the airways and cannot be fully reversed. Diagnosed by spirometry.
Delirium. A sudden, fluctuating state of confusion and poor attention, common in older adults in hospital or after surgery. Often preventable, and linked to faster cognitive decline.
Dementia and cognitive reserve. Cognitive decline severe enough to interfere with daily life, and the brain's capacity (built by education, activity, and connection) to compensate for damage before symptoms show.
Diverticular disease. Small pouches in the colon wall (diverticulosis) that can become inflamed (diverticulitis). Fiber helps prevent flares; nuts and seeds do not cause them.
Endometriosis. Tissue similar to the lining of the uterus growing outside it, causing pelvic pain and infertility. It affects about 1 in 10 women of reproductive age.
Erectile dysfunction. Trouble getting or keeping an erection. It often appears years before heart disease, because both stem from damaged blood vessels.
Familial hypercholesterolemia. An inherited condition, in roughly 1 in 250 to 300 people, that causes very high LDL cholesterol from birth.
Frailty. A state of reduced reserve in which small insults (a fall, a flu) cause outsized harm. Measured with tools such as the Fried phenotype or the Clinical Frailty Scale, and partly reversible with exercise and protein.
GERD. Gastroesophageal reflux disease: stomach acid flowing back into the esophagus often enough to cause heartburn or damage.
H. pylori. A bacterium that infects the stomach lining and causes most ulcers and stomach cancers. Found with a breath or stool test and cured with antibiotics.
Hypertension. Blood pressure that stays at or above 130/80 mm Hg, under current US guidelines.
Inflammatory bowel disease (IBD). Crohn's disease and ulcerative colitis: chronic, immune-driven inflammation of the gut. Different from IBS.
Insomnia disorder. Trouble falling or staying asleep at least three nights a week for three months or more, with daytime consequences.
Irritable bowel syndrome (IBS). Recurring belly pain with changes in bowel habits, without visible damage to the gut. Diagnosed by its symptoms once warning signs are ruled out.
Li-Fraumeni syndrome. A rare inherited TP53 mutation with a very high lifetime risk of cancer, and one of the few groups for whom whole-body MRI screening is recommended.
Lynch syndrome. An inherited condition that raises the risk of colorectal, endometrial, and several other cancers, and calls for earlier, more frequent colonoscopy.
MASLD. Metabolic dysfunction-associated steatotic liver disease: the name, since 2023, for fatty liver disease linked to excess weight, insulin resistance, or related risks. Its inflammatory form is MASH.
Metabolic syndrome. A cluster of abdominal obesity, high blood pressure, high glucose, high triglycerides, and low HDL that multiplies cardiovascular risk.
Neurodegenerative disease. Progressive loss of neurons, as in Alzheimer's, Parkinson's, and ALS.
Obstructive sleep apnea. Repeated airway collapse during sleep, causing oxygen drops and fragmented sleep. Common, underdiagnosed, and a driver of hypertension and atrial fibrillation.
Osteopenia. Bone density below normal but above the osteoporosis threshold, a T-score between −1 and −2.5.
Osteoporosis. Loss of bone density that makes fractures likely. Measured by DEXA; prevented by loading the skeleton.
Pelvic floor disorders. Leaking urine, pelvic organ prolapse, and related problems from weak or overactive pelvic floor muscles. Common after childbirth and treatable with physical therapy.
Polycystic ovary syndrome (PCOS). A common hormonal and metabolic condition with irregular periods, high androgens, or many small follicles on the ovaries. Renamed polyendocrine metabolic ovarian syndrome (PMOS) in 2026.
Polypharmacy. Taking five or more medicines regularly, which raises the risk of interactions, falls, and hospital stays.
Prediabetes. Blood sugar above normal but below diabetes: a fasting glucose of 100–125 mg/dL or an HbA1c of 5.7–6.4%.
Preeclampsia. High blood pressure with signs of organ strain that begins after 20 weeks of pregnancy. It marks a higher lifelong risk of heart disease.
PRISm. Preserved ratio impaired spirometry: a normal FEV1-to-FVC ratio with a low FEV1. It signals a higher risk of COPD and of heart and metabolic disease.
Sarcopenia. The age-related loss of muscle mass and strength. The main driver of frailty.
Type 2 diabetes. Chronically high blood sugar from insulin resistance and eventual insulin deficiency. Largely preventable with weight, diet, and exercise.
AMH. Anti-Müllerian hormone, a blood test that reflects how many eggs remain in the ovaries. Useful for planning egg freezing or IVF; it does not predict the chance of natural conception.
Apnea-hypopnea index (AHI). Breathing pauses and shallow-breathing episodes per hour of sleep. Five or more defines sleep apnea; 30 or more is severe.
ApoB. Apolipoprotein B, one molecule per atherogenic particle. The most direct blood measure of atherosclerotic risk.
Biomarker. Any measurable indicator of a biological state, from a blood test to a scan to a fitness test.
Breast density. How much of the breast is dense tissue on a mammogram. Dense breasts make cancers harder to see and modestly raise risk.
Continuous glucose monitor (CGM). A wearable sensor that reads interstitial glucose every few minutes.
Coronary artery calcium (CAC) scan. A CT scan that scores calcified plaque in the heart's arteries.
CT angiography. A contrast CT that images the coronary arteries, including soft plaque.
Cystatin C. A blood protein used to estimate kidney function that, unlike creatinine, is barely affected by muscle mass.
DEXA. Dual-energy X-ray absorptiometry: a low-dose scan that measures bone density, lean mass, and fat distribution.
DFA alpha 1. A nonlinear HRV index that drops toward 0.75 around the aerobic threshold.
Diffusion-weighted imaging. An MRI technique that highlights densely packed cells; whole-body MRI uses it to flag possible tumors.
Echocardiogram. An ultrasound of the heart's structure and function.
Effective dose (mSv). The standard measure of radiation exposure from imaging, in millisieverts. Natural background radiation is about 3 mSv a year in the US.
eGFR. Estimated glomerular filtration rate: how well the kidneys filter blood, calculated from creatinine and ideally cystatin C.
Elastography. An ultrasound-based measurement of liver stiffness, a marker of scarring. FibroScan is the best-known brand.
Ferritin. The body's iron store; also rises with inflammation.
FEV1 and FVC. The air you can blow out in the first second (FEV1) and in total (FVC) during spirometry. A low ratio between them means the airways are narrowed.
FFMI and ALMI. Fat-free mass index and appendicular lean mass index: your total lean mass, and the lean mass of your arms and legs, divided by height squared, both measured by DEXA. Low ALMI is one criterion for sarcopenia.
FIB-4. A score calculated from age, two liver enzymes, and platelet count that estimates the chance of advanced liver scarring.
HbA1c. Glycated hemoglobin, a three-month average of blood glucose.
Heart rate variability (HRV). Beat-to-beat variation in heart rhythm, a window into the autonomic nervous system and recovery.
HOMA-IR. An insulin-resistance index calculated from fasting glucose and fasting insulin.
Homocysteine. An amino acid that rises with B-vitamin deficiency and tracks with vascular risk.
hs-CRP. High-sensitivity C-reactive protein, a general marker of inflammation and cardiovascular risk.
IL-6 and TNF-alpha. Inflammatory cytokines used in research to measure inflammaging.
Incidentaloma. An unexpected finding on a scan done for another reason. Most are harmless, but each can trigger more tests.
LDL-C and HDL-C. The cholesterol carried in low- and high-density lipoproteins. LDL-C is causal for heart disease; HDL-C is a marker, not a target.
Lipoprotein(a). A genetically determined, LDL-like particle that independently raises cardiovascular risk. Measured once; no approved drug lowers it yet.
Low-dose CT. A CT scan using a fraction of standard radiation, used for yearly lung cancer screening in people with a heavy smoking history.
Multi-cancer early detection test. A blood test that looks for DNA shed by many kinds of cancer at once. Galleri is the best known; none yet has proof that it saves lives.
Polysomnography. An overnight sleep study that records brain waves, breathing, oxygen, and movement; the gold standard for diagnosing sleep disorders.
PREVENT equations. The American Heart Association's 2023 calculator for 10- and 30-year cardiovascular risk, which adds kidney and metabolic measures to the classic risk factors.
PSA. Prostate-specific antigen, a blood test used in prostate cancer screening. Cancer raises it, but so do enlargement and inflammation.
p-tau217. A form of the tau protein measurable in blood that closely tracks Alzheimer's disease changes in the brain.
Semen analysis. A lab test of sperm count, movement, and shape, and the starting point for checking male fertility.
Spirometry. A breathing test in which you blow out as hard and as long as you can into a tube. It diagnoses COPD and asthma and tracks lung function over time.
Triglycerides. Fat in the blood. High fasting levels signal insulin resistance and excess refined carbohydrate or alcohol.
T-score. How your bone density compares with a healthy young adult's, in standard deviations. A T-score of −2.5 or lower defines osteoporosis.
Upper endoscopy. A camera on a flexible tube passed through the mouth to examine the esophagus, stomach, and duodenum, used to look for Barrett's esophagus, ulcers, and stomach cancer.
Urine albumin-to-creatinine ratio (uACR). A urine test for protein leaking from the kidneys, an early sign of kidney and blood vessel damage.
VO2 max. The maximum rate of oxygen your body can use during exercise, in ml/kg/min. The strongest single predictor of longevity we can measure.
Whole-body MRI. An MRI of most of the body in one session, sold for screening by companies such as Prenuvo and Ezra. Proof of benefit for people at average risk is lacking.
Caloric restriction. Eating substantially less than maintenance without malnutrition. The oldest lifespan intervention.
Calorie. A unit of food energy. Needs vary with size, age, sex, and activity.
Fasting-mimicking diet. A five-day, low-calorie, mostly plant-based eating plan designed to reproduce some effects of fasting while still eating.
Fiber. Indigestible plant carbohydrate that feeds the microbiome, slows glucose, and lowers cholesterol.
Glycemic index and postprandial glucose. How fast a food raises blood sugar, and the actual rise after a meal.
Ketosis. A metabolic state, reached by fasting or very low carbohydrate intake, in which the liver makes ketones from fat for fuel.
Low-FODMAP diet. A short-term elimination diet that cuts fermentable carbohydrates and then reintroduces them one at a time to find IBS triggers. Best done with a dietitian.
Macronutrients. Protein, carbohydrate, and fat. Micronutrients are the vitamins and minerals.
Microbiome. The trillions of microbes in the gut and elsewhere that shape digestion, immunity, and glucose response.
Nova classification. A system that sorts foods by how processed they are, from unprocessed (group 1) to ultra-processed (group 4).
Omega-3 and omega-6. Two families of polyunsaturated fat. Omega-3s (EPA, DHA) come from fish; omega-6 (linoleic acid) from seed oils and nuts. Both are essential.
Probiotics. Live microbes sold as supplements. Benefits are specific to the strain and the condition, and most healthy people gain little from them.
Refeeding syndrome. A dangerous electrolyte shift when food is reintroduced after prolonged fasting or starvation.
Saturated, monounsaturated, and polyunsaturated fat. Fats classified by their chemical bonds. Saturated (butter, red meat) raises LDL; monounsaturated (olive oil) and polyunsaturated (fish, seed oils) lower it.
Time-restricted eating. Confining food to a daily window, typically 8–12 hours.
Trans fat. Industrially hardened fat that raises LDL and lowers HDL. Banned from the US food supply.
Ultra-processed food. Industrial formulations of refined ingredients and additives (the Nova group 4). Linked to most chronic diseases.
Aerobic threshold (LT1, VT1). The intensity at which blood lactate first rises above resting, around 2 mmol/L. The top of zone 2.
Anaerobic threshold (LT2, VT2, OBLA). The intensity at which lactate accumulates rapidly, around 4 mmol/L. The boundary between hard and very hard.
Compound lift. An exercise that moves several joints at once: squat, deadlift, press, row, carry.
Dynamic and static stretching. Moving through a range of motion versus holding a position. Dynamic before training, static after.
Grip strength. A simple measure of overall strength that predicts mortality remarkably well.
Heart rate reserve. Maximum heart rate minus resting heart rate; the basis of some zone formulas.
High-intensity interval training (HIIT). Repeated hard efforts with recovery between them. The "Norwegian 4×4" is the best-studied protocol for VO2 max.
Hypertrophy. Growth in muscle size.
MET. Metabolic equivalent: a multiple of resting energy expenditure used to express exercise intensity and fitness.
One-leg stand test. Standing on one leg for 10 seconds without support. Failing it in midlife is linked to a higher risk of death.
Periodization. Organizing training into phases with different goals to keep improving and avoid overtraining.
Polarized training. Spending roughly 80% of training time easy and 20% hard, with little in between.
Progressive overload. Gradually increasing the load, reps, or volume so muscle keeps adapting.
Sit-rise test. Sitting on the floor and standing back up with as little support as possible, scored out of 10. Higher scores predict lower mortality.
Talk test. The hardest pace at which you can still speak in full sentences, a reliable proxy for the first ventilatory threshold.
Zone 2. Steady exercise just below the aerobic threshold, where fat oxidation and mitochondrial adaptation are maximized.
Acarbose. An alpha-glucosidase inhibitor that slows starch digestion. A robust ITP result.
ACE inhibitors and ARBs. Blood pressure drugs that act on the renin-angiotensin system.
ARIA. Amyloid-related imaging abnormalities: brain swelling or small bleeds caused by anti-amyloid Alzheimer's drugs, more common in APOE4 carriers.
Beers Criteria. The American Geriatrics Society's list of medicines that are often inappropriate for adults 65 and older, last updated in 2023.
Colchicine. An old gout drug approved in low dose in 2023 for cardiovascular prevention in people with heart disease.
Creatine. A compound that recycles cellular energy in muscle and brain; the best-evidenced sports supplement.
Deprescribing. Planned tapering or stopping of medicines whose harms now outweigh their benefits, done with a clinician.
DSHEA. The 1994 US law that lets dietary supplements be sold without first proving they are safe or effective.
Ezetimibe and bempedoic acid. Non-statin LDL-lowering drugs that block absorption and upstream synthesis respectively.
Geroprotector. A drug intended to slow aging itself rather than treat one disease.
GLP-1 receptor agonists. Semaglutide, tirzepatide, and relatives: hormone mimics that reduce appetite and glucose, producing large weight loss and cardiovascular benefit.
Inclisiran. A twice-yearly injection that silences PCSK9 production in the liver to lower LDL cholesterol.
Lecanemab and donanemab. Antibody drugs that clear amyloid from the brain and modestly slow early Alzheimer's disease, with a risk of ARIA.
Menopausal hormone therapy. Estrogen, with a progestogen for anyone who has a uterus, used to treat menopause symptoms and prevent bone loss.
Metformin. The first-line diabetes drug, a biguanide, once hoped to be a longevity drug.
NMN and NR. Nicotinamide mononucleotide and nicotinamide riboside, precursors that raise NAD+ levels.
PCSK9 inhibitors. Injectable antibodies (or an siRNA) that lower LDL by about 60% by keeping LDL receptors active.
Proton pump inhibitors (PPIs). The strongest acid-reducing drugs, such as omeprazole and pantoprazole. Effective for reflux and ulcers; long-term daily use deserves a yearly review.
Psyllium. A soluble fiber from the Plantago plant that lowers LDL and post-meal glucose.
Rapamycin (sirolimus). An mTOR inhibitor and the most robust lifespan-extending drug in mice. Used off-label for longevity at low weekly doses; unproven in humans.
Semaglutide. A GLP-1 receptor agonist (Ozempic, Wegovy) available as a weekly injection or a daily pill.
SGLT2 inhibitors. Diabetes drugs that make the kidneys excrete glucose; they also protect the heart and kidneys.
Statins. Drugs that lower LDL by blocking cholesterol synthesis in the liver.
Testosterone replacement therapy. Treatment for men with consistently low testosterone and symptoms of deficiency. It is not an anti-aging therapy.
Third-party certification. Independent testing, such as NSF Certified for Sport or USP Verified, that a supplement contains what its label says and no contaminants.
Tirzepatide. A weekly injection (Mounjaro, Zepbound) that activates both GLP-1 and GIP receptors, producing about 20% average weight loss in trials.
Air quality index (AQI). The EPA's 0–500 scale for daily air pollution. Above 100 is unhealthy for sensitive groups; above 150 is unhealthy for everyone.
CBT-I. Cognitive behavioral therapy for insomnia: a structured program of sleep scheduling and habit and thought changes, and the first-line treatment for chronic insomnia.
Chronotype. Your natural preference for earlier or later sleep times, which is partly genetic and shifts with age.
Circadian rhythm. The body's roughly 24-hour internal clock, set mainly by light, that times sleep, hormones, and metabolism.
Cognitive behavioral therapy. A structured talk therapy that changes unhelpful patterns of thinking and behavior; a first-line treatment for depression and anxiety.
Microplastics and nanoplastics. Plastic fragments smaller than 5 millimeters, and smaller than 1 micrometer, now found in food, water, and human tissue. Their health effects are not yet known.
Mindfulness. Paying deliberate, nonjudgmental attention to the present moment; the basis of many meditation programs.
PFAS. So-called forever chemicals used in nonstick, stain-resistant, and waterproof products. They persist for years in the body and the environment.
PM2.5. Airborne particles 2.5 micrometers across or smaller, from combustion and wildfire smoke, that reach deep into the lungs and bloodstream.
Radon. A colorless, odorless radioactive gas that seeps from the ground into homes; the second leading cause of lung cancer in the US.
Advance directive. Documents that name who makes medical decisions for you (a healthcare proxy) and record the care you would want if you could not speak for yourself.
Annual Wellness Visit. Medicare's yearly prevention-planning visit, covered without cost sharing. It is a planning conversation, not a physical exam.
Geriatrician. A doctor trained in the care of older adults, especially people with several conditions, many medicines, or frailty.
Hospice. Comfort-focused care for people with a life expectancy of six months or less who stop treatment aimed at curing their illness.
Palliative care. Specialist care that relieves symptoms and stress at any stage of a serious illness, and can run alongside treatment aimed at cure.
Prehabilitation. Exercise, nutrition, and a medication review in the weeks before surgery, to speed recovery and lower complications.
Pulmonary rehabilitation. Supervised exercise and education for people with COPD and other lung diseases, which improves breathing, fitness, and quality of life.
Absolute and relative risk. Absolute risk is your actual chance of an outcome; relative risk compares that chance between groups. Halving a 2% risk is a 50% relative reduction but a 1-point absolute one.
Confounding and reverse causation. When a third factor explains an association, or when the "outcome" is actually causing the "exposure" (sick people quitting alcohol, for example).
Double-blind and placebo. Neither participants nor researchers know who got the treatment; the control group gets an inert look-alike.
Hazard ratio. The relative rate of an event (such as death) in one group versus another over the study period.
Healthy-user effect. The tendency of people who do one healthy thing to do many, which makes observational studies overstate the benefit of any single habit.
Interventions Testing Program (ITP). The NIA's multi-site program that tests candidate compounds for lifespan extension in mice under rigorous, replicated conditions.
Kaplan-Meier curve. The standard plot of survival over time, used to compare lifespan between groups.
Mendelian randomization. Using genetic variants as natural experiments to test whether an exposure is causal.
Meta-analysis and umbrella review. A statistical pooling of many studies, and a review of many meta-analyses.
Model organisms. Yeast, worms, flies, mice, rats, dogs, and monkeys, used because they age faster and can be studied in controlled conditions.
Number needed to treat. How many people must take a treatment for one of them to benefit.
Observational (cohort) study. Follows people who chose their own exposures. Can show association, not causation, and is vulnerable to confounding.
Preclinical and clinical phases. Animal and lab work, then human trials in phases 1 (safety), 2 (dose and signal), and 3 (efficacy at scale).
Randomized controlled trial (RCT). Participants are randomly assigned to treatment or control, which lets a study show cause rather than association.
Retraction. The formal withdrawal of a published paper. Several studies cited in the first edition of this guide have since been retracted.
Surrogate endpoint. A lab value or scan used in place of an outcome people actually experience, such as LDL cholesterol instead of heart attacks.
UM-HET3 and C57BL/6 mice. The genetically diverse mouse strain used by the ITP, and the common inbred strain used in much other research.
USPSTF grades. The US Preventive Services Task Force grades preventive services from A to D, plus I for insufficient evidence. Most private insurance must cover A and B services without cost sharing.
