Concepts & Frameworks

Absolute risk (AR) is the probability that an individual experiences an event — such as a heart attack, cancer diagnosis, or death — within a defined time period. Relative risk…

Allostatic load is the cumulative physiological cost of adapting to chronic stressors, representing wear and tear on regulatory systems that maintain homeostasis through…

Antagonistic pleiotropy, formulated by evolutionary biologist George C. Williams in 1957, holds that genes selected for benefits early in life can cause harm later, after…

Biological age is an estimate of how old a person's body appears to be based on physiological and molecular markers, rather than the calendar. It can be derived from blood…

A caloric restriction mimetic (CR mimetic) is a compound that reproduces some molecular and physiological effects of caloric restriction — including AMPK activation, mTORC1…

A centenarian is a person who has reached the age of 100 years or more. Centenarians are a key research population in longevity science because they typically delay or escape…

Chronological age is the time elapsed since a person's birth, usually measured in years. It is the standard reference variable in demography, medicine and epidemiology and…

Compression of morbidity is a concept introduced by James Fries in 1980 describing a scenario in which the onset of chronic disease and disability is postponed faster than the…

Confounding is a distortion of the estimated association between an exposure and an outcome caused by a third variable — the confounder — that is independently associated with…

The Disability-Adjusted Life Year (DALY) is the cornerstone metric of the Global Burden of Disease framework, expressing population health loss as the sum of Years of Life Lost…

The disposable soma theory, proposed by Thomas Kirkwood in 1977, posits that organisms allocate finite metabolic resources between somatic maintenance and reproduction. Because…

Epigenetic drift describes the progressive, largely stochastic divergence of DNA methylation patterns between cells, tissues, and individuals as age advances. The landmark…

Frailty is a clinical state of increased vulnerability to stressors resulting from accumulated deficits across multiple physiological systems, leading to diminished reserve and…

The free radical theory of aging, proposed by Denham Harman in 1956, originally attributed aging to cumulative cellular damage from oxygen-derived free radicals, drawing on…

Gerontology is the scientific study of aging across biological, psychological, and social dimensions. Established as a formal discipline in the early 20th century, with Ilya…

A geroprotector is any drug, supplement, or lifestyle intervention targeting fundamental aging mechanisms to extend healthspan. Unlike disease-specific treatments, geroprotectors…

Geroscience is an interdisciplinary field that investigates the biological mechanisms of aging and their causal links to chronic disease. Coined around 2007 by researchers at the…

Gompertz law, formulated by the British actuary Benjamin Gompertz in 1825, describes the empirical observation that human mortality risk increases exponentially with adult age:…

HALE (Healthy Life Expectancy) is a WHO summary metric defined as the average number of years a person can expect to live in full health, adjusting total life expectancy downward…

A hazard ratio is the ratio of the instantaneous event rate in one group to that in a reference group at any given moment during follow-up, derived from a Cox…

Healthspan is the period of life spent in good health, free from serious chronic disease and major functional impairment. It is conceptually distinct from lifespan, which counts…

Heritability of lifespan is the proportion of variance in age at death attributable to additive genetic differences among individuals in a defined population. Classic twin-study…

The hyperfunction theory of aging, proposed by Mikhail Blagosklonny in 2006, holds that aging is driven by the continued overactivity of nutrient- and mitogen-sensing growth…

The Kaplan-Meier estimator is a nonparametric method for estimating the survival function S(t) — the probability of surviving beyond a given time t — from censored time-to-event…

Late-life mortality deceleration — the mortality plateau — is the observed phenomenon in which the age-specific hazard of death ceases its exponential Gompertz-law acceleration…

Lifespan is the total length of time an organism lives, from birth to death, typically expressed in years for humans. In population terms it is summarised by life expectancy at…

Longevity escape velocity describes a hypothetical threshold at which medical advances extend remaining life expectancy by more than one year per calendar year, effectively…

Maximum lifespan is the longest documented or theoretically possible age that a member of a species can reach under optimal conditions, distinct from average life expectancy…

Mendelian randomization (MR) uses germline genetic variants — typically single-nucleotide polymorphisms associated with an exposure in a genome-wide association study — as…

A meta-analysis is a statistical procedure that quantitatively synthesises results from multiple independent studies addressing the same research question, yielding a pooled…

Mortality doubling time (MDT) is the number of years it takes for age-specific mortality risk to double, derived directly from the Gompertz exponent b as MDT = ln(2)/b. In…

Multimorbidity is defined as the co-occurrence of two or more chronic conditions within the same person, without designating a primary or index disease — a distinction from the…

Mutation accumulation theory is an evolutionary explanation for senescence, first proposed by Peter Medawar in his 1952 lecture "An Unsolved Problem of Biology." It holds that…

Negligible senescence describes organisms that show no measurable functional decline, increase in mortality risk, or loss of reproductive capacity with chronological age. The…

The number needed to treat (NNT) is the average number of patients who must receive an intervention for one additional patient to benefit over control. Introduced by Laupacis,…

The oldest-old is a demographic and gerontological term for individuals aged 85 and above, the fastest-growing segment of most high-income country populations. This group shows…

Polypharmacy is conventionally defined as the concurrent use of five or more medications by one patient, though thresholds vary by definition (some use ≥4, hyperpolypharmacy…

A Quality-Adjusted Life Year (QALY) is one year of life weighted by health-related quality of life, where 1.0 represents one year in perfect health and 0 represents death…

A randomized controlled trial (RCT) is an experimental study design in which participants are allocated to an intervention or control condition through a chance-based process —…

The rate of living theory proposes that an organism's lifespan is inversely proportional to its mass-specific metabolic rate — the faster energy is consumed, the sooner the…

The reliability theory of aging, advanced by Leonid and Natalia Gavrilov in the early 1990s, applies engineering reliability mathematics to biological systems. It models…

In gerontology, physical resilience is operationally defined as the capacity to recover or maintain physical function after an acute health stressor - illness, surgery, fall,…

Successful aging is a gerontological framework introduced by John Rowe and Robert Kahn (1987, Science) and elaborated in 1997 (The Gerontologist), distinguishing usual aging -…

A supercentenarian is a person verified to have reached the age of 110 years or more. The 110+ threshold and term were popularized chiefly by L. Stephen Coles, founder of the…