Glossary

A

Age acceleration

The gap between a person's biological age, as estimated by a clock, and their age in years. If a clock says 65 for a 60-year-old, that person has five years of age acceleration. A negative gap means the body looks younger than its birth date.

Also: accelerated aging

Allostatic load

The cumulative “wear and tear” on the body from having to adapt to stress over long periods. Researchers estimate it by counting how many routine measurements, such as blood pressure, cholesterol, blood sugar and markers of inflammation, fall into a high-risk range. Different studies use different sets of measurements, so scores are not directly comparable.

AMPK

An enzyme that works as the cell's fuel gauge. When energy runs low, for example during exercise or fasting, AMPK switches on and tells the cell to burn stored fuel and to save energy elsewhere. Several drugs and diets studied for aging act on it.

Amyloid

A small protein fragment that can clump into sticky deposits (plaques) between nerve cells. Plaques are one of the two hallmarks of Alzheimer's disease, together with tangles of tau. Many people have plaques without ever developing dementia.

Also: amyloid-beta, beta-amyloid

Autophagy

Literally “self-eating”: the cell's recycling system. Worn-out proteins and damaged parts of the cell are wrapped up and delivered to lysosomes, where they are broken down and reused. Autophagy tends to slow down with age.

Also: autophagic

B

Biological age

How old the body seems from measurements, as opposed to how many years a person has lived. It is estimated with epigenetic clocks, blood proteins or other markers. Different clocks often disagree, so a biological age is an estimate, not a fact about a person.

Also: biological aging

Biomarker

Something that can be measured, usually in blood, urine or a scan, that indicates what is happening in the body: blood sugar for diabetes, for example. Researchers look for biomarkers of aging to test treatments without waiting decades.

Blinded

In a blinded study, participants (single-blind) or both participants and researchers (double-blind) don't know who received the real treatment. This stops expectations from colouring the results.

Also: double-blind, single-blind

C

Calorie restriction

Eating fewer calories than usual without becoming malnourished. In many laboratory animals it extends lifespan, which made it one of the most studied ideas in aging research. Evidence in people is limited to shorter trials of health markers.

Also: caloric restriction, dietary restriction

CAR T cells

T cells taken from the blood and given an engineered receptor (a chimeric antigen receptor, CAR) so that they recognise and kill cells carrying a chosen surface protein. Used as a treatment for some blood cancers; a demanding therapy with serious possible side effects.

Also: CAR-T cells, CAR T cell, CAR-T cell

Cohort

A group of people that researchers follow over time, often for years, recording their health and habits. A cohort study is observational: it can show that two things go together, not that one causes the other.

Also: cohort study

D

Dementia

A loss of memory, thinking and everyday abilities that is severe enough to interfere with daily life. Alzheimer's disease is the most common cause; vascular disease of the brain is another.

DNA methylation

Small chemical tags (methyl groups) attached to DNA. They don't change the genetic code but help decide which genes are switched on. The pattern of these tags shifts with age in a predictable way, which is what epigenetic clocks read.

Also: methylation

E

Epigenetic clock

A formula that estimates age from the pattern of DNA methylation in a sample, usually blood. Early clocks were trained to predict age in years; newer ones, such as GrimAge or DunedinPACE, were trained to predict disease, death or the pace of aging.

Also: methylation clock

F

Fibroblasts

The cells that build connective tissue, the framework that holds organs and skin together. They are easy to grow in the lab, so many aging experiments use fibroblasts taken from skin.

Also: fibroblast

Frailty

A state, common in old age, in which the body has little reserve: weakness, slow walking, tiredness, weight loss and low activity. Frail people recover less well from illness, falls or surgery.

H

Healthspan

The part of life spent in good health, without serious disease or disability. Many aging researchers care more about lengthening healthspan than lifespan.

Hippocampus

A seahorse-shaped part of the brain, one on each side, that is essential for forming new memories. It shrinks with age and is among the first areas damaged in Alzheimer's disease.

Hormone therapy

Prescription estrogen, often combined with a progestin, used to relieve menopause symptoms. It has benefits and risks that depend on the person, the type of hormone and the timing, and it is decided together with a doctor.

Also: menopausal hormone therapy, hormone replacement therapy

I

Inflammation

The immune system's response to injury or infection: blood flow, immune cells and signalling molecules rush to the site. Useful in short bursts, it does harm when it smoulders for years. The low-grade, long-lasting inflammation that comes with age is sometimes called “inflammaging”.

Also: inflammaging, chronic inflammation

Insulin

A hormone made by the pancreas that tells cells to take up sugar from the blood. When cells respond poorly to it (insulin resistance), blood sugar rises, a step towards type 2 diabetes.

L

Lifespan

How long an organism lives. In animal studies, “median lifespan” is the age by which half the animals have died, and “maximum lifespan” is usually the age reached by the longest-lived tenth.

Lysosome

A small sac inside the cell filled with digestive enzymes: the cell's recycling centre, where material delivered by autophagy is broken down.

Also: lysosomal

M

Macrophages

Large immune cells that swallow germs, dead cells and debris, and send out signals that start or calm inflammation. Almost every tissue has its own resident macrophages.

Also: macrophage

Mendelian randomization

A way to test cause and effect with genetic data. Because genes are handed out at random at conception, people who inherit variants linked to, say, higher cholesterol act like a natural experiment. The method rests on assumptions that can't always be checked.

Metformin

A cheap, widely used prescription drug for type 2 diabetes. It is being studied as a possible way to slow aging, but that use is unproven. It can cause stomach upset and is not suitable for everyone.

Microbiome

The trillions of bacteria and other microbes living in and on the body, most of them in the gut. They help digest food and make substances, such as short-chain fatty acids, that affect the rest of the body.

Also: microbiota, gut bacteria, gut microbes

Mitochondria

The power plants of the cell: small structures that burn sugar and fat with oxygen to make ATP, the cell's energy currency. They have their own small piece of DNA and tend to work less well with age.

Also: mitochondrion, mitochondrial

mTOR

A protein that senses nutrients and growth signals. When food is plentiful, mTOR tells cells to grow and build; when it is switched down, cells shift to repair and autophagy. The drug rapamycin blocks it.

N

NAD+

A molecule every cell needs to turn food into energy and to run some repair enzymes. Its levels fall with age in many tissues, which has made it a popular target for research and for supplements whose benefits in people are unproven.

Also: NAD

O

Observational study

A study that watches what people do and what happens to them, without assigning a treatment. It can show links (associations) but not causes, because people who differ in one habit often differ in many others.

Also: observational

P

Peer review

The check a paper goes through before a journal publishes it: other scientists read it, point out problems and recommend changes. It catches many errors but not all.

Also: peer-reviewed, peer reviewed

Placebo

A dummy treatment, such as a sugar pill or a salt-water injection, that looks like the real one. Comparing against a placebo shows how much of an effect comes from the treatment itself rather than from expectation or chance.

Polygenic score

A single number that adds up the small effects of many thousands of common gene variants a person carries, to estimate their inherited tendency toward a trait or disease. It describes a tendency, not a certainty: most people with a high score never get the disease.

Also: polygenic risk score, polygenic risk scores

Preprint

A paper shared publicly before peer review, on servers such as bioRxiv and medRxiv. Preprints spread results quickly, but the findings may change or not hold up.

Proteomics

Measuring thousands of proteins at once, for example in a blood sample. The full set of proteins is called the proteome; patterns in it can be used to build aging clocks.

Also: proteome

R

Randomized controlled trial

An experiment in which participants are assigned by chance to the treatment or to a comparison group (often a placebo). Because chance, not choice, decides who gets what, the groups are alike in every other way, so differences in outcome can be put down to the treatment.

Also: randomized trial, randomised trial, randomized

S

Sarcopenia

The loss of muscle mass, strength and function with age. When it is severe, it makes falls, frailty and loss of independence more likely.

SASP

The mix of signalling molecules, enzymes and growth factors that senescent cells release. It can spread inflammation and push neighbouring cells towards senescence.

Also: senescence-associated secretory phenotype

Senescent cells

Cells that have permanently stopped dividing but don't die. They pile up with age and release a mix of inflammatory signals (the SASP) that can harm the tissue around them. They are sometimes called “zombie cells”.

Also: senescent cell, senescent, cellular senescence, senescence

Senolytics

Drugs that kill senescent cells while sparing healthy ones. The best known are the leukaemia drug dasatinib combined with quercetin, a plant compound, and fisetin. All are still experimental for aging.

Also: senolytic

Short-chain fatty acids

Small molecules such as acetate, propionate and butyrate that gut bacteria make when they ferment fibre. They feed the cells lining the gut and act as signals elsewhere in the body.

Also: short-chain fatty acid

Statistically significant

A result is called statistically significant when it would be unlikely to show up by chance alone if there were no real effect. It says nothing about how large or important the effect is.

Also: statistical significance

Stem cells

Cells that can divide to renew themselves and also turn into specialised cells, such as muscle or blood cells. Tissues rely on them for repair; their numbers and activity tend to decline with age.

Also: stem cell

T

T cells

White blood cells that recognise and kill infected or abnormal cells, or direct the rest of the immune response. They mature in the thymus.

Also: T cell, T-cell, T-cells

Target trial emulation

A way of analysing existing records or survey data as if they came from a randomized trial: the researchers first write down the rules of the trial they would like to run (who is eligible, which treatments are compared, when follow-up starts) and then apply them to the data. It avoids some common errors of observational studies, but because no one was assigned a treatment at random, hidden differences between the groups can still explain the results.

Also: target trial

V

VO₂max

The most oxygen the body can use during all-out exercise, a standard measure of aerobic fitness. It declines with age and is strongly linked to health in later life.

Also: VO2max