Research terms, explained.

AMPK (AMP-activated protein kinase) is a cell energy sensor that switches on energy production and slows energy-using processes when cell energy runs low.

An animal study tests a treatment in living animals, usually mice or rats, to see effects that cell cultures cannot show.

Bioavailability is the share of a substance that reaches the bloodstream, or its target tissue, in an active form.

Cellular senescence is a state in which a cell stops dividing but stays alive, and it releases inflammatory signals that can harm nearby tissue.

A confidence interval is a range that is likely to contain the true size of an effect, given the data and the size of the study.

A crossover trial gives each participant both the treatment and the control, in random order, with a break between the two periods.

Double-blind means that neither the participants nor the researchers who assess the outcomes know who received the active treatment.

Effect size measures how large a difference is, not just whether one exists.

The epidermis is the outer layer of skin, and the dermis is the thicker layer beneath it, which holds collagen, elastin and blood vessels.

An in vitro study is an experiment in cells or tissues grown outside the body, such as in a culture dish.

Industry funding is money from a company that makes the product being studied. It can shape study design, reporting and results.

A meta-analysis combines the numerical results of several studies into one pooled estimate.

Mitochondria are structures inside cells that produce most of the cell’s energy, as ATP, using oxygen.

NAD+ (nicotinamide adenine dinucleotide) is a coenzyme in every cell that carries electrons in energy production and is used by enzymes that repair DNA.

An observational study records what people do or have and looks for links between them, without assigning a treatment.

Oxidative stress is an imbalance in which reactive oxygen molecules outnumber a cell’s defences, causing damage to proteins, fats and DNA.

A p-value is the probability of seeing a result at least as large as the one observed if there were really no effect.

Photobiomodulation (PBM) is the use of low-power red or near-infrared light to change how cells behave. Research mainly points to the mitochondrial enzyme cytochrome c oxidase.

A placebo is an inactive treatment, such as a sugar pill or a cream without the active ingredient, given to a control group so that the expected effect of taking part can be separated from the real effect.

A preprint is a scientific paper posted online before it has been checked by peer review.

A randomized controlled trial (RCT) assigns people by chance to a treatment group or a comparison group. It is the strongest design for testing whether something causes an effect.

A sham control is a fake procedure, such as a device that is switched off or a mock treatment, used when a placebo pill is not possible.

A surrogate endpoint is a measurable marker, such as a blood level or a telomere length, used in place of an outcome people care about, such as disease or survival.

A systematic review gathers all the studies on a question using a pre-set search and inclusion rules, then summarizes what they show.

Telomeres are protective caps of repeated DNA at the ends of chromosomes, and they shorten each time a cell divides.