Here's A Longevity Science Glossary: Healthspan, Senolytics and More

A plain-language longevity science glossary: healthspan, hallmarks of aging, senolytics, epigenetic clocks, NAD+ precursors and peptide bioregulators.

Longevity science has acquired its own language, and that language has escaped the laboratory. Words that were coined in review papers a decade ago now appear on podcasts, clinic websites and product labels, often with their original meaning worn smooth. This glossary defines the terms a reader meets most often. It explains what each word means and where it came from. It does not rank interventions or say that any of them works; a definition is not an endorsement.

Lifespan is how long an organism lives. Life expectancy is a population average; maximum lifespan is the longest any member of a species has been recorded to live. The two are routinely confused in headlines. Healthspan is the portion of life spent in good health, free of serious chronic disease and disability. It has no single agreed measurement, which is worth remembering whenever a study claims to have extended it.

Geroscience is the field that studies biological aging as the shared root of many chronic diseases. Its working assumption, the geroscience hypothesis, is that addressing the biology of aging itself could delay several age-related diseases together rather than one at a time. It is a research agenda, not an established result. Chronological age is the number of years since birth. Biological age is an estimate of how far along the aging process a body is, inferred from biomarkers. The first is a fact; the second is always a model's output.

Hallmarks of aging refers to a framework published in the journal Cell in 2013, which grouped the biology of aging into nine categories, including genomic instability, telomere attrition, epigenetic alterations and cellular senescence. A 2023 update expanded the list to twelve, adding chronic inflammation, disabled macroautophagy and dysbiosis. The hallmarks are an organizing scheme for research, not a checklist of targets with proven remedies.

Cellular senescence is a state in which a cell permanently stops dividing but does not die. Senescent cells release a mixture of signaling molecules known as the SASP, senescence-associated secretory phenotype. Autophagy, literally "self-eating," is the cell's process for breaking down and recycling its own components. Epigenetics covers chemical marks on DNA and its packaging proteins that influence which genes are active without changing the DNA sequence itself. DNA methylation is the most studied of these marks.

A biomarker is any measurable indicator of a biological state. A biomarker of aging is useful only insofar as it predicts real outcomes, and establishing that takes time. Epigenetic clocks are statistical models that estimate age from DNA methylation patterns. Steve Horvath published the first widely used multi-tissue clock in 2013. Later clocks were trained to predict mortality risk or the pace of aging rather than calendar age. Different clocks can give the same person different answers, because they were built to measure different things.

Geroprotector and gerotherapeutic are umbrella terms for any compound or intervention proposed to act on the aging process. The words describe an intention. They do not certify a result. Senolytics are compounds studied for their ability to eliminate senescent cells selectively; the term dates from 2015. Senomorphics are compounds studied for altering what senescent cells secrete without removing them. NAD+ is a coenzyme present in every cell and involved in energy metabolism. NAD+ precursors, chiefly nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN), are molecules the body can convert into it.

Peptide means a short chain of amino acids, and in longevity circles the single word covers very different things: approved prescription drugs, injectable compounds sold as "research peptides," and oral products. Among the oral products are peptide bioregulators, a supplement category named in the research tradition of the Russian gerontologist Vladimir Khavinson.

The term refers either to a natural peptide complex extracted from a single animal tissue or to a synthesized chain of two to four amino acids, and products are labeled accordingly, by tissue source or by trade name. As with every entry in this section, the phrase tells you how a product is classified and named. It makes no statement about what the product does.

Peptide bioregulator deserves a line of its own, because the phrase is older than most of this vocabulary. It goes back to work begun in Leningrad in the 1970s, where the first tissue extracts were named Thymalin and Epithalamin. The best-known synthesized sequence from the same school is the four-amino-acid chain Ala-Glu-Asp-Gly, known as Epitalon. Khavinson peptides is an informal synonym for the whole category. Both expressions name a research school and a way of classifying products, not a demonstrated result.

A few further terms do more to protect a reader than any of the above. In vitro means in cells or tissue outside a living organism. In vivo means in a living organism, which in aging research most often means worms, flies, or mice. Preclinical covers both.

When a new longevity claim arrives, find its nouns in the lists above and then ask three questions. Was this shown in cells, animals or people? Was the thing measured a surrogate or an outcome? Has anyone outside the original group repeated it? The vocabulary of longevity is rich and still growing, and most of it is sound science described carefully. Knowing exactly what each word does and does not assert is what lets a reader tell the careful descriptions from the rest.