The 12 hallmarks of aging
What actually happens inside your cells as you age, and which of it you can influence.
In 2013, a group of researchers led by Carlos López-Otín published a paper that gave the field a shared map: nine "hallmarks" of ageing, the biological processes that drive decline. In 2023 they updated it to twelve. It's one of the most cited papers in biology, and it's the best short answer to the question "why do we age?"
You don't need to memorise it. But the map explains why the same few habits keep appearing in every chapter of this course: they touch several hallmarks at once.
The three groups
The hallmarks fall into three layers.
Primary hallmarks are the causes of damage.
Antagonistic hallmarks are the body's responses to that damage: helpful in small doses, harmful when they run out of control.
Integrative hallmarks are what happens when damage and responses pile up: tissues lose their ability to repair themselves and to communicate.
The twelve, in plain English
| Hallmark | What it means | What nudges it |
|---|---|---|
| Genomic instability | DNA damage builds up faster than it's repaired | Not smoking, sun protection, less alcohol |
| Telomere attrition | The protective caps on chromosomes shorten | Linked with exercise, sleep and lower stress |
| Epigenetic alterations | Genes switch on and off in the wrong places | Measured by epigenetic clocks; responds to lifestyle |
| Loss of proteostasis | Proteins misfold and clump together | Exercise; sleep, when the brain clears waste |
| Disabled macroautophagy | Cells stop recycling their own junk | Exercise, periods without food |
| Deregulated nutrient sensing | Insulin and growth pathways stay switched on | Healthy waist, muscle, not overeating |
| Mitochondrial dysfunction | The cell's power plants lose efficiency | Aerobic training, especially zone 2 and intervals |
| Cellular senescence | "Zombie" cells stop dividing but won't die, and leak inflammation | Exercise; drug research is ongoing |
| Stem cell exhaustion | The body's repair cells run low | Strength and aerobic training |
| Altered intercellular communication | Tissues signal badly to each other | Most of the above, plus sleep |
| Chronic inflammation | Low-grade inflammation that never switches off, or "inflammaging" | Waist size, sleep, movement, food, oral health |
| Dysbiosis | The gut microbiome loses diversity | Fibre, plant variety, fermented foods |
Why this matters for you
The hallmarks are connected. Damage in one accelerates others. Chronic inflammation, for example, both results from and worsens several of them. That's why ageing can feel like it speeds up, and why broad habits beat narrow fixes.
The strongest levers are unglamorous. Exercise shows up in almost every row of that table. So do sleep, a healthy waist and not smoking. No supplement or device comes close to that breadth.
Be sceptical of single-hallmark promises. Many products claim to "reverse" one hallmark. Most of the evidence behind them comes from cells or mice. That research is genuinely exciting, but "works in a mouse" and "adds healthy years to a human" are very far apart. The Advanced protocols chapter covers how to judge these claims.
Key idea
Every foundation habit in this course acts on several hallmarks at once. That's why the boring habits win.
This week
- Pick the hallmark that surprised you most and read one article about it.
- Look at the "What nudges it" column and count how many rows mention exercise. That's your answer to what to prioritise.
- If you smoke or vape, stopping is the single highest-impact change on this entire page.
In the journal
The hallmarks are why the journal's evening page starts with the same three non-negotiables every day: sleep, exercise and nutrition. Small, daily and broad beats rare and targeted.
Sources: López-Otín et al., "Hallmarks of aging: an expanding universe", Cell 2023 · López-Otín et al., "The hallmarks of aging", Cell 2013