What causes aging: the hallmarks of aging, telomeres and senescent cells, what inflammaging is, why we die of old age, whether aging can be reversed (the old mice), why some people age faster than others, what biological age is, and why evolution didn't get rid of aging.
The full answer
Why do we age?
Why do we age? We age because damage builds up in our cells faster than the body can clear it, and the inflammation that's meant to heal us stops fully switching off, which scientists call inflammaging. I'm Justin Hartfield, I've spent twenty-five years in cannabis, and in mice, the system cannabis works on is part of that cleanup.
What causes aging?
What causes aging? In 2013, scientists led by Carlos López-Otín in Spain listed nine hallmarks of aging, from damaged DNA and worn-down telomeres to cells that stop dividing. In 2023 they made it twelve, with chronic inflammation among them.
Telomeres and senescent cells
Telomeres are the caps on the ends of your chromosomes, and in 1990 Calvin Harley's team showed they get shorter each time human cells divide in a dish. That may be part of why a cell eventually stops dividing for good.
Cells that stop dividing are called senescent cells, and they sit in your tissues leaking inflammatory signals. In 2016, a team at the Mayo Clinic cleared them out of normally aging mice from their first birthday on. Those mice lived about a quarter longer, with healthier hearts and kidneys.
What is inflammaging?
What is inflammaging? Think of the fight your body starts when you scrape your knee, and imagine it never quite ending.
Researchers call it inflammaging. As we get older, the fight switch never fully turns off.
The Italian immunologist Claudio Franceschi named it in 2000, and he argued that inflammation protects you while you're young and turns harmful late in life, in years evolution never planned for.
The biologist Dr. Bob Melamede, who I met in 2010 and who died in 2023, had his own framework for why this happens.
Dr. Bob thought aging was mostly a cleanup crew falling behind, and that the body's own keys, along with the plant's, could help it catch up. Parts of that have good evidence in mice. In people, it's still a theory.
Free radicals are the friction of life, and endocannabinoids are the oil of life.
Why do we die of old age?
Why do we die of old age? We die of the illnesses it brings, because age is the biggest risk factor for most of them.
A century ago, most people died of infections. Today most die of heart disease, cancer and other illnesses of age and inflammation.
Can aging be reversed?
Can aging be reversed? In mice, some of its effects have been turned back, including a drop in learning tied to the endocannabinoid system. In older animals, that system's main lock in the brain, CB1, works less well.
Mice born without CB1 age early. In old mice, a tiny daily dose of THC brought their learning back to the level of young ones. In young mice, it made it worse.
That was a team at the University of Bonn in 2017, working in mice, so what it means for people is still open.
Why do some people age faster than others?
Why do some people age faster than others? Less of it is in your genes than you'd think. In 1996, a study of almost three thousand pairs of Danish twins put the genetic share of lifespan at about a quarter. In 2018, family trees covering hundreds of millions of people put it below ten percent.
What is biological age?
What is biological age? It's how old your body acts, which can differ from the number of birthdays you've had. In 2013 the scientist Steve Horvath built a clock from chemical marks on DNA, and it can read a tissue as older or younger than its years.
Why didn't evolution get rid of aging?
Why didn't evolution get rid of aging? In 1977, the biologist Tom Kirkwood argued that bodies save energy by skimping on the repair of their own cells, so small errors pile up over a lifetime. To me, that's the cleanup crew falling behind, seen from evolution's side.
So we age because damage slowly outpaces repair, and the fight that heals you never quite switches off. The whole film is on my site, linked below, and next, how your body heals itself.
What the studies show
Every claim in this answer, the study behind it, who was studied, and who paid for the research. “None listed” means the paper names no funder.
