Reversing Your Real Biological Age

Dive into the fascinating world of longevity with Dr. Hillary Lin as she explores the biology of aging and how to slow it down. Discover the secrets of bi…

Published September 20, 2024The Longevity Show

Two people who are both 50 can be decades apart biologically, and Dr. Lin's argument is that this gap is unusually malleable — more so than most of what medicine measures. Her analogy is two cars of the same model year, one gently driven and maintained, the other run hard through snow and neglected. But she extends it in a way most people skip: a car left in a garage also breaks down. You cannot protect yourself by doing nothing, because disuse is its own form of decay, which is the argument for hormesis rather than avoidance.

The organising idea is that aging runs through three identifiable mechanisms — senescent cells that stop dividing but refuse to die while leaking inflammatory signals, telomeres shortening each time a cell divides, and mitochondria producing more pollution than energy. Biological clocks like the Horvath clock attempt to measure the resulting wear through DNA methylation patterns. Dr. Lin's caveat on those clocks is the most useful thing in the section: none are accurate enough to take literally, with roughly 7% variation even on common epigenetic tests, so they are ballpark instruments rather than precision ones.

The interventions are geroprotectors and senolytics, and she is notably uneven about them in a way that reads as honest. Rapamycin she both prescribes and takes herself, disclosing this upfront. Metformin she considers theoretically compelling, very safe, and not something she puts everyone on — because unlike rapamycin it has not replicated the lifespan extension in animal work. Polyphenols get the most enthusiasm partly because they are food. And she is careful to remove blame from the equation: a great deal of biological aging comes from environmental exposures, sedentary work and pollution that no individual chose.

Before you watch

The three mechanisms are worth being able to name. Cellular senescence produces zombie cells that stop dividing but will not die, taking up space and releasing inflammatory signals that damage healthy neighbours. Telomere shortening wears down the protective ends of DNA with each division — Dr. Lin's image is book covers fraying as the book is pulled off the shelf repeatedly. And mitochondrial dysfunction turns the cell's power plants into sources of pollution rather than energy.
Longer telomeres are better on average and catastrophic in the individual case, which is a nuance most coverage omits. A cell with effectively unlimited telomeres becomes immortal and replicates forever — and cells that replicate forever are cancer cells. So the target is a longer average across the body, not infinite length in any particular cell line. Dr. Lin also notes that individual cell death is not a problem to be solved: your body recycles the parts of cells that have undergone orderly apoptosis into new ones.
Biological clocks deserve to be read as ballpark rather than precise, and the error bars matter. Dr. Lin cites roughly 7% variation even in the most common epigenetic tests, which she points out is practically 10% — an enormous swing when applied to a person's biological age. Her guidance is to use them directionally: if you are 30 and the test says 50, that gap is meaningful; if you retest and the number moves modestly, that is noise. Phenotypic age can be calculated free from routine lab values, while telomere length requires a commercial provider.
Her framing on blame is deliberate and worth preserving. A great deal of what drives biological aging sits outside individual control — additives in processed food, sedentary work, environmental pollution — and she raises this specifically because patients arrive believing their biological age is a personal failing. Her related aside is about social environment: one of the oldest centenarians said her secret was avoiding toxic people, and Dr. Lin extends this to what she calls emotional vampires, noting that some are entirely well-meaning and that over-nurturing is its own unhealthy dynamic requiring boundaries.
On rapamycin she discloses that she both prescribes it and takes it herself, and is emphatic it is not a DIY project. It inhibits mTOR — the mammalian target of rapamycin, named after the drug rather than the other way round — which regulates growth and aging. mTOR activity is what you want when young and growing; sustained high activity later accelerates aging. Her analogy is driving at full speed permanently: useful for getting started, destructive as a steady state.
The dosing logic explains why rapamycin is taken weekly rather than daily. The point is intermittency — giving the body a pause to shift from constant growth into repair — and a week is common partly because it is easy to remember and because the drug has cleared by then. Clearance varies substantially between people and can be measured by blood test. Dr. Lin's illustration of individual variation is caffeine: her partner can drink coffee an hour before sleeping while she needs twelve hours, being a slow metaboliser. Pharmacogenomic testing exists, though she notes clinical practice often finds the answer faster by trial and observation.
The rapamycin evidence spans strong animal data and narrower human findings. It extends lifespan in mice; in humans it has been shown to improve immune function in older adults and reduce markers of aging in skin. The result she is most excited about is the VIBRANT pilot study at Columbia on preserving ovarian reserve in women with premature ovarian insufficiency, using AMH as the readout precisely because it shifts enough month to month to show a difference at three or six months. Her accompanying caution is carefully built rather than dismissive: the studies on offspring outcomes have not been done, and her reason for cautious optimism is that transplant patients take far higher daily doses — high enough to be genuinely immunosuppressive, which intermittent longevity dosing is not — and have gone on to have healthy children. She is explicit that this is reassuring context rather than evidence.
Metformin gets the most honest assessment in the episode. It activates AMPK, improving glucose metabolism and inducing autophagy, and observational data associates it with lower risks of cardiovascular disease, cancer and neurodegeneration — with the TAME trial investigating whether it could be formally classified as an anti-aging drug. But Dr. Lin does not put everyone on it, because unlike rapamycin it has not reproduced lifespan extension in animal studies. Her verdict: if the choice is between metformin and exercising more, exercise. She also flags that long-term metformin impairs absorption of B vitamins, particularly B12, which should be screened — the same applying to long-term proton pump inhibitors like omeprazole.
Polyphenols work through two mechanisms, not one. The familiar one is antioxidant — Dr. Lin's image is a squad of firefighters putting out small fires of oxidative stress and inflammation before they damage cells, DNA and mitochondria. The less familiar one is epigenetic: polyphenols interact with cell signalling pathways, switching on genes that promote longevity and switching off those driving inflammation and cell death. They activate the same pathways triggered by caloric restriction, which matters because sustained caloric restriction at 800-1,000 calories a day is not realistic for humans and its advantage reverses the moment you stop.
Her polyphenol list comes with sources and one honest retraction. Hydroxytyrosol in extra virgin olive oil, which she uses for nearly everything. Quercetin in onions, apples, berries and almonds — which doubles as a senolytic. EGCG in green tea, ideally organic since thin tea leaves absorb pesticides readily. Curcumin in turmeric, paired with black pepper to improve absorption. Luteolin in peppers, carrots and celery, which boosts Nrf2. And flavonoids including catechin and epicatechin in dark chocolate at 70% cacao or higher. On resveratrol she is candid that it was studied in yeast and did not hold up in human follow-up — disclosing that sirtuins were the subject of her first research lab in high school.
The senolytic evidence has moved into human trials for one specific disease. Dasatinib, an anti-cancer drug, combined with quercetin has reduced senescent cell burden and improved tissue health in animal models — and in small human trials for idiopathic pulmonary fibrosis, treated patients showed improvements in lung function. Dr. Lin notes a friend's parent has IPF, a condition with no good treatments that leads to lung transplantation and early death. Fisetin, found in strawberries, apples and cucumbers, has shown senolytic properties in animal studies. The larger bet underlying the field is that treating aging itself may reverse decline in diseases that have no effective treatment of their own.

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Questions

How accurate are biological age tests?

Less accurate than the confident number they return suggests. Dr. Lin cites roughly 7% variation even in the most common epigenetic tests — which she points out is practically 10%, an enormous swing when translated into years of biological age. Her guidance is to read them as ballpark instruments: if you are chronologically 30 and the result says 50, the direction is meaningful and worth acting on; if you retest and the number shifts modestly, that is measurement noise rather than progress or decline. She suggests comparing multiple approaches rather than trusting one, noting phenotypic age can be calculated free from routine lab values while telomere length requires a commercial provider.

What actually makes you age biologically?

Dr. Lin focuses on three mechanisms. Cellular senescence produces so-called zombie cells that have stopped dividing but refuse to die, occupying space while releasing inflammatory signals that damage nearby healthy cells and drive conditions like cancer and heart disease. Telomere shortening wears away the protective ends of your DNA each time a cell divides, eventually pushing cells into senescence or death. And mitochondrial dysfunction means the cell's power plants produce more harmful byproducts than usable energy. Underlying all three is entropy — she notes the body inevitably misses things while maintaining itself, which is why upkeep has to be continuous rather than one-time.

Are longer telomeres always better?

On average yes, in any individual cell absolutely not — and this is the nuance most discussion misses. People with longer average telomeres do tend to live longer, so the population-level signal is real. But a cell with effectively unlimited telomeres becomes immortal and keeps replicating indefinitely, and cells that replicate forever are cancer cells. So what you want is a longer average across the body, not maximal length anywhere in particular. Dr. Lin adds a related correction: individual cell death is not a failure to be prevented, since your body recycles the components of cells that have died in the orderly, programmed way into new ones.

Should I take rapamycin for longevity?

Dr. Lin both prescribes it and takes it herself, and discloses that upfront — while being emphatic that this is off-label use and not something to source or self-administer. It works by inhibiting mTOR, the pathway regulating growth versus repair, and the dosing is deliberately intermittent, most commonly weekly, so the body gets periods of repair rather than continuous growth signalling. The evidence includes lifespan extension in mice, improved immune function in older adults, reduced markers of skin aging, and a pilot study at Columbia on preserving ovarian reserve in premature ovarian insufficiency. Her instruction is to do this alongside a longevity physician who understands both the drug and your goals.

Is metformin worth taking if I'm not diabetic?

Dr. Lin's answer is more sceptical than the longevity field's general enthusiasm. Metformin activates AMPK, improving glucose metabolism and inducing autophagy, and observational data links it to lower rates of cardiovascular disease, cancer and neurodegeneration — with the TAME trial examining whether it should be formally classified as an anti-aging drug. But she does not put everyone on it, because unlike rapamycin it has not reproduced lifespan extension in animal studies despite being theoretically compelling and extremely safe across millions of users. Her framing is a direct comparison: if the choice is between starting metformin and exercising more, exercise. She also notes long-term use impairs B12 absorption, so B vitamins should be screened.

What are senolytics and is there human evidence yet?

Senolytics selectively target and eliminate senescent cells — the ones that have stopped dividing, skipped programmed cell death, and now sit in tissue releasing inflammatory signals that harm their neighbours. Dr. Lin's analogy is a broken-down car blocking a busy highway, polluting and causing damage around it. The best-known combination is dasatinib, an anti-cancer drug, with quercetin, the polyphenol found in apples and onions. Beyond animal models, it has been used in small human trials for idiopathic pulmonary fibrosis — a condition with no good treatments that progresses to lung transplantation — where treated patients showed improvements in lung function. Fisetin, found in strawberries, apples and cucumbers, has shown senolytic properties in animal studies.

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