mTOR Signaling

mTOR is a serine/threonine kinase that forms two complexes, mTORC1 and mTORC2. mTORC1 responds to amino acids, glucose, and growth factors and drives protein synthesis, ribosome biogenesis, and lipid synthesis while suppressing autophagy [1]. When nutrients are abundant, mTORC1 activity is high; cells grow and divide. When nutrients are scarce, mTORC1 activity falls and autophagy switches on.

Genetic or pharmacological inhibition of mTOR extends lifespan in yeast, worms, flies, and mice. The National Institute on Aging's Interventions Testing Program found that rapamycin, an mTOR inhibitor, extended median lifespan in genetically heterogeneous mice by roughly 9-14% in males and up to 18% in females depending on dose and start age, one of the largest and most reproducible pharmacological lifespan effects in mammals [2]. In humans, no RCT has tested rapamycin for lifespan extension; the closest human data are trials in older adults using low-dose rapamycin analogs (rapalogs) for immune function, where a 2014 trial found improved influenza vaccine response in adults over 65 taking RAD001 for six weeks, evidence of an anti-aging immune effect rather than mortality benefit [3]. A separate review of mTOR as a central regulator of lifespan across species noted that the immune-boosting rapalog effect and the lifespan-extending mouse effect likely involve overlapping but not identical downstream pathways [5].

What the evidence does not show: no long-term human safety or efficacy data exist at anti-aging doses, and mTOR inhibition carries real costs, including impaired wound healing, mouth ulcers (stomatitis), elevated blood glucose, and immunosuppression at higher doses used in transplant medicine [1]. Whether intermittent, low-dose "weekend" rapamycin dosing used by longevity clinics achieves benefit without these costs is unproven in controlled trials.

Bryan Johnson took rapamycin as part of his Blueprint protocol for nearly five years before stopping on September 28, 2024. He wrote on the Blueprint blog that despite testing multiple dose schedules (5-13 mg weekly to biweekly), he saw intermittent skin and soft-tissue infections, lipid abnormalities, glucose elevations, and increased resting heart rate, and that a preprint reporting accelerated epigenetic aging across 16 clocks in some rapamycin users factored into his decision; he framed this explicitly as an n=1 self-report, not a controlled trial result [4].

Critics including gerontologist Matt Kaeberlein, who ran mouse rapamycin studies himself, caution that mouse dose-response data do not map directly onto safe human anti-aging doses, and that rapamycin's growth-suppressing and immune effects make the risk-benefit calculation genuinely uncertain outside of short courses [2]. The original mouse lifespan-extension finding has since been replicated at multiple independent test sites and start ages under the National Institute on Aging's Interventions Testing Program protocol, one reason it is regarded as among the more reproducible results in the field [6]. Separately, the human-relevant TAME metformin trial, which shares conceptual ground with mTOR-pathway aging research since metformin also modulates nutrient-sensing signaling, remains only partially funded as of recent reporting, illustrating the practical difficulty of running large aging-outcome trials in humans regardless of mechanism [7].

The plain takeaway: mTOR inhibition is the most consistently lifespan-extending manipulation across species, but the human dose that captures benefit without meaningful side effects has not been established.