NAD⁺ metabolism, sirtuin activation, epigenetic clocks, mTOR signaling, and cellular senescence — the science of why we age and what the evidence actually says about slowing it down.
Epigenetic Age vs. Chronological Age
Genetics account for roughly 25% of longevity variance. The rest — lifestyle, environment, and targeted interventions — is within your control.
The Science
First described by López-Otín et al. (2013), updated to 12 hallmarks in 2023. Each represents a mechanism of biological aging that is theoretically targetable.
Accumulated DNA damage from oxidative stress, radiation, and replication errors. The primary driver of cancer risk with age.
Telomere shortening with each cell division limits replicative capacity and triggers senescence. Measurable via telomere length assays.
Changes in methylation patterns, histone modifications, and chromatin remodeling. The basis of epigenetic clocks (GrimAge, DunedinPACE).
Failure of protein quality control — misfolded proteins accumulate. Directly implicated in Alzheimer's, Parkinson's, and metabolic disease.
Declining autophagic flux reduces cellular "housekeeping." Fasting, rapamycin, and exercise are the most evidence-backed activators.
Dysregulation of mTOR, AMPK, IGF-1, and sirtuins with age. The mechanistic target of caloric restriction and intermittent fasting benefits.
Declining mitochondrial number and efficiency with age. NAD⁺ is directly upstream of sirtuin-mediated mitochondrial biogenesis.
Accumulation of non-dividing but metabolically active cells secreting pro-inflammatory SASP factors. Target of emerging senolytic drugs.
NAD⁺ decline is one of the most well-documented features of biological aging. Sirtuin pathways — SIRT1, SIRT3, and especially SIRT6 — depend on it. But the jump from rodent studies to human clinical benefit is messier than the supplement industry suggests.
Both nicotinamide mononucleotide and nicotinamide riboside raise NAD⁺ levels — but by different pathways, at different rates, with different tissue distributions. Here's what the human trials show.
SIRT6 overexpression extends lifespan in mice by 15–30%. It regulates IGF-1 signaling, NF-κB inflammatory cascades, and telomeric integrity. The most clinically compelling sirtuin target we have.
Whole blood NAD⁺ measurement is widely available but reflects a different pool than intracellular (PBMC) testing. Understanding the distinction matters before spending money on supplementation.
Horvath's original clock measured methylation age. DunedinPACE measures the pace of aging in real time. GrimAge predicts lifespan and healthspan outcomes. A clinical breakdown of what each captures — and doesn't.
Exercise, dietary restriction, metformin, and rapamycin all show epigenetic age deceleration in studies. The Horvath TRIIM trial reversed biological age 2.5 years in one year. What's actionable today?
PhenoAge estimates your current biological age from clinical labs. DunedinPACE measures how fast you're aging right now. One is a snapshot; the other is a speedometer. Both matter clinically.
Senescent cells don't die — they linger and secrete a pro-inflammatory cocktail called the SASP. They're implicated in atherosclerosis, neurodegeneration, and sarcopenia. Fisetin and dasatinib/quercetin are the leading senolytic candidates.
The Mayo Clinic's dasatinib + quercetin trials showed selective clearance of senescent cells in humans. Fisetin has strong rodent data. What does the human trial evidence actually support — and what's still preclinical?
mTOR inhibition is the most replicated longevity intervention across species. Intermittent fasting, caloric restriction, and rapamycin all converge on this pathway. The clinical translation is more nuanced than most summaries suggest.
Autophagy clears damaged organelles and misfolded proteins — and it declines dramatically with age. Exercise, fasting, and spermidine are the most validated inducers. What the timing and threshold data actually shows.
The TAME trial is the first FDA-approved longevity trial using a pharmaceutical endpoint. Metformin inhibits complex I of the electron transport chain and activates AMPK. Summarizing where the evidence stands in 2025.
Every 1 MET increase in VO₂ max confers roughly 13% reduction in all-cause mortality. The Peter Attia framework puts Elite fitness as the single most powerful longevity intervention available without a prescription.
Zone 2 cardio — exercising at ~60–70% max heart rate — is the primary driver of mitochondrial biogenesis and metabolic flexibility. Why it matters for longevity beyond just cardiovascular fitness.
Resveratrol activates SIRT1 and AMPK in vitro. Human bioavailability is poor with standard oral dosing. Pterostilbene has better pharmacokinetics. An honest review of where polyphenol research stands in 2025.
Spermidine induces autophagy, reduces cardiovascular risk, and is associated with lower all-cause mortality in epidemiological data. The PROBIOM and SMARTage trials give it a credibility most longevity supplements lack.
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