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Half of it may be written.
The other half is still yours.
Twin research has suggested that genetics may account for a larger share of lifespan variation than scientists once assumed. What that finding also reveals — quietly, in the other direction — is that roughly half of the story may still be shaped by the choices, inputs, and biology a life accumulates over time.
I
What twin research has suggested about
genetics and how long we may live.
For decades, the dominant view in longevity science was reassuring in a specific way: genes, researchers generally concluded, account for perhaps a quarter of the variation in how long people live. The rest — the majority — was attributed to environment, behavior, and the accumulated biology of how a life is lived. The implication was clear, and it was hopeful. Destiny, in this framing, played a smaller role than habit.
More recent twin research has begun to complicate that picture. A study published in Science in early 2026 — drawing on twin databases from Sweden and Denmark, and including for the first time a cohort of twins raised in separate households — suggested that the genetic contribution to lifespan may be meaningfully higher than earlier estimates indicated. By separating genetic inheritance from shared environmental influence more precisely than previous studies had managed, the researchers concluded that genetics may account for roughly half of the variation in how long people live. That is approximately double what the field had long assumed. The full study is available via the journal publication.
The finding has traveled through the research community with the weight of a recalibration. It does not mean that longevity is predetermined — the researchers themselves were careful on this point. It means that the genetic dimension of aging may have been systematically underestimated, and that the picture of what shapes a lifespan is more biologically complex than the simpler lifestyle narrative had suggested. What the study also confirms, quietly, is that roughly half of the variation is not explained by genetics — which is precisely the territory that the science of healthy aging has always focused on, and the territory we explored in depth in our article on the health span gap. These observations come from independent research and do not involve any specific Codeage product.
Genes may shape roughly half the story.
The other half — the modifiable half — is where
the science of healthy aging has always lived.
The Research Context
Two halves of a lifespan — and what researchers have associated with each.
These estimates are drawn from twin research analyzing populations across multiple countries. They represent population-level associations and should not be interpreted as fixed percentages for any individual. The science here is evolving, and different studies have produced different estimates depending on methodology and population studied.
The share of lifespan variation some twin studies have attributed to genetic factors
Recent analyses of twin datasets — including twins raised in separate households — have suggested that genetics may account for roughly half of the variation in how long people live. This estimate is approximately double what earlier twin studies had concluded, and has prompted researchers to revisit how much of longevity biology may be inherited rather than acquired.
The share potentially shaped by environment, lifestyle, and the biological inputs a life accumulates
The other half — whatever its precise proportion — is the territory that longevity science has organized itself around. Exercise, sleep, nutrition, stress regulation, inflammation, and the cellular systems that govern repair and maintenance over time. This is the half where decades of research have found the most consistent associations with healthy aging outcomes. It is also the half where choices, accumulation, and sustained support may make the most difference.
Figures represent population-level estimates from a 2026 twin study published in Science, analyzing twin databases from Sweden and Denmark including twins raised in separate households. Research was conducted independently and does not involve any specific Codeage product. Estimates vary across studies; the precise proportion attributed to genetics remains an active area of scientific inquiry. Read the full study →
II
What the genetic half may contain —
and why it does not close the conversation.
Understanding what the genetic contribution to lifespan actually means requires some care. Genetics does not operate as a single switch. What researchers have identified is a distributed picture — thousands of common genetic variants, each contributing a small effect, whose combined influence may shape the biological systems that govern aging over a lifetime. No single gene has been found to reliably determine longevity in humans. The genetic signal is real, but it is diffuse.
Research on populations of exceptionally long-lived people has offered one of the most instructive windows into this question. When scientists have compared the genomes of people who reached advanced age without major chronic disease to those of the broader population, the findings have been striking for what they failed to find as much as for what they did. The genetic differences, in most such studies, have been relatively modest. What distinguished the long-lived cohorts was less a specific genetic advantage than an absence of high-risk variants in combination with the accumulated behavioral and biological factors that the broader longevity literature has most consistently highlighted. Genetics may set a range. What a life does within that range appears to matter considerably.
The recalibration toward a higher genetic estimate does not therefore argue for fatalism. It argues for a more sophisticated understanding of what the biology of aging actually involves — one in which the genetic dimension is taken seriously, and in which the modifiable dimension is understood not as a simple override of genetics but as the layer of biology that shapes how genetic tendencies actually express themselves over time. These are not competing explanations. They are two parts of the same system. Research was conducted independently and does not involve any specific Codeage product.
The Genetic Dimension — What Research Has Described
Three things research has associated with the genetic contribution to aging — and how each is understood.
01
DNA repair capacity — how efficiently the genome maintains itself over decades of replication
Research has associated genetic variation in DNA repair pathways with differences in how well the genome maintains its integrity over decades. Some long-lived populations have been found to carry variants associated with more efficient DNA repair — suggesting that the rate at which genomic damage accumulates may have a heritable component. This is one of the more mechanistically plausible connections between genetics and longevity that researchers have described. Studies were conducted independently and do not involve any specific Codeage product.
02
Inflammatory baseline — how the immune environment is calibrated across a lifetime
Studies of centenarians have consistently noted associations between exceptional longevity and a lower baseline of chronic systemic inflammation. Some of this association may reflect heritable differences in immune calibration — the set point at which the inflammatory system operates. Genetics may influence whether a person's baseline tends toward chronic low-grade activation or toward a more regulated immune environment. What researchers have also found is that lifestyle inputs — particularly diet, physical activity, and sleep — appear to influence this baseline considerably, suggesting that genetic tendency and behavioral input interact. Studies were conducted independently and do not involve any specific Codeage product.
03
Metabolic efficiency — how well cellular energy systems function across the decades
Mitochondrial function, insulin sensitivity, and the broader efficiency of cellular energy metabolism have all been associated with longevity outcomes in the research literature. Some of this variation may be heritable — reflecting genetic differences in how the metabolic machinery of cells is constructed and regulated. But metabolic efficiency is also among the biological dimensions most studied for its responsiveness to lifestyle inputs: physical activity, nutritional quality, and the cellular support systems that research has associated with NAD+ biology and mitochondrial health. The genetic tendency may set a starting point; the inputs may determine where it goes from there. Studies were conducted independently and do not involve any specific Codeage product.
The Modifiable Half — Where Longevity Science Has Focused
Four dimensions researchers have most consistently associated with how the modifiable half may be shaped.
The biological systems that govern cellular repair, DNA maintenance, and the clearance of damaged cellular components — including autophagy and the mitophagy process that removes dysfunctional mitochondria — appear to be meaningfully responsive to inputs rather than fixed by genetics alone. Research has associated NAD+ availability, sirtuin activity, and the broader cellular maintenance machinery with aging outcomes in ways that suggest these systems are active dimensions of the modifiable half. Their efficiency may be influenced by nutritional status, metabolic inputs, and the degree to which the biology underlying them is supported over time.
Research was conducted independently and does not involve any specific Codeage product.
Chronic low-grade inflammation — sometimes described in the research literature as inflammaging — has been consistently associated with age-related decline across multiple organ systems. Research has associated higher baseline inflammatory markers with earlier onset of the chronic conditions that define the health span gap. This inflammatory baseline appears to be shaped by genetics but also substantially modifiable: the gut microbiome, dietary patterns, physical activity, sleep quality, and stress regulation have all been studied in connection with how the systemic inflammatory environment is calibrated over time.
Research was conducted independently and does not involve any specific Codeage product.
The preservation of muscle mass, metabolic efficiency, and physical capacity across the decades has been among the most robustly studied predictors of healthy longevity in the research literature. These dimensions appear to respond to inputs more directly than many other aspects of aging biology — with physical activity, adequate protein intake, and the cellular biology supporting energy metabolism all showing associations with better-preserved function in later life. Genetics may influence the trajectory; the inputs appear to shape where on that trajectory a person actually lands.
Research was conducted independently and does not involve any specific Codeage product.
The connective architecture of the body — collagen-dependent joint function, bone density, skin integrity, and the broader structural resilience that physical capacity depends on — undergoes predictable changes with age that appear to be accelerated or slowed by inputs rather than fixed entirely by genetics. Collagen production capacity changes with age, and the rate at which that change proceeds may be influenced by nutritional status, physical activity, and the degree to which the structural systems of the body are supported across the middle decades of life — the period when the biology that determines later structural health is most actively in motion.
Research was conducted independently and does not involve any specific Codeage product.
The Research in Context
Three things the science has found
worth holding onto.
~2×
The approximate increase in estimated genetic contribution to lifespan suggested by the 2026 twin study from Sweden and Denmark, compared to earlier estimates
Earlier twin studies had suggested genetics account for perhaps 25% of lifespan variation. The 2026 study — analyzing twin databases from Sweden and Denmark, including twins raised in separate households — suggested the figure may be closer to 50%. Including twins raised apart allowed researchers to more cleanly separate genetic inheritance from shared environmental influences. The revision does not diminish the modifiable half; it recalibrates the genetic half. Research was conducted independently and does not involve any specific Codeage product. Full study →
No single gene
What researchers studying the genomes of exceptionally long-lived populations have consistently failed to find: a genetic secret to longevity
Studies of people who reached their 80s and 90s without major chronic disease have repeatedly found that the genetic differences between them and the broader population are modest and distributed. There is no longevity gene. The genetic signal is real but diffuse — and what distinguished the long-lived cohorts consistently included behavioral and biological inputs alongside whatever genetic tendencies they carried. Research was conducted independently and does not involve any specific Codeage product.
Midlife
The period researchers have most consistently associated with when the modifiable inputs to healthy aging may have the greatest biological leverage
Research on healthy aging has increasingly focused on midlife as the period when the cellular and systemic changes associated with the health span gap are already in motion — but still most responsive to the inputs that may shape their trajectory. The question of when the modifiable half is most modifiable is itself an active area of investigation, and the answers are pointing consistently toward the decades well before clinical symptoms appear. Research was conducted independently and does not involve any specific Codeage product.
III
What this means for how
the modifiable half is approached.
The recalibration of the genetic estimate does not diminish the importance of the modifiable half. If anything, it sharpens it. Knowing that genetics plays a larger role than previously assumed makes the question of what to do within one's genetic range more rather than less important. A higher genetic contribution means a greater need for the biology that sits on the other side of the equation to be doing its work — consistently, over time, and across the multiple dimensions that longevity research has identified as most relevant.
Those dimensions are precisely what The Longevity Code was organized around. Not because genetics are irrelevant — they are not — but because the modifiable inputs to healthy aging are where sustained attention is most likely to make a difference. The daily nutritional baseline. The structural architecture that physical capacity depends on. The cellular biology of NAD+ and mitochondrial health. The systemic coordination of gut, brain, and metabolic function. These are not alternatives to genetics. They are the biology that operates in the space genetics leaves open — and the space, as the research increasingly suggests, may be roughly half the picture.
For more on the specific cellular biology researchers have most closely associated with healthy aging, the health span gap article explores how the distance between health span and lifespan may be shaped by the biology of the modifiable half. For the full framework, The Longevity Code hub maps all four pillars and the research behind each one.
Genetics may set the range.
The modifiable half determines
where within that range a life lands.
The Longevity Code · Codeage
Built for the half
that is still yours to shape.
The Longevity Code is the framework Codeage built around the four biological dimensions that longevity research has most consistently associated with the modifiable half of healthy aging.
Explore The Longevity Code →
