Across families and generations, some people edge past 90 while others are gone far earlier, despite similar lives.
New research on thousands of Nordic twins suggests that the answer sits right between our DNA and our daily habits, challenging long‑held assumptions about how much control we really have over our own lifespan.
Genes and lifestyle share the steering wheel
For years, public health messages pushed a simple idea: live well, live long. Eat better, move more, quit smoking, manage stress. Genetics, many experts said, explained only a modest slice of human longevity – roughly a quarter.
A fresh look at historical twin records now paints a sharper, more uncomfortable picture. Our genes may account for roughly half of the variation in how long we live, once early deaths from accidents and infections are stripped away. Lifestyle still matters hugely, but it is no longer the lone star of the story.
New analyses of Nordic twins born between 1870 and 1935 suggest that about 50–55% of lifespan differences stem from inherited biology.
This does not mean length of life is fixed at birth. Instead, it suggests that once societies remove many external threats – unsafe water, rampant infections, dangerous work – the quiet pull of genetics becomes more visible.
What the Nordic twin study actually did
The twin data that underpins this shift is not new. What is new is how scientists decided to treat the causes of death. Earlier work tended to throw every death into the same statistical basket. A fatal infection at 35 was weighted alongside a gentle passing at 92.
In the recent reanalysis, researchers separated deaths into two broad categories:
- Deaths linked to ageing itself (so‑called intrinsic mortality)
- Deaths driven by outside events such as accidents, violence or acute infections
By focusing on intrinsic mortality, the team tried to isolate the ageing process from random misfortune. Among the thousands of twin pairs, they then compared lifespans within each pair, while accounting for the environment they shared as children and, in many cases, as adults.
When early, random deaths were removed, similarities in lifespan between twins increased, pointing to a stronger genetic influence than previously estimated.
➡️ When an oral infection sneaks into cancer development
➡️ In minutes, AI now does what medical teams needed months to complete
➡️ A hidden tunnel has linked Earth to distant stars for millions of years
➡️ A study suggests cats can develop a form of dementia similar to Alzheimer’s
➡️ Cannabis drinks open an unexpected path in the fight against alcohol
➡️ This diabetes drug might actually slow down time itself
➡️ Brain rejuvenation is measurable in adults who move more
➡️ Physical exercise: a remedy as effective as medication against depression
The result: hereditary factors appeared to explain around 55% of the variation in lifespan across the cohort, more than double the classic 25% figure that has guided thinking for decades.
Why earlier estimates missed part of the story
Historical records from the late 19th and early 20th centuries are full of tragedies that had little to do with personal biology. A contaminated milk batch could wipe out a cluster of children. A factory accident might end the life of a robust young adult.
When such deaths are counted alongside age‑related decline, the genetic signal gets blurred. Two twins might share a strong genetic potential for long life, but if one died in a flu epidemic at 28, the data would misleadingly suggest weak genetic influence.
By excluding these premature, largely random deaths, the new analysis uncovers a starker pattern. Twins who both lived past the most dangerous decades tended to age in more similar ways, supporting the idea that underlying biological differences drive a significant share of lifespan variation once external chaos is reduced.
Richer countries, clearer genetic effects
One striking implication concerns modern, stable societies. As vaccinations, sanitation and occupational safety improved through the 20th century, the role of bad luck gradually shrank. Researchers argue that, under these safer conditions, genetic differences become more apparent.
In wealthy and politically stable countries, the environment becomes less deadly, giving inherited traits more room to shape how long we live.
This does not erase the influence of lifestyle, pollution or inequality. It simply shifts the balance: when everyday life is less hazardous, biology stands out more clearly in the statistics.
Ageing, disease and the mixed role of heredity
The twin research connects with a broader effort to untangle which age‑related diseases are strongly hereditary and which are more stochastic or environmental.
Current evidence suggests that conditions such as cardiovascular disease and some forms of dementia have a notable genetic component. Family history often hints at elevated risk. By contrast, many cancers appear more sensitive to chance mutations and external exposures, such as tobacco smoke or UV radiation.
| Condition | Typical genetic influence | Key external factors |
|---|---|---|
| Heart disease | Moderate to high | Diet, exercise, smoking, blood pressure |
| Dementia (e.g. Alzheimer’s) | Moderate, higher in some families | Education, head injury, vascular health |
| Cancer (overall) | Often moderate or low | Smoking, infections, radiation, random mutations |
This patchwork of influences supports a simple but nuanced idea: longevity is not governed by a single “long‑life gene”, but by a web of biological systems interacting with decades of choices and exposures.
What this means for how we live now
Accepting that genes may account for around half of lifespan variation can feel fatalistic. It need not be. The other half is still on the table, and it is significantly shaped by behaviour and public policy.
Genetics may load the gun, but lifestyle and environment often decide whether and when it goes off.
For individuals, the message remains familiar but gains a sharper edge. Diet, exercise, sleep, stress management and social ties all influence how our underlying biology plays out over time. Two people with similar genetic risk for heart disease can end up with very different outcomes depending on smoking, blood pressure control and activity levels.
For governments and health systems, the findings argue for a twin‑track approach. Preventive programmes need to keep targeting common, modifiable risks, while research funding expands into genetic and molecular pathways that slow ageing itself.
From genetics lab to potential therapies
As scientists gain a clearer view of how much of our lifespan is biologically programmed, attention is turning to the mechanisms behind that programming. Several avenues are drawing interest:
- Cellular repair processes that fix DNA damage
- Pathways that control inflammation over many years
- The length and maintenance of telomeres, the protective caps on chromosomes
- Metabolic systems that respond to calorie intake and energy use
Some teams are studying families and individuals who live well past 90 with relatively little disability. Others are using large genetic databases to spot variants linked to slower ageing or resistance to common diseases. The goal is not simply to stretch lifespan, but to extend “healthspan” – the number of years lived in good health.
Key terms that shape the debate
Two technical phrases have become central in this field and are worth clarifying:
- Intrinsic mortality: deaths driven primarily by the biological ageing process, such as organ failure or age‑related disease.
- Extrinsic mortality: deaths caused mainly by external events or agents, like accidents, violence or acute infections.
The Nordic twin study hinges on that distinction. By narrowing in on intrinsic mortality, researchers are trying to see ageing as it is, not as it appears when mixed with random misfortune.
How this knowledge could play out in real life
Imagine two siblings in their 40s. Both have parents who developed cardiovascular disease in their early 60s. Genetic testing shows they share several risk variants linked to high cholesterol and blood pressure. One sibling smokes, rarely exercises and works long, stressful hours. The other eats a relatively balanced diet, runs twice a week and receives regular blood pressure checks.
The shared genes raise both of their baseline risks, but their daily environments push their health trajectories apart. In statistical terms, they share similar “intrinsic” vulnerability, yet very different extrinsic pressures. The new research suggests that if both avoid early non‑ageing deaths, their later‑life outcomes will reflect that underlying biology more clearly than older models predicted.
This kind of scenario underlines the double reality emerging from current research. We may be less free than we hoped when it comes to our upper limit of life, yet we still have substantial influence over how close we get to that limit – and how healthy those extra years feel.
