Lifestyle factors play a large role in living a long and healthy life, but scientists say new research may have identified a major indicator of how long you will live.
A study published in the journal Science analysed lifespan and genetics in sets of identical and fraternal twins in Denmark, Sweden and the United States. Researchers compared how closely lifespan matched within each pair of twins.
Because older records did not always clearly state cause of death, the team estimated which deaths were due to external factors such as accidents or infections and which were more likely driven by internal, age-related processes. They found death rates stayed fairly steady between ages 20 and 40, then rose sharply as people got older. Deaths from external causes also increased with age, but not as quickly as deaths linked to internal factors like ageing or inherited risk.
After running the numbers, the researchers concluded that genes may determine up to 55% of your lifespan—more than double some previous estimates. The remaining influence likely comes from environmental factors such as lifestyle and access to healthcare, along with random changes and modifications to genes over time.
Lead study author and researcher on the physics of ageing, Ben Shenhar, says the team made the discovery unexpectedly while refining a mathematical model.
The findings can sound discouraging if you are looking for actionable ways to live longer, but experts say that is not the right takeaway.
Why do genes matter so much?
There are several reasons genetics appears to have such a strong influence. “Much of it is disease risk,” Shenhar says. “We include an analysis of heritability to die from cancer vs cardiovascular disease vs dementia. Death from dementia is most heritable, then cardiovascular, and finally cancer.”
Twin studies suggest genetics accounts for about half of the variation in many human traits, including personality, Shenhar explains. “In that sense, lifespan is not an outlier—rather, it falls within the fold of what we already know about genetic influence,” he says.
However, there is no single “longevity gene”. “Lifespan is influenced by hundreds, if not thousands, of genes—not a select few,” Shenhar says.
Genes also do not act alone, notes integrated medicine and health expert Leigh Frame. “Genes do not operate in isolation,” she says. “They set a range of possibilities rather than a fixed outcome, influencing how individuals respond to environmental exposures, lifestyle behaviours and ageing itself.”
The study has limitations. It relied on Scandinavian twin registries, which means the results may not apply in the same way to people from other populations, points out medical and biosciences expert Dr Leonard E. Egede.
What might this mean for lifestyle factors?
It can be tempting to read this research and think all those years of eating well and going to the gym do not really matter. Experts say that is not the case. “Longevity is a combination of genes, lifestyle and environmental factors,” Dr Egede says.
Even if lifespan is about 50% due to genetics, that still leaves the other 50% influenced by what you do day to day, Shenhar says. “That is where all the usual suspects come in—exercise, diet, social relations, environment and so on,” he says.
Dr Egede agrees. “Poor lifestyle is still an important driver of morbidity and mortality,” he says. “Healthy diet, moderate exercise, stress management and not smoking are key lifestyle modifications that should still be encouraged.”
Following a healthy lifestyle likely matters even more as you get older, Shenhar says. “For example, there is not much difference in mortality between 30-year-olds who drink, smoke and live wildly and those who live well,” he says. “The opposite is true of 80-year-olds. Our environment and lifestyle become more and more important for our health and survival as we age.”
It is also crucial to see your doctor regularly to stay on top of any health conditions that may develop, whether driven by genetics or lifestyle, says internist Dr Janet O’Mahony. “Access to quality primary care may diagnose and treat high blood pressure, diabetes, obesity and high cholesterol,” she says. “Access to cancer screening tests like mammograms and colonoscopies is also felt to save lives.”
While genes lay the foundation, lifestyle plays a major role in your health outcomes. “Even when genetic contributions to lifespan are significant—as much as half according to this research—lifestyle factors remain critically important, especially for healthspan, meaning the years lived in good physical and cognitive health,” Frame says. “In practical terms, lifestyle choices can either amplify genetic vulnerabilities or help buffer against them. While healthy behaviours may not override genetics entirely, they strongly influence how well people age and how long they live free from disease and disability.”
The bottom line
Shenhar stresses that these findings are not a reason to give up on healthy habits. “The message should 100% not be one of genetic determinism,” he says. “I don’t think there are any immediate implications on the personal decision-making level of how to live your life.”
Instead, he says the study highlights how much more there is to learn about the genetics of ageing. “If we can understand what biological pathways underlie the favourable genetic profiles that enable 20% of centenarians to reach age 100 without any serious illnesses, for example, then that could hopefully in the future better guide and fuel research into longevity drugs and interventions,” he says.
Until then, Dr Egede recommends staying focused on what is already proven to support good health. “You can’t control your genes but you can modify your lifestyle,” he says. “Focus on lifestyle modification.”
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