Is Lifespan More About "Genes" Than "Lifestyle"? Is Half of Our Lifespan Determined by Genetics, No Matter How Healthily We Live?

Is Lifespan More About "Genes" Than "Lifestyle"? Is Half of Our Lifespan Determined by Genetics, No Matter How Healthily We Live?

"Is the secret to longevity ultimately 'diet and exercise,' or is it 'genes'?" In an era overflowing with health information, this question has been debated almost like a religious argument. However, at the end of January 2026, a report emerged that seemed to reconfigure the very "premises" of longevity research. The key point is not to simply divide the factors determining lifespan into "genetic or environmental," but to adopt the idea of removing the "noise" that mixes into lifespan data in the first place.


The Issue: The Uniqueness of "Lifespan" as Data

Traits like height, blood pressure, and body fat percentage are relatively easy to estimate for genetic contribution (heritability) through twin studies. However, lifespan is tricky. This is because lifespan is not determined solely by "aging." Accidents, homicides, disasters, toxins, and infectious diseases—events that suddenly occur from outside the body—can mercilessly cut short a lifespan.


Traditional twin studies have often used data from the 19th to early 20th centuries. However, during that time, antibiotics were not sufficient, and deaths from infectious diseases were far more common than today. Even if one identical twin lived to 90 while the other died young from an infectious disease, the result would simply show "different lifespans despite identical genes." Analyzing this as is, one could easily conclude that "environment (luck or era) is more significant than genetics" for lifespan. The way lifespan is "measured" may have underestimated the influence of genes—this is what the current study delves into.


The Key is Statistically Subtracting "Extrinsic Death"

The new analysis considers death by broadly dividing it into two categories.

  • Extrinsic Mortality: Death caused by factors from outside the body, such as accidents, violence, environmental factors, and infectious diseases

  • Intrinsic Mortality: Death associated with biological deterioration within the body due to aging, age-related diseases, and genetic predispositions


Of course, real causes of death are mixed. However, the research team estimated, using mathematical models and large-scale data, to what extent extrinsic deaths "dilute" the correlation with lifespan, even with the constraint that past data do not record causes of death. By correcting for the impact of extrinsic deaths using twin data (Denmark, Sweden) and data on long-lived families in the United States, they found that the heritability of intrinsic lifespan reaches approximately 50-55%.


What this figure implies is not a simple fatalism of "no matter how much you care about your health, your lifespan is determined by genes." Rather, it changes the way we pose the question. The previous "lifespan" was an indicator mixed with signals of aging and noise from extrinsic factors. By weakening the noise from extrinsic factors to view "lifespan closer to aging itself," the genetic contribution appears larger than imagined.


What Changes with "55% Genetic"?

The impact of the research is not just in the size of the numbers. It offers a different answer to the dilemma that longevity research has long faced—the suspicion that "humans are more complex than animal experiments, and the genetic influence might be weaker." In experimental animals, high heritability of lifespan has been known. If humans were an extreme "exception where genetics doesn't apply," the aging mechanisms found in animals would have less guarantee of applying to humans. The current estimate reinforces the view that "humans might not be an exception," potentially affecting investment decisions and research strategies in aging research.


On the other hand, the other half of lifespan is "beyond genes." Diet, exercise, sleep, smoking, drinking, medical access, socioeconomic status, human relationships, stress, and chance. Here lies the room for intervention. In other words, the greater the genetic contribution, the more important it becomes to see "how close we can get by optimizing the environmental side."


Counterarguments and Cautions: Extrinsic and Intrinsic Cannot Be Neatly Separated

As this type of research becomes widespread, caution is simultaneously emphasized. The biggest issue is the "boundary between extrinsic and intrinsic death." For example, infectious diseases cannot be completely labeled as "external" like accidents. Genetic factors may be involved in whether one becomes severely ill from an infectious disease, such as the strength of immune response, presence of underlying conditions, inflammation control, and tendency for thrombosis. Therefore, if infectious diseases are subtracted entirely as extrinsic, it might overly exclude the genetic influence. Researchers and experts speak cautiously on this point.


Another issue is the "difference in what is being measured." The traditional estimate (around 25%) and the current estimate (around 55%) are not about which is correct or incorrect. The former strongly considers real lifespan (including extrinsic factors), while the latter focuses on a hypothetical lifespan excluding extrinsic factors (intrinsic lifespan). On social media, it tends to ignite with "They used to say 25%, and now they've changed their tune again!" but it's more constructive to understand this as a "difference in scale."


Social Media Reactions: Fatalism vs. Behavioralism, and the View on Longevity Business

When the topic is "genes" and "lifespan," social media sways noticeably. This time, reactions were divided into three main streams.


1) Spread of "Fatalism": Is Effort Futile?
Voices like "If half is determined by genes, are all health methods useless?" and "In the end, it's just a lottery of parents" stand out. The stronger the numbers, the more they resonate mentally. However, this interpretation tends to overlook that the remaining half is "beyond genetics" and that the study deals with a special indicator called "intrinsic lifespan."


2) "Behavioralism" Counterattack: That's Why Prevention Works
On the other hand, there is a positive take spreading, such as "If genetics are strong, we can know early about diseases we're prone to and take measures" and "It's because we've reduced extrinsic factors (accidents, infections) that genetic differences have become visible." Genetic information becomes material not for resignation but for enhancing the precision of actions.


3) View on "Longevity Business": How Do Influencers Speak?
As the market for longevity supplements, self-prescribed drug protocols, and biohacking expands, reactions have emerged questioning whether the result of "genes being significant" is inconvenient. Conversely, there's a flow finding business opportunities in "if genetics are significant, then testing and personalization are paramount." It's characteristic of social media that the "interpretation selling" becomes the point of contention rather than the research itself.


Interestingly, researchers themselves are providing supplementary explanations on social media (mainly X) to try to dispel misunderstandings. They unravel the technical aspects of the paper (extrinsic death correction, generational differences in twin data) for the general public and explain "what's new and what hasn't changed." This is symbolic of an era where the distance between research and public relations has shortened.


Health Strategy in the Era of "50% Genetic": The Conclusion is "Ordinary Things" Are Strong

So, what should we do? The conclusion is surprisingly modest. Even if genetics account for half, the other half is influenced by the environment. Moreover, environmental improvements raise "healthy lifespan (the period you can stay healthy)" before "lifespan." Even if you can't score a perfect 100 with genetics, you can avoid failing with lifestyle habits. This remains unchanged.


Furthermore, reducing extrinsic deaths (traffic safety, infection control, work environment, medical access, poverty measures) is a "societal health policy" that cannot be managed by individual efforts alone. The irony and evidence of progress lie in the fact that as extrinsic factors decrease, genetic differences become more visible. Therefore, it becomes more important than ever to consider how to support lifespan as a societal system, rather than relying solely on "personal responsibility."


Conclusion: It's Not "Genetic or Environmental" but "Which Lifespan to Measure"

The essence posed by this study is not "genetic victory/environmental victory." Discussions about lifespan can change significantly depending on how it is measured. Whether discussing "real lifespan" including extrinsic factors or "intrinsic lifespan" closer to aging. If we focus only on numbers without being aware of this difference, social media quickly gets pulled into fatalism and business discussions.


Half is Genetic. But Half Remains. And within that half, not only individual habits but also the design of societal safety and healthcare are included. The update in longevity research is not to predict "how long you will live" but to more accurately ask "why we age" and "how can we delay diseases associated with aging." We want to update the form of the question itself without being swallowed by the impact of the numbers.


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