Genes vs. lifestyle: Which has greater impact on how long you live?

Life is precious, and many of us try to do everything “right” to live longer. We eat better, move more, avoid pollutants, guard our sleep, manage stress, and take supplements. The prevailing belief is simple: how long you live mostly depends on your lifestyle. Very few people instinctively point to their genes. But a new study suggests your genes may have a much bigger role than previously thought. By how much? Roughly half.

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Your Genes Matter — Maybe More Than We Thought

It’s not controversial to say genetics influences longevity. Most human traits, from height to body fat distribution to disease risk, are partly heritable. But lifespan has long been treated as different.

For decades, twin and family studies estimated that the heritability of lifespan was modest — typically 10% to 25%, with some studies suggesting as low as 6%. That fed the narrative that environment and lifestyle overwhelmingly drive how long we live. The study, published in Science, challenges that assumption, estimating that about 50–55% of the variation in human lifespan can be attributed to genetics once certain confounding factors are accounted for.

“Let’s say I could raise human beings in a lab like I raise mice… and I control their environments. How much do their genes impact their life span?,” biophysicist Ben Shenhar of the Weizmann Institute of Science in Rehovot, Israel, and lead author of the study, told ScienceNews.

That thought experiment — removing environmental differences to see what remains — is what ultimately shaped the team’s analysis.

Instead of lumping all deaths together, researchers separated mortality into two categories: Intrinsic mortality, deaths driven by internal biological processes, like age-related diseases or physiological decline, and extrinsic mortality, deaths caused by external factors such as accidents, violence, infectious disease, and environmental hazards. This distinction matters because many historical datasets, especially twin registries, include people born in the late 1800s and early 1900s, when infectious disease and accidental death were far more common.

If someone died young from tuberculosis or a farming accident, that early death might have little to do with their genetic makeup — yet it would still count in traditional lifespan analyses, weakening the visible genetic signal. At the same time, sanitation, hygiene, and medical care improved over the 20th century, many of these external risks declined, making inherited differences in lifespan easier to detect.

So the researchers built a mathematical model to estimate and subtract extrinsic mortality. They re-analyzed data from large Danish and Swedish twin registries, along with U.S. data that included siblings of centenarians. When they accounted for extrinsic deaths, heritability estimates rose to about 50–55%.

Why Understanding Genes & Lifespan Matters

Understanding how much of lifespan is shaped by genes helps us better understand aging itself. It may explain why some people who carefully follow every health rule still develop disease or die relatively young and why some centenarians reach extreme old age without the meticulous routines that today’s biohackers swear by. “They have protective genes that protect against the harms of age,” Shenhar said.

“Some people follow every rule in People magazine and still can’t lose a pound. Others sleep eight hours and wake up exhausted. Genetics explains more of those differences than most people realize,” Dr. Gabriel Alizaidy, a longevity and precision medicine expert, told Nifty50+.

The study also touches on a bigger question: If lifespan were almost entirely genetic, then lifestyle changes like eating well, exercising, managing stress, even pursuing anti-aging treatments might matter far less than we think. But if the environment dominates, then those daily choices become even more powerful.

This study suggests the answer isn’t either-or.

“Some people follow every rule in People magazine and still can’t lose a pound. Others sleep eight hours and wake up exhausted. Genetics explains more of those differences than most people realize,” — Dr. Gabriel Alizaidy, a longevity and precision medicine expert

Still, this does not mean there is a rigid, genetically coded expiration date stamped on each of us. “Fifty percent heritable” doesn’t mean your lifespan is 50% fixed at birth. It doesn’t divide your life into neat halves — genes versus lifestyle. Instead, it means that, within a given population and set of living conditions, about half of the differences in how long people live can be linked to genetic variation.

Not all causes of death are equally genetic, either. Dementia and cardiovascular disease appear to show stronger heritable influence, while cancer shows lower heritability, suggesting that some age-related conditions may be more shaped by environment or random mutations than others.

You’re born with genes you can’t change, but genes don’t act alone. If roughly half of lifespan variation reflects environment, lifestyle, healthcare, and chance, that leaves meaningful room for influence. Your genetic makeup may give you a slight edge — or place you at higher risk for certain diseases — but it doesn’t seal your fate.

Alizaidy suggested getting a comprehensive blood panel. “One that goes deeper than your standard annual labs and actually looks at your hormone levels, inflammation markers, and metabolic health tells you more about how your specific body ages than any generic health magazine ever will.”

But getting the data is only the first step. He noted that pairing it with a clinician who specializes in aging biology can help interpret the results and build a plan around your biology, not a template built for everyone else.The environment you grow up in matters, too: whether you were raised in a family of early risers, home-cooked meals, and weekend hikes, or in one shaped by stress, poor nutrition, or limited access to care. Those patterns can influence your health just as profoundly as inherited DNA.

And beyond upbringing, your daily choices, what you eat, how you move, whether you smoke, how you manage stress, remain firmly within your control.