How long you live may depend much more on your genes than scientists thought

Your lifespan depends on your genes much more than scientists thought

By Cody Cottier edited by Tanya Lewis

Thirty years ago, a famous study of Danish twins revealed that our genes “only moderately” influence how long we live. Longevity, the authors estimate, was about 25 percent hereditary, meaning the remaining three-quarters was determined by environmental factors and lifestyle choices, such as diet and exercise. Most subsequent studies have found heritability to be between 20 and 25 percent, and 25 percent is now widely accepted. But a new study more than doubles that figure, suggesting that lifespan may be more genetically fixed than we thought.

The study, published today in Scienceachieves this dramatic increase by reframing the way scientists think about longevity. Rather than lumping all deaths together, researchers distinguish between two types: “intrinsic mortality” comes from integrated biological processes of aging and genetic mutations, while “extrinsic mortality” comes from external causes, such as accidents and infections. Early longevity studies analyzed groups of people born in an era of widespread extrinsic mortality. This skewed previous estimates of heritability, says Uri Alon, a systems biologist at the Weizmann Institute of Science in Rehovot, Israel, and lead author of the new paper.

To sort out the effects of intrinsic and extrinsic deaths on the heritability of longevity, he and his colleagues performed computer simulations of human mortality, calibrated using data from these previous twin studies. When they reduced extrinsic mortality to zero, leaving only deaths caused by intrinsic aging processes, the heritability of lifespan roughly doubled. Surprised, the team performed a sanity test: Researchers calculated heritability in the traditional way for twins born between 1900 and 1935, a time when rapid medical advances gradually reduced premature deaths. From one generation to the next, Alon says, “they have lower and lower extrinsic mortality, and we see that their heritability increases more and more.” Taken together, the results indicate that intrinsic lifespan – how long a person will live if they do not die from an external cause – is about 55% heritable.

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Kaare Christensen, an epidemiologist and professor at the Danish Twin Research Center at the University of Southern Denmark, who was not involved in the study, calls it “an interesting mathematical exercise” but notes that “in the real world, people die both types of death.” There is no real gap between the two heritability estimates, 25 and 55 percent, he says, because they measure different things. However, given that extrinsic mortality has declined significantly over the past century, Alon argues that “a higher number is more relevant” for people born today. In reality, aside from the most obvious cases of genetic (like a genetic disease) or environmental (like lightning) causes, it is difficult to separate extrinsic and intrinsic factors.

Whether or not the new estimate offers a more realistic picture of the heritability of lifespan, it highlights the importance of genetics in extending life, says Sofiya Milman, a scientist who studies aging and longevity at the Albert Einstein College of Medicine. She is one of many researchers trying to understand how the unique biology of centenarians protects them from age-related diseases. “We hope to create therapies that will mimic these intrinsic factors,” says Milman, “and make them accessible to people who haven’t won the genetic lottery.”

Most of us are unlikely to make it past 100 without the right set of genes – or at least drugs designed to replicate their beneficial effects. However, until such treatments become available, a healthy lifestyle remains the best way to live longer. Even though exercise, sleep and a balanced diet only contribute 45 percent to lifespan, evidence shows they can still add 10 or more years to a person’s life. “These things will benefit you,” Milman says, “regardless of your genetic makeup.”

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