Living a long, healthy life is sometimes framed as the outcome of daily choices, but a new study suggests genetics play a bigger role than previously thought.
Standard advice for staying healthy longer includes exercising more, eating healthy food, having regular medical check-ups, sleeping well, drinking less and quitting smoking.
But new research by scientists at the Weizmann Institute of Science in Israel suggests, after removing deaths caused by external factors, genetics influence around 55 per cent of a person's lifespan.
Published in the journal Science, the new findings are based on mathematical modelling, drawing on more than a century of data from twins in Sweden and Denmark, countries with high living standards and relatively equal access to healthcare.
The authors of the new peer-reviewed research claim longevity genes can reveal ageing mechanisms and inform medicine. However, they point out the previous estimates of how much genetics influence life expectancy were confounded by external factors of mortality — accidents or infectious diseases — and therefore contributed to scepticism about the role of genetics in ageing.
According to the researchers at the Weizmann Institute of Science, most lifespan studies previously used data on cohorts of the population born in the 18th and 19th centuries, which were periods of high mortality caused by external factors.
In order to separate external factors from "intrinsic", mostly shaped by genetics, the researchers ran simulations of the two mortality models. They then tested their conclusions on three different twin studies.
As a result, they found, external mortality caused systematic underestimates of the link between genetics and longevity. While previous estimates put heritability at only 20 to 25 per cent, the new results showed genetics influence around 55 per cent of a person’s lifespan.
"The study ... has important consequences for ageing research," wrote Daniela Bakula and Morten Scheibye-Knudsen, researchers at the University of Copenhagen, in a related Perspective article published in Science.
They said the findings give researchers good reason to identify genes linked to longer lives and to better understand the biological processes behind ageing.
Dr Jack da Silva, an evolution expert from the University of Adelaide, said the new study adds to previous research in lifespan heritability observed in other species.
"This is an impressively thorough study. We’ve known for quite some time that there is a lot of genetic variation for lifespan in populations of organisms such as fruit flies studied in the laboratory, and that single genes can have a very large effect on lifespan in these organisms," De Silva said.
"The present study usefully shows that the same is true for humans. The study is also valuable in teasing out the effects of things that can kill us that aren’t age-related, such as accidents and infections, which has been a difficult task in the past."
Context dependent
Professor Tony Blakely, epidemiologist at the Melbourne School of Population and Global Health at the University of Melbourne, told SBS News the study was interesting, but "not too surprising".
"Because we know that you inherit risks for cancer. So for example, breast cancer has an inheritability, colorectal cancer has an inheritability, cardiovascular disease has some level of inheritability. So of course, therefore, some of the variation between us humans is going to be due to genetics."
Blakely said variations in the environment can play a significant role.
"If you live in a place where half the people smoke, half the people don't, where there's really bad diets amongst some people, and really good diets amongst others, where half the population lives in really polluted cities, you've got more environmental variability. That will drive the overall variability of how long people are likely to live," he said.
He added that, in the Scandinavian countries that were studied, just like in Australia, some of the environmental determinants have been reduced.
"In Sweden or Denmark, and in Australia to a large extent, where we've reduced some of those environmental determinants or tried to squash them out. Then things like genes start to come out a little bit more as explaining some of the residual difference between humans and how long we might live."
However, Blakely says countries such as Denmark or Sweden are more homogeneous than Australia, and longevity rates would be context-dependent.
"In a population like Australia with different countries of birth, different ethnicities, different socioeconomic groups, you might see more variability because the environment is causing more variability, not just genes causing how long you live."
In Australia, life expectancy has increased by over 30 years since 1900.
Blakely says that this was not because genetics changed.
"That's because of improving diets, reduced smoking, better sanitation — all those things. And so what drives how long a population lives on average is the environment. But within wherever your population is, at some point in time, there will be variability in that due to genetics, as well as other variability that's due to things like whether you smoke or not."
Life expectancy for females born between 2021-23 is now 85.1 years, and for males it's 81.1 years, according to figures from the Australian Institute of Health and Welfare.
Do lifestyle choices influence longevity?
Blakely said lifestyle choices, as well as access to quality health care, are critical to living longer.
"The quality of your diet, physical activity, alcohol consumption, sodium consumption, eating the fruit and vegetables, all that stuff still matters, and will be driving a lot of our own life expectancy."
He said it’s not just about genetics and healthy habits. Sometimes it's also about luck.
"There's a certain amount of chance whether your gene is going to do a mutation and cause a cancer that's not inherited that happens as you get older," he said.
"So of course, lifestyle matters a lot. And so does the quality of our health services and treatments. We have treatments now that can save lives or prevent illness as well."
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