When research tells us that our grandparents' diets can affect our health decades later, it can be hard to shake the feeling that genetics spells out the trajectory of our wellbeing.
But how much of our health is actually determined by our genes, and what effect does our lifestyle have, for better or worse? Can we really overcome the genetic cards we've been dealt and extend our lives by eating well and exercising often, as some research suggests?
A new study of more than 350,000 people from the UK has found that healthy lifestyle choices could offset the genetic risk of dying young by as much as 62 percent.
"To our knowledge, our study is the first to investigate the joint association of genetic risk and lifestyle factors with human lifespan," the researchers write in their published paper.
Previous epidemiological studies have looked at one or the other, but with data from three large, long-term population studies investigating the links between genetics, environment, and disease, this new study could compare the effect of genetic risk and lifestyle factors on longevity simultaneously.
The team of researchers from several universities in China and the University of Edinburgh in the UK analyzed data on more than 350,000 adults of European descent, who were recruited to the UK Biobank study from 2006 to 2010, and followed for a median of almost 13 years.
The participants were asked about their diet, physical activity, smoking, alcohol intake, body shape, and sleep duration, and grouped into three tiers based on their responses. The researchers also split participants into three categories based on known genetic risk factors called polygenic risk scores – drawn from US studies – affecting lifespan.
Similar to previous family studies, the researchers found that genetics alone can raise the risk of early death by 21 percent.
An unhealthy lifestyle featuring poor sleep, little exercise, processed food, cigarettes, and alcohol was also linked to a 78 percent greater risk of dying early, regardless of someone's genetic predisposition.
People with an unhealthy lifestyle and a genetic predisposition to a shorter lifespan were twice as likely to die from non-accidental, non-COVID related conditions during the study period as those with a lower genetic risk and more favorable lifestyle habits.
But opting for a healthier lifestyle – mainly by not smoking, exercising regularly, eating well and getting enough sleep – offset the genetic risk of a shorter life by 62 percent, the researchers found.
"This study elucidates the pivotal role of a healthy lifestyle in mitigating the impact of genetic factors on lifespan reduction," the researchers conclude.
This is an observational study, however, so no firm conclusions can be drawn about cause and effect. Most of the participants were of white-European ancestry, so the findings can't be generalized to other populations either.
What's more, participants were surveyed about their lifestyle at only one point in time, when they joined the study, and the genetic variants studied captured only a small fraction of the genetic risk associated with a shorter lifespan, so there could be much more DNA in play.
Another big question this study touched on only briefly is at what age people make positive changes to their lifestyles.
The analysis found that people with a high genetic risk of a shorter life could add roughly another 5 years to their life expectancy at age 40 if they had implemented lifestyle changes. Other research shows the importance of maintaining them.
"Given that lifestyle behavioral habits are usually developed before middle age, taking effective public health interventions is quite crucial for those at high genetic risk to extend their lifespan before the formation of a fixed lifestyle," the researchers conclude.
The study has been published in BMJ Evidence-Based Medicine.