Young people who smoke and have other unhealthy lifestyle practices age faster biologically than peers without these habits, according to a study that followed 800 teenagers for a decade and assessed markers of ageing in their blood.
“I think if teenagers knew that things like smoking actually made them biologically older, it would motivate them to stay healthy,” says at the University of Jyväskylä in Finland, who led the research.
We normally think of age in terms of number of birthdays – our so-called chronological age. But the biological age of our bodies depends on how much cell damage we have accrued over time.
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Previous studies have found that factors like smoking and can accelerate biological ageing, but they have mostly been done in older adults.
To find out if being unhealthy as a teenager also speeds up ageing, Kankaanpää and her colleagues analysed data from a study of 5000 twins in Finland.
The twins were asked to report their height and weight and how often they smoked, drank alcohol and exercised when they were 12, 14 and 17 years old. Blood samples were then taken for 824 of the participants when they were 21 to 25 years old to study their DNA.
Kankaanpää and her colleagues calculated each participant’s biological age using several “epigenetic clocks” that look for patterns of markers on DNA called methyl groups that correlate with age.
The 16 per cent of participants who had the unhealthiest lifestyles as teenagers – meaning they smoked daily, regularly drank alcohol and rarely exercised – were found to be 1.7 to 3.3 years biologically older by the time they reached their 20s than the 75 per cent who had been moderately healthy or very healthy.
The most overweight teenagers – those whose body mass index (BMI) values were in the top 10 per cent – were 1.8 to 2.4 years biologically older by their 20s than their non-overweight counterparts.
Overall, the participants with the unhealthiest lifestyles and highest BMIs were found to age between two and five weeks faster per year than their healthier peers.
Because the study participants were all twins, the researchers were able to determine that about 60 per cent of the variation in biological ageing was explained by genetic factors and the rest by environmental factors, including lifestyle.
A limitation of the study is that it relied on self-reports of lifestyle, which can be problematic because people don’t always tell the truth, says at Murdoch Children’s Research Institute in Melbourne, Australia. “However, the results do make intuitive sense because we know that people who smoke, for example, often look old for their age,” he says.
“What’s interesting is how quickly the effects of the unhealthy lifestyles showed up – they were already there by the age of 21,” says Novakovic.
Being unhealthy during adolescence may be particularly damaging because it is a time of rapid growth, which could have a magnifying effect on biological ageing, says Kankaanpää. “I think that more health interventions should be targeted toward teenagers, especially because the choice about whether to start smoking is typically made at this age,” she says.
Whether it is possible to undo the biological ageing effects of unhealthy teenage years by having a health makeover later on is still unknown and would require further research, says Kankaanpää.
medRxiv
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