Young doctors’ bodies age six times faster than normal because of the stress of the job, according to new research.
The study shows that long working hours speed up the shortening of telomeres – caps on the end of chromosomes that protect our cells.
They’ve been likened to the plastic tips of shoelaces – and are believed to be key to longevity.
Samples of DNA from medical students in their first year of hospital residency , or intern, found dramatic shrinkage.
Some were putting in more than 80 hours a week – and they were suffering the greatest damage to their ‘biological age.’
Senior author Dr Srijan Sen, a neuroscientist at Michigan University in the US, said: “Research has implicated telomeres as an indicator of ageing and disease risk.
“But these longitudinal findings advance the possibility telomere length can serve as a biomarker that tracks effects of stress – and helps us understand how stress gets ‘under the skin’ and increases our risk for disease.”
Telomeres are fragments of DNA which cap both ends of each chromosome and protect against the wear and tear of natural ageing.
The discovery, published in the journal Biological Psychiatry, suggest the importance of ongoing efforts to reduce the strain of medical training.
It also has implications for other professions and situations that expose people to prolonged stress and months of long hours.
Dr Sen said: “It will be important to study how telomere changes play out in larger groups of medical trainees, and in other groups of people subjected to specific prolonged stresses such as military training, graduate studies in the sciences and law, working for startup companies, or pregnancy and the first months of parenting.”
The participants provided two samples – one before starting their intern and the other 12 months later.
They also filled out a lengthy questionnaire at various time points that revealed the more hours they put in the smaller the telomeres became.
It’s the first study of its kind to measure telomere length before and after individuals faced a common prolonged intense experience.
It involved 250 interns from around the US who volunteered for the Intern Health Study headed by Dr Sen and a comparison group of Michigan students.
The results showed some new doctors went into residency with telomeres that were already shorter than their peers.
This included those who said their family environment early in life was especially stressful – which echoes previous findings about the impacts of such an upbringing on telomere length.
Those who scored high on personality traits that together are classed as “neuroticism” – being quick to react and slow to relax, and a tendency to respond with negativity – also had shorter telomeres at the start of intern year.
But when the team looked at the results of the DNA tests taken after intern year ended, only one factor that they studied emerged with a clear link to telomere shrinkage – the number of hours the interns worked each week.
On average, all the interns in the study said they worked an average of 64.5 hours a week.
But the more the interns worked, and therefore the more days they put in that were at or above the national limit of 16 hours in effect at the time, the faster their telomeres shrank.
Dr Sen said: “The responses given by some of the interns in these surveys indicated that some were averaging more than 80 hours of work a week, and we found that those who routinely worked that many hours had most telomere attrition.
“Those whose hours were at the lower end of the range had less telomere attrition.”
By contrast, the comparison group of 84 first-year undergraduate students experienced no telomere shrinkage.
This was despite also being in a stressful year-long situation of coping with life at an elite institution of higher education.
First author Dr Kathryn Ridout, of Brown University in Rhode Island, said: “The current model of intern year training during residency increases trainee stress, which impacts their mental health and wellbeing.
“These results extend this work and are the first to show this stress reaches down to the biological level impacting the well accepted marker of ageing and disease risk – telomere length.
“I was particularly surprised to see the relation of number of hours worked to telomere shortening.”
The discovery telomeres protect the DNA in chromosomes from damage earned the 2009 Nobel Prize.
Since then research in humans has focused on taking snapshots of telomere length – mainly in older adults, said Dr Sen.
This has yielded important breakthroughs about the links between shrunken telomeres and disease.
Dr Ridout pooled data from dozens of telomere studies for a study published in 2016 that connected their length to the risk and severity of depression.
She hopes her latest results will be heeded by the Accreditation Council for Graduate Medical Education and others.
Dr Ridout added: “Having completed residency myself and understanding the stress that can come with this training and extended work hours, I am hopeful these data can help inform the decisions of governing bodies that have been debating the importance of regulating resident work hours.
“Our results suggest that reforms in intern training and work hours with a renewed focus on well-being is necessary to protect the health and viability of our physician workforce.”