Interned Out: New Doctors’ DNA Ages Six Times Faster Than Normal During First Year

ANN ARBOR, Mich. — Many physicians may tell you that a career in medicine was in their DNA, but they probably weren’t aware of exactly what that career was doing to their DNA. The first year of residency, also called the intern year, is well known for being a new doctor’s most intense year of their rigorous training. Just how physically taxing is it? A new study shows that during this brutal first year, doctors’ DNA ages six times faster than normal.

Researchers at the University of Michigan’s School of Medicine say the longer the hours worked during these training programs, the larger the effect. That’s the conclusion doctors reached after measuring the doctors’ telomeres, the segment of DNA strands which keep the ends of chromosomes intact, akin to the cap-like plastic ends of shoelaces. Telomeres shrink as we get older, but the rate of shrinkage among medical interns suggests it would be wise to keep stress as low as possible during medical training.

The study included 250 medical interns from medical facilities throughout the United States. Researchers measured the interns’ telomeres before and after their intern year, and compared the results with those from a group of students who volunteered for the study at the University of Michigan. It’s the first study of its kind to measure individuals’ telomeres before and after a long-term, stressful experience.

“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 that this stress reaches down to the biological level, impacting the well accepted marker of aging and disease risk, telomere length,” says the study’s first author, Dr. Kathryn Ridout, in a university release.

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In addition to providing Dr. Sen and his team with a DNA sample before and after they started their intern year, the study participants also filled out long questionnaires about their work schedules and personality traits at various points during the year-long study.

The authors found a direct link between telomere shrinkage and the hours an intern worked each week, which tended to average about 64.5 hours weekly. The more participants worked, however, the faster their telomeres shrank.

“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,” says senior author Dr. Srijan Sen, a neuroscientist and psychiatrist at UM. “Those whose hours were at the lower end of the range had less telomere attrition.”

Of course, some participants began the study with shorter telomeres which researchers attributed to stressful family or personal situations earlier in their lives. Participants who also scored higher on a personality assessment for neuroticism, a trait defined as someone quick to react negatively and slow to relax, also tended to have shorter telomeres.

Researchers found no telomere shrinkage among the undergraduate control group, even considering the rigors of a typical college year.

“Our results suggest that reforms in intern training and work hours with a renewed focus on wellbeing is necessary to protect the health and viability of our physician workforce,” says Ridout.

Sen also notes that the findings certainly can apply to other fields or lifestyle habits that might affect stress level on a regular and frequent basis.

“Research has implicated telomeres as an indicator of aging and disease risk, but these longitudinal findings advance the possibility that 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,” says Sen. “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 study is published in the journal Biological Psychiatry.

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