As many working people and students can attest, the sound of the alarm clock in the morning can mean an unpleasant jolt out of a nice deep sleep.
And disrupting the body’s internal clock in this way can lead to a higher risk of becoming overweight or obese, according to a new European study published in the journal Current Biology.
The study, led by Till Roenneberg at the University of Munich, evaluated the relationship between social jet lag — which the researchers describe as the discrepancy between one’s internal and social clocks — and body mass index.
Working from questionnaires completed by 6,500 central Europeans about their sleep habits, the researchers found that those who disrupted their biological rhythms, which are determined in part by genetics, had a greater chance of not only becoming overweight or obese but also more likely to smoke and drink more alcohol and caffeinated beverages.
“Our results demonstrate that living ‘against the clock’ may be a factor contributing to the epidemic of obesity,” the authors wrote.
Social jet lag, they explained, starts early in adolescence and continues throughout life until retirement. Early school times are not tuned in to the teenagers’ later natural wake times, and as people enter the work force, those who are night owls but have to wake up early also suffer the effects of insufficient sleep.
The circadian clock also plays a role in how the body burns energy, which “may contribute to weight-related pathologies,” wrote the authors.
Previous research, they continued, found that not getting enough sleep also increased the risk of obesity and metabolic disease, and shift workers were especially vulnerable.
“The situation, where people have to be active and try to sleep outside their circadian window, has been simulated in carefully controlled laboratory studies called forced desynchrony,” they explained. “These simulations result in an imbalanced glucose metabolism that normally is associated with metabolic syndrome or type 2 diabetes.”
Short sleep duration has also been linked to other health problems, including preclinical signs of Alzheimer’s disease and heart disease.
The majority of people start their work day before the end of that sleep window and fall asleep well after they feel tired, which the researchers believe is “of key importance in pending discussions on the implementation of daylight-saving time and on work or school times, which all contribute to the amount of social jet lag accrued by an individual,” the authors concluded.
ABC News’ Dr. Samantha Meaney contributed to this report.