Did you have a long sleep-in last weekend?
If you did, you may be among the estimated two-thirds of Americans who regularly experience “social jetlag” — a shift in their weekend sleep schedule to one that is more aligned with their body’s natural, circadian rhythms.
For most Americans, that shift means waking up later than they do on weekdays.
Social jetlag is difficult to avoid in today’s 9 to 5 (or 8 to 6?) working world. But, unfortunately, there is mounting evidence that it is bad for our health.
The latest piece of evidence comes from a study published last week in the Journal of Clinical Endocrinology & Metabolism. In that study, researchers from the University of Pittsburgh found a strong association between social jetlag and an increased risk of metabolic changes in the body that can contribute to obesity, type 2 diabetes and heart disease.
Scientists have long known that shift workers are at greater risk than normal daytime workers of developing chronic diseases such as diabetes and heart disease. This new study is the first one, say its authors, to show quantitatively that social jetlag — which essentially involves traveling back and forth each week between two time zones — can also lead to unhealthy metabolic changes linked to those diseases.
For the study, the researchers studied data collected from 445 healthy men and women aged 50 to 54. Each worked for at least 25 hours a week outside the home, but not as a shift worker.
The participants wore devices on their wrists that tracked their movement and sleep for 24 hours a day for a week. They also filled out questionnaires about their diet and health habits. Blood samples were collected to measure various health-related biomarkers, such as cholesterol and blood glucose levels.
The data revealed that about 85 percent of the participants went to sleep later and woke up later on their “free” days than on their workdays. The other 15 percent did the opposite: They got up earlier on their non-working days.
A further crunching of the data revealed that the participants with the greatest differences between their working- and non-working-day sleep schedules tended to have poorer cholesterol profiles, higher fasting insulin levels, and more resistance to insulin than the participants with less social jetlag. They also had larger waist circumferences and higher body mass indexes.
Those factors are all associated with an increased risk of type 2 diabetes and heart disease.
The findings held even after the researchers adjusted for health behaviors, such as physical activity, calorie intake and alcohol consumption, and for how long people slept.
Limitations and implications
This study does not prove that having mismatched sleep schedules on working and non-working days contributes to diabetes or heart disease. It just found an association between social jetlag and markers for those illnesses. Other factors — ones not identified in this study and having nothing to do with social jetlag — may also explain the results.
Furthermore, the study’s findings do not mean that sleeping in on the weekends is bad for you.
What it does suggest, however, is that societal imposed work schedules that are not in sync with our natural, circadian rhythms may be harmful to our health.
“If future studies replicate what we found here, then we may need to consider as a society how modern work and social obligations are affecting our sleep and health,” said Patricia Wong, a graduate student at the University of Pittsburgh and the study’s lead author, in a released statement. “There could be benefits to clinical interventions focused on circadian disturbances, workplace education to help employees and their families make informed decisions about structuring their schedules, and policies to encourage employers to consider these issues.”
You’ll can read the study in full at the Journal of Clinical Endocrinology & Metabolism website.