That's the conclusion of a University of Michigan study presented April 17 at the annual meeting of the Population Association of America.
The study analyzes two nationally representative surveys of approximately 2,300 U.S. adults that monitored the same workers for up to a decade. Over that time, roughly half the respondents said they had trouble sleeping.
"Together, work and sleep take up about two-thirds of every weekday," said U-M sociologist Sarah Burgard. "But until now, very little research has focused on the connections between work and sleep for the average U.S. worker."
Previous research has shown that lack of sleep can have serious consequences ranging from traffic accidents to health problems, chronic disease and mortality. As many as 70 million Americans suffer from some kind of chronic sleep disorder.
But this is the first U.S. study to clarify the link between work and sleep quality for all workers, not just rotating shift workers or medical students, who have unusual work and sleep arrangements.
Because the surveys were prospective?following the same people over time?the researchers were able to show that work conditions affected sleep patterns, not the other way around. Their analysis controlled for initial sleep quality, health, pessimism and other confounding factors.
Respondents who felt upset or bothered at work on a frequent basis, or had on-going personal conflicts with bosses or co-workers, were about 1.7 times more likely than others to develop sleep problems.
"Massive changes over the past half-century have reshaped the workplace, with major implications for sleep," Burgard said. "For many workers, psychological stress has replaced physical hazards.
"Physical strain at work tends to create physical fatigue and leads to restorative sleep, but psychological strain has the opposite effect, making it more difficult for people to sleep."
Burgard and graduate student Jennifer Ailshire also explored how work-family conflict, gender, education and job status affected the relationship between work and sleep.
As women have entered the labor force in large numbers, dual-earner households and single-parent families have made the time-crunch a major factor, Burgard said.
As expected, Burgard and Ailshire found that work-family conflicts and the presence of children under the age of three were significant predictors of negative changes in sleep quality. Respondents with children under the age of three were about 2.2 times as likely to report poor sleep quality, but having young children did not explain the association between hassles at work and sleep quality.
Surprisingly, however, they found no evidence that long hours, or working nights or weekends?strategies often adopted by working parents to juggle childcare and jobs while minimizing the use of baby-sitters or daycare facilities?had a negative impact on reported sleep quality.
In future research, Burgard plans to explore factors that could buffer workers from negative working conditions, such as age and a sense that one's job is useful or helpful to others. She also plans to examine interventions that could break the link between work conditions and troubled sleep.
Burgard is assistant professor of sociology at the U-M College of Literature, Science, and the Arts; assistant professor of epidemiology at the U-M School of Public Health; and assistant research scientist at the U-M Institute for Social Research (ISR).
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