The American Academy of Sleep Medicine has an article in the December issue of Sleep looking at how people who sleep less spend their extra waking time. Roughly “30 percent of employed U.S. adults typically sleep 6 hours or less in a 24-hour period.” So what do these people do instead?

The study finds that “paid work time is the primary waking activity exchanged for sleep and suggests that chronic sleep loss potentially could be prevented by strategies that make work start times more flexible.”

The study draws on the American Time Use Survey, and includes data from almost 125,000 people surveyed between 2003 and 2011.

Results show that work is the dominant activity exchanged for less sleep across practically all sociodemographic categories. Compared to normal sleepers, short sleepers who reported sleeping 6 hours or less worked 1.55 more hours on weekdays and 1.86 more hours on weekends or holidays, and they started working earlier in the morning and stopped working later at night. The highest odds of being a short sleeper were found among adults working multiple jobs, who were 61 percent more likely than others to report sleeping 6 hours or less on weekdays. Respondents who were unemployed, retired or absent from the labor force also obtained significantly more sleep and were less likely to be short sleepers.

“The evidence that time spent working was the most prominent sleep thief was overwhelming,” said lead author Dr. Mathias Basner, assistant professor of sleep and chronobiology in psychiatry at the University of Pennsylvania Perelman School of Medicine in Philadelphia.

Short sleepers also traveled more, started traveling earlier in the morning, and stopped later in the evening than normal sleepers. The travel pattern, with peaks at 7 a.m. and 5 p.m., strongly suggests that the majority of travel time is associated with commuting.