Feeling tired? You’re not alone. A new study finds that many U.S. workers aren’t getting enough sleep, which is essential to optimal health, and that people who work multiple jobs are at heightened risk of getting less than the recommended hours of nightly rest.

To conduct the study, which was published in the December issue of the Sleep journal, researchers examined the responses of nearly 125,000 Americans ages 15 years old and older and who participated in the American Time Use Survey between 2003 and 2011. They found that work was the dominant reason for reporting less sleep across nearly all sociodemographic groups. Those who reported sleeping six hours or less (described in the study as “short sleepers”) also worked 1.55 hours more on weekdays and 1.86 hours more on weekends and holidays when compared to normal sleepers. (The American Academy of Sleep Medicine recommends that adults get about seven to nine hours of sleep per night for optimal health, productivity and daytime alertness.) Short sleepers also reported starting work earlier in the morning and working later into the evening. Adults who work multiple jobs were found to be 61 percent more likely to report sleeping six hours or less on weekdays.

In the study’s introduction, authors Mathias Basner, Andrea Spaeth and David Dinges highlight the importance of adequate sleep to health, noting that “sleep is a biological imperative,” with habitual short sleep associated with a variety of poor health outcomes, such as obesity, diabetes, hypertension, heart disease and all-cause mortality. In fact, sleep is so important to health that the Centers for Disease Control and Prevention increased its collection of information on sleep-related behaviors in recent years, stating that “insufficient sleep is an important public health concern.” The study also noted that adequate sleep is a core contributor to safety, pointing to the 83,000 traffic crashes that occur in the U.S. every year and that involve drowsy drivers. They write:

Despite the apparent benefits of sufficient sleep for cognitive performance, safety, and health, current representative surveys indicate that 35% to 40% of the adult US population report sleeping less than the usually recommended 7-8 hours on weekday nights, and about 15% report sleeping less than 6 hours. The high prevalence of habitual short sleep and its association with morbidity and mortality warrant the identification of populations at risk for habitual short sleep as well as the identification of behaviors that predispose to short sleep and that could be targeted in intervention programs.

Specifically, the study found that those 15- to 24- years-old are getting the most daily sleep when compared to older respondents. Those between the ages of 35 and 64 reported the least amount of daily sleep and were significantly more likely to be short sleepers. On average, black, Hispanic and Asian respondents slept longer than white respondents. However, black respondents were also more likely to be short sleepers than white respondents. On average, those with a college degree experienced significantly less sleep than those with a high school degree; however, those with higher educational attainment also experienced fewer changes in sleep patterns than high school graduates. Full-time high school students got significantly less sleep during weekdays when compared to private-sector workers, but got more sleep on the weekends and holidays. People working multiple jobs got significantly less sleep, were more likely to be short sleepers, and less likely to be long sleepers on weekends and holidays.

Overall, short sleepers worked more hours, starting working earlier and continued working later into the day. The study stated: “Working ranked as the primary waking activity that was performed instead of sleep across all sociodemographic strata, with the exception of respondents retired, unemployed, or otherwise not in the labor force.” So, what’s an appropriate intervention — how do we find a good balance between work and the health-protective benefits of sleep? The study authors offered a number of possible answers, such as making work start times more flexible, reducing the prevalence of multiple jobs and finding ways to reduce commuting times (for example, more reliable public transit could be one way to help workers get more sleep).

In accompanying editorial published in the same issue of Sleep, author Lauren Hale, an associate professor in the Program in Public Health at Stony Brook University, described the study as “another opportunity to raise concerns about sleep patterns as both an unmet public health and a social justice problem.” Citing the study’s findings that those with lower levels of social status are more likely to sleep too little or too much — both of which are associated with negative health issues — she wrote that the distribution of adequate sleep tends to favor the more advantaged.

“We must respect the reality that many time-use allocation decisions are not factors over which people have total control, due to both structural and psychological barriers,” Hale writes. “While it is tempting to attribute sleep duration and timing patterns to active choices that can be altered through well-meaning targeted interventions, we must think deeply about the underlying structural and psychological factors that determine sleep patterns.”

Visit the American Academy of Sleep Medicine newsroom to read more and request a full copy of the study.

Kim Krisberg is a freelance public health writer living in Austin, Texas, and has been writing about public health for more than a decade.