About 40 percent of police officers in the United States and Canada suffer from sleep problems that may harm their ability to function on the job, said a U.S. study published on Tuesday. Of nearly 5,000 police officers who took part in an online survey, 40 percent had at least one sleep disorder, most commonly obstructive sleep apnea, followed by insomnia and shift work disorder. Those who had sleeping problems were more likely to report feelings of depression, burnout, and dozing at the wheel than those who slept well. Poor sleepers also showed higher rates of diabetes, heart disease and caffeine intake. The study, led by Shantha Rajaratnam of Brigham and Women's Hospital in Boston, Massachusetts, appears in the Journal of the American Medical Association. While excessive sleepiness was reported by nearly 29 percent of participants, even more admitted to having fallen asleep while driving (46 percent) and 57 percent said it happened at least once or twice per month. Fourteen percent said they dozed while driving at least once or twice in a single week. Sleepy cops were also more likely to take out their frustrations on the public. Police who screened positive for sleep disorders “were more likely to report ... making errors or committing safety violations due to fatigue; having uncontrolled anger toward a citizen or suspect; incurring citizen complaints; having absenteeism; or falling asleep during meetings,” the study said. The study included sworn police officers at the local and state levels. Most were in the United States (97 percent), while three percent were in Canada. Since the survey was described as the first attempt to systematically assess sleep disorders in police and their effects on performance, the researchers called for more investigation into how sleep problems could be avoided. “A large proportion of police officers in our sample showed a positive sleep disorder screening result, which was associated with adverse health, safety, and performance outcomes,” the study said. “Further research is needed to determine whether sleep disorder prevention, screening, and treatment programs in occupational settings will reduce these risks.” Sleep disorders affect 50-70 million Americans, but often go undiagnosed and untreated, the study said.