Washington: Sleep disorders are common among police officers in the US, a study has found.

The study, based on a survey of cops, indicated that about 40 percent have a sleep disorder, which was associated with an increased risk of adverse health, safety and even performance outcomes, an agency reported.

"Police officers frequently work extended shifts and long work weeks, which in other occupations are associated with increased risk of errors, unintended injuries, and motor vehicle crashes.

"It has been hypothesised that fatigue -- likely due to reduced duration and quality of sleep and untreated sleep disorders -- may play an important role in police officer unintentional injuries and fatalities.

"To date, the effect of sleep disorders on police officer health, safety, and performance has not been systematically investigated," Shantha MW Rajaratnam of Brigham and Women's Hospital in Boston, who led the study, said.

The study consisted of police officers participating in either an online or an on-site screening (n = 4,957) and monthly follow-up surveys (n = 3,545 officers) between July 2005 and December 2007.

A total of 3,693 officers in the United States and Canada participated in the online screening survey, and 1,264 officers from a municipal police department and a state police department participated in the on-site survey. The average age of the officers was 38.5 years.

Some 2,003 out of 4,957 participants (40.4 percent) screened positive for at least one sleep disorder. Of the total group, 1,666 (33.6 percent) screened positive for obstructive sleep apnea (OSA), the most common disorder, followed by 281 (6.5 percent) with moderate to severe insomnia; and 269 (5.4 percent) with shift work disorder (14.5 percent of those who worked the night shift).