BEIJING, Sept. 2 (Xinhuanet) -- Insomnia costs average U.S. worker 11.3 days, or 2,280 dollars, in lost productivity each year, according to a new study published in journal Sleep.

The total cost to the nation is 63.2 billion dollars annually, the study said.

Researchers analyzed information about sleep habits and work performance from 7,428 workers taking part in Harvard Medical School's American Insomnia study survey in 2008-09.

As a result, 23.2 percent of the participants suffered insomnia, characterized by a hard time falling or staying asleep.

Moreover, insomnia rates were 19.9 percent for those with less than a high school education and 21.5 percent for college graduates.

"We were shocked by the enormous impact insomnia has on the average person's life," said Ronald C. Kessler, a lead author and a psychiatric epidemiologist at Harvard Medical School.

"It's an underappreciated problem. Americans are not missing work because of insomnia. They are still going to their jobs but accomplishing less because they're tired," Kessler noted.

Employers usually ignore the consequences of insomnia because it's not considered an illness resulting in workers' absenteeism.

But the high cost of lost sleep identified in this study indicates that employers need to take it more seriously.