Bleary-eyed shift workers have had their suspicions confirmed. A new study has found working as many as one-in-four night-shift workers develop sleep disorders.

Focusing on the Detroit area, the U.S. Department of Labour says there are 400,000 night-shift workers in the region. And, the Henry Ford Hospital's Sleep Disorders and Research Center estimates as many as 100,000 of them have trouble sleeping.

According to a staff physician and senior research scientist at the Center, Gary Richardson, the problem appears unavoidable for those who work the odd hours.

"We are fundamentally, biologically day animals. And it's always going to be a struggle to work at night," he told The Detroit News on Sunday.

Research shows that people suffering from so-called shift work sleep disorder are more likely to suffer other health effects, from colds to heart disease to weight gain.

Previous studies have also shown that people suffering from just short-term bouts of sleep deprivation suffer from lower glucose tolerance as well as elevated blood pressure and stress hormone levels.

Employees with sleep disorders are also twice as likely to suffer accidents on the job.

In Canada, surveys peg the typical night's sleep at six hours -- or two hours short of the recommended average rest.