More than 25 percent of over-the-road truck drivers suffer from obstructive sleep apnea, and those who forego treatment raise their risk of being a serious crash fivefold, according to a study by researchers at the University of Minnesota, Morris.

The results, released this week and published online in the journal Sleep, looked at more than 1,600 truckers diagnosed with obstructive sleep apnea (SA) and an equal number of commercial drivers who were screened and believed not to have the malady or did and followed their treatment plan.

"If we look at 1,000 truck drivers each working for a year, the drivers with obstructive sleep apnea who refuse mandated treatment would have 70 preventable serious truck crashes, compared to 14 crashes experienced by both a control group and by drivers with sleep apnea who adhered to treatment," said Stephen Burks, lead author of the study, and professor of economics and management at Morris.

Sleep apnea is a breathing-related sleep disorder that causes brief interruptions of breathing during sleep. In general, studies show that people with untreated sleep apnea have an increased risk of being involved in a fatigue-related motor vehicle crash.

Researchers with Morris' Truckers and Turnover Project gave drivers who have SA a mask with an air pump worn while sleeping to keep airways open. It was electronically monitored. The rates of preventable serious truck crashes per 100,000 miles driven were compared across the study groups.

In general, studies show that people with untreated sleep apnea have an increased risk of being involved in a fatigue-related motor vehicle crash. The Morris study found just how pronounced it is for truckers who don't follow treatment.

The findings come as the U.S. Department of Transportation opened a 90-day comment period earlier this month seeking input on a proposal of establishing rules requiring that bus drivers, truckers and railroad workers be tested for OSA.

A study conducted by the University of Pennsylvania and sponsored by the Federal Motor Carrier Safety Administration (FMCSA) and the American Transportation Research Institute of the American Trucking Associations found that almost one-third (28 percent) of commercial truck drivers have mild to severe sleep apnea.

"The paper's results suggest putting obstructive sleep apnea screening standards in the medical exam commercial truck drivers take every two years," Burk said.

For individuals with OSA, eight hours of sleep can be less refreshing than four hours of ordinary, uninterrupted sleep, according to a study by the American Academy of Sleep Medicine

Crash data from 2004 to 2013 show that sleepy commercial vehicle operators caused as many as 8,900 traffic deaths in the U.S. over that time period.

The study at Morris was supported by the Roadway Safety Institute at the University of Minnesota in the Twin Cities.