New research suggests sleep apnea and excessive daytime sleepiness could significantly increase depression risk in men.

The findings, which were presented at the 2015 American Thoracic Society International Conference, were based on a community-based study of Australian men.

"An association between sleep apnea and depression has been noted in some earlier studies," said lead author Carol Lang, from the University of Adelaide, Australia. "Our study, in a large community-based sample of men, confirms a strong relationship even after adjustment for a number of other potential risk factors."

To make their findings, the researchers looked at 1,875 men between the ages of 35 and 83, who were tested for signs of depression twice over a five-year period. A random sample of 857 men without previously diagnosed severe obstructive sleep apnea (OSA) were assigned to undergo at home polysomnography and completed the Epworth Sleepiness Scale questionnaire.

After adjusting for outside factors, the researchers determined previously undiagnosed severe OSA is linked to an elevated risk of depression; excessive daytime sleepiness was also found to be associated with depression risk. Men who suffered from both conditions had between a 4 and 5 times higher risk of struggling with depression when compared to participants without either condition.

"Excessive daytime sleepiness and severe OSA were both associated with the prevalence and recent onset of depression in our community-based sample of men, and the presence of both was associated with an even greater risk," Lang said. "Men presenting with depression should be screened for OSA, so that an appropriate course of treatment can be planned."