Individuals who have sleep-related breathing disorder appear significantly more likely to develop depression, with odds of depression increasing as breathing disorders becomes more severe, according to a study in the September 18 issue of Archives of Internal Medicine, a theme issue on sleep.

Paul E. Peppard, PhD, and colleagues at the University of Wisconsin–Madison evaluated 1,408 adults (788 men, 620 women) who were between the ages of 30 and 60 at the beginning of the study, in 1988. The participants stayed overnight in a laboratory once every four years, during which time sleep was monitored with a test known as polysomnography and breathing disturbances were recorded. By May 2005, 449 participants had completed one sleep study, 382 completed two, 319 completed three and 258 completed four, for a total of 3,202 sleep studies. At each sleep study, body mass index was recorded and interviews and questionnaires completed by participants provided information about medical history, lifestyle habits, demographics and whether they had difficulty sleeping at night (insomnia) or felt sleepy during the day.

Compared with patients without sleep-related breathing disorder, those with minimal cases of the condition were 1.6 times as likely to be depressed; those with mild cases, twice as likely; and those with moderate or worse, 2.6 times as likely. Individuals whose breathing problems worsened over time increased their risk for depression.