Patients with a sleep-related breathing disorder may be significantly more likely to develop depression, with the risk for depression increasing with the severity of the breathing disorder, according to a study in the September 18 issue of Archives of Internal Medicine.

Hypopnea and apnea during the night are hallmarks sign of sleep-related breathing disorder, according to background information in the article. The disorder has been linked to a variety of negative health consequences including cardiovascular disease and difficulty functioning during the day.

Previous studies have suggested that depression improves when sleep-related breathing disorder is treated, indicating a relationship between the two common conditions. Characterizing the relationship, the authors wrote, could “guide screening for depressive symptoms in patient populations with sleep-related breathing disorder, suggest strategies for managing sleep-related breathing disorder?related depression and alert clinicians about the possibility of untreated depression complicating adherence to sleep-related breathing disorder mitigation strategies and treatments ....”

Paul E. Peppard, PhD, and colleagues at the University of Wisconsin?Madison evaluated 1,408 adults (788 men, 620 women) between the ages of 30 and 60 years at the beginning of the study in 1988. Participants stayed overnight in a laboratory once every four years, during which time sleep was monitored with 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.

During the 3,202 sleep studies, 334 showed no evidence of hypopnea or apnea. Among cases of sleep-related breathing disorder, 1,911 were categorized as minimal, defined as an average of fewer than 5 episodes of reduced or paused breathing per hour; 606 were mild, with an average of 5 to 14 such events per hour; and 351 were moderate or worse, with 15 or more events per hour.

About twice as many men as women had mild, moderate or severe sleep-related breathing disorder - 14 percent of sleep studies among men revealed moderate sleep-related breathing disorder versus 6 percent of women. Throughout the study, there were 649 cases of mild depression and 392 of moderate or more severe depression. Women were about twice as likely to be depressed as men (27 percent versus 15 percent).

Compared with patients without sleep-related breathing disorder, those with minimal disease 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. “Among these studies, an increase in sleep-related breathing disorder to the next higher category (for instance, from no sleep-related breathing disorder to minimal sleep-related breathing disorder) was associated with a 1.8-fold increased odds for development of depression compared with unchanging sleep-related breathing disorder,” the authors wrote.

“For example, persons initially without sleep-related breathing disorder but in whom minimal sleep-related breathing disorder developed during a four-year period are estimated to be at 80 percent greater odds for development of depression than those who remain without sleep-related breathing disorder.”

“Our longitudinal findings of a dose-response association between sleep-related breathing disorder and depression provide evidence consistent with a causal link between these conditions and should heighten clinical suspicion of depression in those with sleep-related breathing disorder,” they concluded.