People with depression or other mental illnesses often report trouble sleeping, daytime drowsiness and other sleep-related issues. Now a growing body of research is showing that treating sleep problems can dramatically improve psychiatric symptoms in many patients.

Much of the latest work illustrates how sleep apnea, a common chronic condition in which a person repeatedly stops breathing during sleep, may cause or aggravate psychiatric symptoms. In past years sleep apnea has been linked to depression in small studies and limited populations. Now a study by the Centers for Disease Control and Prevention strengthens that connection. The CDC analyzed the medical records of nearly 10,000 American adults with sleep apnea. Men diagnosed with this disorder had twice the risk of depression—and women five times the risk—compared with those without sleep apnea. Writing in the April issue of Sleep, lead author Anne G. Wheaton and her colleagues speculate that in addition to interrupting sleep, the oxygen deprivation induced by sleep apnea could harm cells and disrupt normal brain functioning.

Treating this disorder shows promise for reducing symptoms of depression, a recent study at the Cleveland Clinic suggests. In the experiment, patients went to bed wearing a mask hooked up to a machine that increases air pressure in their throat. The increased pressure prevents the airway from collapsing, which is what causes breathing to cease in most cases of this disorder. Using this machine, psychiatrist Charles Bae and his colleagues treated 779 patients who had been diagnosed with sleep apnea. After an average of 90 days of sleeping with the machine, all the patients scored lower on a common depression survey than before the treatment—regardless of whether they had a prior diagnosis of depression or were taking an antidepressant. The data were presented in June at the SLEEP 2012 conference in Boston.

Investigating their patients' sleep health might allow doctors to alleviate mental disturbances early—perhaps even before patients try psychiatric drugs. This treatment could be especially important for children, according to three new studies that show sleep is associated with mental disturbance at young ages. An August study in Medical Hypotheses reported that about 25 to 50 percent of children and adolescents with attention-deficit hyperactivity disorder experience sleep problems. A few months earlier in the journal Pediatrics, researchers found that of the 11,000 children in the study, those with disordered breathing in sleep (as reported by their parents) had 40 percent more behavioral difficulties at four years old and 60 percent more at age seven. Sleep disturbances affect moods, too—and not simply by producing crankiness. Adolescents who reported daytime drowsiness were also more likely to experience sadness, according to a March study in the Journal of Mental Health Policy and Economics.

Steven Y. Park, assistant professor of otolaryngology at the Albert Einstein College of Medicine, has long been advocating that sleep disorders are an underlying cause of many psychiatric disorders. “The way I see it,” Park says, “you can't consider a psychiatric disorder without thinking about a sleep-breathing problem.”