Although it remains unclear how the conditions are linked, Maurice Ohayon, MD, PhD, said his study should encourage physicians to test depressed patients for this type of sleep disorder.
"Physicians who see people with depression shouldn't stop at the first diagnosis, but instead look into the presence of a breathing-related sleep disorder," said Ohayon, an associate professor of psychiatry and behavioral sciences. His study appears in the current issue of the Journal of Clinical Psychiatry.
These disorders include such breathing anomalies as chronic, disruptive snoring and obstructive sleep apnea syndrome, a disorder in which people stop breathing for brief periods up to hundreds of times a night. Left untreated, the disorders can lead to hypertension, stroke and cognitive deterioration. They can also affect a person's daily routine and disrupt his or her familial, social and professional life.
"This type of disorder increases a person's chances of feeling sleepy and irritable, having a dispute with a family member or colleague, or getting into a traffic accident," said Ohayon.
Several studies have suggested that sleep apnea is associated with a higher rate of depressive disorder and that treating sleep apnea could help control depression in patients. But no previous study had explored this association and its risk factors in the general population.
To assess the impact of the two disorders in the general population, Ohayon conducted a telephone survey with adults in five countries (the United Kingdom, Germany, Italy, Portugal and Spain). More than 18,000 people were chosen as a representative sample of 206 million Europeans. The participants answered questions pertaining to sleep quality and schedules, breathing-related sleep disorders, mental disorders and medical conditions.
After analyzing the data, Ohayon found that 2.1 percent of the people surveyed had sleep apnea - a figure consistent with data from past studies on selected populations - and 2.5 percent had another type of breathing-related sleep disorder. Eighteen percent of respondents who were experiencing a depressive disorder (4 percent of all respondents) also had a breathing-related sleep disorder, compared with 3.8 percent of non-depressed respondents. That represents a five-times increased likelihood of breathing-related sleep disorders among depressed people.
"This is the first study to show the strength of the link between the two disorders," said Ohayon, adding that even after controlling for obesity and hypertension (important factors in each disorder) the association remained strong.
It remains unclear whether depression occurred before or after sleep apnea, and to what extent sleep apnea contributes to the maintenance or aggravation of depression. Ohayon said the link between treating sleep apnea syndrome and the evolution of depressive disorders needs further investigation. He hopes physicians will consider the association between the disorders and depression when treating depressed patients. "Once people have their sleep apnea recognized, there is a lot we can do to help them," he said.
Ohayon received funding for his research from the Medical Research Council of Quebec and an unrestricted educational grant from the Sanofi-Synthelabo Group, a pharmaceutical company.
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