(Health.com) -- People with sleep apnea, a breathing disorder that causes frequent sleep disturbances, often feel tired and unfocused during the day. But that may not be the only fallout: New research suggests the disorder also dramatically increases the risk of depression.
Researchers at the Centers for Disease Control and Prevention (CDC) found that men with diagnosed sleep apnea are more than twice as likely as other men to exhibit signs of clinical depression, such as feeling hopeless and uninterested in everyday activities. The picture was even worse among women: A sleep apnea diagnosis increased the risk of depression symptoms fivefold.
What's more, the study suggests that sleep apnea is underdiagnosed. More than 80% of the people who reported classic symptoms such as snorting or gasping for breath on most nights of the week had never received an official diagnosis. This group, too, had a threefold higher risk of depression compared to people who had no trouble breathing at night.
"We're underdiagnosing this problem," says Carl Boethel, M.D., a sleep specialist at the Texas A&M Health Science Center College of Medicine, in Temple, who was not involved in the study. "Physicians in the sleep community and in the psychiatric community need to do a better job of screening and getting effective treatment."
Sleep apnea and related problems occur when the airway becomes blocked during sleep, restricting breathing. The disorder can be caused by several factors, including oversized tonsils, the structure of a person's airway, or excess fat surrounding the windpipe. Sleep apnea is closely associated with obesity, a fact the researchers took into account by controlling for body mass index in their analysis.
The study, which appears in the April issue of the journal SLEEP, is the first of its kind to look at a representative cross-section of the U.S. population. The data was drawn from the National Health and Nutrition Examination Survey (NHANES), an annual survey conducted by the CDC.
Six percent of men and 3% of women had received a sleep apnea diagnosis, the survey found, while 7% of men and 4% of women reported breathing problems on at least five nights per week.
Depression was assessed using a standard questionnaire that asked how often during the past two weeks the participants had "little interest or pleasure in doing things" or felt "down, depressed or hopeless," for instance. Five percent of men and 8% of women had scores indicating "probable" depression, according to the researchers.
A complicating factor is that the effects of depression and sleep apnea can be difficult to distinguish, says psychiatrist Michael Weissberg, M.D., co-director of the insomnia and sleep disorders clinic at the University of Colorado School of Medicine, in Denver.
"There probably is an important connection between depression and sleep apnea, but it's hard to sort out who has what," Weissberg says.
"Sleep disruption, particularly insomnia, can be a risk factor for developing depression, and a lot of symptoms of people who have sleep apnea -- they feel lousy, they can't think straight -- are similar to symptoms people have in depression."
The study shows only an association, not cause and effect, and the researchers can't rule out the possibility that an unidentified factor could contribute to both sleep apnea and depression. But it's plausible to think that sleep apnea could directly cause depression.
The sleep interruptions that characterize the disorder have been shown in previous research to affect mood. And on a cellular level, the momentary drop in oxygen that occurs when a sleeping person stops breathing could lead to brain changes by triggering stress or inflammation, says Anne Wheaton, Ph.D., the lead author of the study and an epidemiologist in the CDC's division of population health.
"Interrupted sleep may be associated with problems as far as what's going on in the brain," Wheaton says. "You need that steady sleep."
There was some good news in the study: Snoring, which sometimes accompanies sleep apnea, did not appear to be associated with depression.
The 37% of men and 22% of women who reported snoring at least five nights per week were no more likely to be depressed than those who never snored.
Copyright Health Magazine 2011