Is "disturbed sleep a cause of serious mental illness, or simply an
antecedent to it?"
"My answer is yes!" said ruth Benca, M.D., Ph.D., a professor
of psychiatry at the University of Wisconsin School of Medicine.
Despite her jest, Benca and others weighed evidence supporting links
between troubled sleep and troubled minds at the annual meeting of the
Associated Professional Sleep Societies in Salt Lake City, Utah, in June.
Since diagnostic criteria for primary insomnia and major depressive
disorder overlap, it often is hard to tell in clinical settings where a sleep
disorder ends and depression begins, said Benca, a past president of the Sleep
research Society. Nonetheless, people with major depression generally report
more severe depression and more highly disturbed sleep than do people with
Sleep disturbance is the most common refractory symptom in treated major
depressive disorder, she said. Fatigue ranks second. Sleep disturbance also is
the first symptom to appear in recurrence. These findings, Benca said, suggest
sleep disruption is a core symptom in mood disorders.
More than 50 published epidemiological studies of insomnia using data
collected from representative community-dwelling samples or populations
consistently show an association between insomnia and major depressive
episodes, noted Maurice Ohayon, M.D., D.Sc., Ph.D., director of the Sleep
Epidemiology Research Center at Stanford University School of Medicine.
Longitudinal studies show that people who report insomnia at a first
evaluation are more likely than people without insomnia to have depression at
their next evaluation, Ohayon said. People with insomnia at two separate
evaluations have a higher risk of depression than those without persistent
In a cross-sectional and retrospective study of a community-based sample of
722 adults aged 20 to 89, Daniel Taylor, Ph.D., an assistant professor of
psychology at the University of North Texas in Denton, and colleagues found
that people with insomnia were 9.82 times and 17.35 times more likely to have
clinically significant depression and anxiety, respectively, than people
without insomnia. The researchers excluded people with other sleep or medical
disorders from their study.
About 20 percent of people with insomnia had clinically significant
depression, and 19.3 percent had clinically significant anxiety, the
researchers reported in the November 2005 Sleep.
The relationship between insomnia and depression and anxiety likely is
reciprocal in some cases, Taylor said. A diathesis-stress model may trigger
these associations, he suggested. People who develop insomnia at times of
stress may find that lying in bed awake in the dark intensifies feelings of
failure or worries about the future.
"If we can rapidly address their insomnia," Taylor said,"
maybe we can bring them down to a subthreshold state."
Research now under way aims to see whether cognitive-behavioral therapy for
insomnia lowers the risk of depression, said Daniel Kripke, M.D., a professor
of psychiatry emeritus at the University of California at San Diego. Some
hypnotic medications may boost the risk of depression as compared with
placebo, he said. He examined manufacturers' prescribing information for four
recently approved hypnotics, finding depression reported as an adverse event
in 109 of 5,535 subjects who took the medication, and in 21 of 2,318 who took
the placebo, a roughly twofold increased risk (unpublished data).
While even clinicians sometimes quip, "Insomnia doesn't kill,"
insomnia is far from trivial, said Douglas Moul, M.D., M.P.H., an assistant
professor of psychiatry at the University of Pittsburgh School of Medicine. He
cited a man who developed trouble sleeping and depression after his brother
died. Six months later, the man committed suicide. While in treatment for his
depression, the man frequently told his physician, "All I need is for my
sleep to be right."
One can imagine an underlying genetic risk in this individual, modified by
exposure to life events, with pathology building up over time, Moul said, and
worsened by the brother's death.
Studies of circadian rhythms support a causal role for insomnia in
depression, said Fred Turek, Ph.D., a professor of neurobiology and physiology
and director of the Center for Circadian Biology and Medicine at Northwestern
Some people with depression experience early morning awakening, he noted.
This phenomenon is hypothesized to represent an advance of the body's
sleep/wake cycle and cortisol rhythms, he said, and suggests that disordered
circadian time-keeping may contribute to depression.
A genetic animal model for depression, the Wistar-Kyoto rat, exhibits sleep
fragmentation and sleep-wake cycle disturbances similar to those in people
with depression, he said.
"No one would say insomnia causes all major depression," he
said, "but it may have that effect in some people. We have to think
about whether temporal disorganization in the brain is playing a contributory
role in these individuals and figure out how to identify them and treat
Most psychiatrists have been trained to treat a primary disorder, with the
expectation that accompanying insomnia will improve, too, said Benca, who
reviewed the diagnosis and treatment of persistent insomnia in the March 2005
Recent findings, she said, "imply that we should treat insomnia from
the get-go—that along with depressive symptoms, insomnia should be a
primary target of treatment."
Treatment of insomnia today is akin to that of pain in years past, she
said, asserting, "Sleep problems deserve the same attention as other