People who have trouble sleeping tend to have less volume in certain regions of the brain than those without sleep problems, a new study of Persian Gulf War veterans suggests.
"People discount the importance of sleep. So many things seem so much more important than a few extra hours of sleep a night," said lead author Linda L. Chao. "The study suggests we shouldn't discount sleep importance."
Chao, from the University of California, San Francisco, collaborated with researchers at the Department of Veterans Affairs Medical Center in San Francisco on the study published in the journal Sleep.
Previous research has linked sleep disturbances to structural brain changes, the authors note. In their study, sleep was associated with the amount of gray matter in the brain's frontal lobe in particular.
"There's other corroborating data showing that insomnia and a variety of psychiatric illnesses are reflected in reduced volumes in the brain, which makes sense because sleep and mood are functions of the brain," said Dr. John Winkelman.
A psychiatrist, Winkelman is chief of the sleep disorders clinical research program at Massachusetts General Hospital in Boston. He was not involved in the current study.
He described the frontal lobes as "an essential part of human functioning," necessary for planning, strategizing, mood and affect.
Veterans with post-traumatic stress disorder (PTSD) frequently complain about sleep difficulties, according to Chao and her colleagues. Studies have found high rates of sleep disorders among veterans of America's wars in
Iraq and
Afghanistan who had head injuries or PTSD.
For the current study, the researchers scanned the brains of 144 mostly male veterans using magnetic resonance imaging (MRI).
They measured sleep quality with the Pittsburgh Sleep Quality Index, a crude, self-rated index that asks broad questions about sleep patterns over the past month.
For example, the index asks participants a single question about the time they usually went to bed over the past month and another about how long it usually took them to fall asleep.
The researchers found participants who reported poor quality sleep overall had less frontal lobe gray matter than vets who reported sleeping relatively well.
In addition to sleep troubles, a host of psychological problems plagued the study veterans. Half had abused alcohol, 40 percent had had major depressive disorder at some point and 18 percent had PTSD.
Still, the link between sleep troubles and brain volume held even after the researchers took those problems and psychotropic medicine use into account.
Winkelman cautioned against inferring a cause-and-effect relationship between sleep and brain volume or generalizing the results of a study on veterans with a range of psychiatric problems to the general population.
But Chao believes the findings could apply to anyone, not just war veterans.
Although she stressed that the study underscores the importance of a good night's sleep, she agreed that it's not possible to say that troubled sleep causes a decrease in frontal lobe gray matter, or vice versa.
"We only know there's a relationship," said Michael Breus, an Arizona clinical psychologist who is board-certified in sleep disorders. "We don't know which came first."
Breus was not involved in the current study. He applauded the researchers for examining sleep patterns in war veterans, a group particularly plagued with disturbed sleep.
"If they've been in an active theater of war, they haven't slept well since they've been in an active war," he said.
He said polysomnography, which monitors people's sleep and collects objective data, would have made the results of the current study more meaningful.
Chao also said she would have preferred to use objective sleep data. But the current report was based on a second look at data from a prior study.
"The data says to us this could be a very interesting population to learn more about," Breus said. "If we can learn more about veteran sleep, we can help them sleep more."