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The study focused on adults 65 and older, and poor sleep included difficulty falling or staying asleep, waking up early in the morning, experiencing daytime sleepiness and not feeling fully rested after a night's sleep.
"These findings suggest that sleep disturbances stand alone as a valid risk factor -- independent of depressed mood -- and worthy of focus as a potential [suicide] risk factor, screening and intervention tool," said lead researcher Rebecca Bernert, an instructor of psychiatry at Stanford University School of Medicine. "Compared to many other known suicide risk factors, sleep disturbances are arguably less stigmatizing and may be undone, and are highly treatable."
Among the 20 study participants who died by suicide, 19 were men. The researchers randomly matched these 20 people to 400 living participants based on shared age, sex and location, and then compared their sleep quality and depression scores.
The study couldn't prove that sleeping problems cause suicidal thoughts or attempts, nor could it explain why the link may exist. But, Bernert said, it's likely that poor sleep affects the ability to regulate moods.
"The idea is simple: when we sleep poorly, it impacts how we feel and the way in which we manage our emotions, as well as decision-making," Bernert said. Past research has shown that fragmented sleep can result in more intense negative emotions, impaired judgment and difficulty managing fear or anger.
Those who reported having poor sleep quality at the start of the study had 40 percent greater odds of dying by suicide during the next 10 years before depression symptoms had been considered. Even after making calculations to remove the effects of depression symptoms, the odds of dying by suicide were 30 percent higher for those reporting poorer sleep quality, the study authors said.
Also, those who reported not feeling well-rested after sleeping had twice the odds of dying by suicide compared to those not reporting sleeping problems, even after symptoms of depression had been considered. And sleep disturbances better predicted who died by suicide over a decade than depression symptoms did, the study authors reported in the Aug. 13 online edition of JAMA Psychiatry.
The researchers used two separate questionnaires, one on sleep quality and one on depression symptoms, for their calculations.
Yet William Kohler, medical director of the Florida Sleep Institute in Spring Hill, Fla., said he's skeptical about how well the researchers could completely account for depression symptoms since they are so similar to the symptoms of poor sleep.
"We have to ask what's the cart and what's the horse because it's not common to be really sleep-deprived and then be wide-eyed and bushy-tailed and positive about things," Kohler said.
"We know that sleep disturbance causes depressive symptoms, such as lack of energy, lack of interest in things one enjoys and feeling a little down the next day, so I'm not sure how they would separate that out," he added.
Separating them out is what the researchers said they attempted to do.
"Sleep disturbances and suicidal ideation are both symptoms -- among a constellation of symptoms -- of depression, which is why it is crucial to disentangle them as risk factors and the way in which they may interact to increase risk," Bernert said. "It is important to note that suicide is the tragic outcome of multiple, often interacting risk factors and medical conditions."
Approximately 12 out of every 100,000 people die by suicide each year in the United States. Individuals thinking about suicide can reach a nearby certified crisis center by calling the National Suicide Prevention Lifeline at 1-800-273-TALK.
The U.S. Substance Abuse and Mental Health Services Administration ranks sleep difficulties as one of the top 10 warning signs of suicide. Past studies have linked insomnia, nightmares and overall poor sleep quality to an increased risk of suicidal thoughts and attempted suicide. But those studies did not usually control for depression.
This new study differs from past research because of its size, length and focus on older Americans. The researchers tracked more than 14,000 adults, aged 65 and older, for 10 years. The adults assessed their sleep quality and depression symptoms six times during that decade.
Bernert said she and her colleagues are now investigating why the link between poor sleep and suicide might exist.
The U.S. Centers for Disease Control and Prevention and the U.S. National Institutes of Health contributed funding for the study.
Copyright © 2014 HealthDay. All rights reserved.
SOURCES: Rebecca Bernert, Ph.D., instructor, psychiatry, Stanford University School of Medicine, Stanford, Calif.; William Kohler, M.D., medical director, Florida Sleep Institute, Spring Hill, Fla.; Aug. 13, 2014, JAMA Psychiatry, online