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For some adults, insomnia may be caused by a fear of the dark, finds a new study by researchers at Ryerson University in Toronto.

In the study of 93 students, nearly half acknowledged being afraid of the dark, and they were more likely to poor sleepers than good ones. “We never thought we would see this,” says Dr. Colleen Carney, assistant professor of psychology at Ryerson University. “We didn’t think people would admit or acknowledge this fear. They would say it’s for kids, or be too embarrassed.”

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The participants filled out questionnaires on their sleep behavior, whether or not they had been afraid of the dark as children and they were still afraid of the dark. They also completed an insomnia assessment; based on their responses, the researchers divided the participants into two groups: good and poor sleepers.

Following the questionnaires, the participants confirmed the participants’ fear of the dark by putting them in either a dark or lit lab room and subjecting them to unexpected bursts of white noise. The researchers measured the students’ blinking patterns, paying close attention to how they changed in response to the noises. “If you’re already a little anxious, the noise will make you flinch. We looked at eye reactions because it is one of the most robust ways to measure this anxiety. If you blink immediately after the noise, that means it startles you,” says Carney.

The researchers found that when the lights went out, the poor sleepers were more easily startled than the good sleepers. The poor sleepers became increasingly anxious during their time spent in the dark, while the good sleepers responded less and less to the noises and appeared to get used to them. There was no difference between the groups’ reactions in the light.”People who were poor sleepers experienced anticipatory anxiety in the dark, and based on the evidence, seem to be afraid of the dark,” says Carney.

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This got the researchers thinking. If some people with sleep disorders like insomnia have an active and untreated phobia of the dark, then treatment methods for some patients should be re-evaluated.

Insomniacs tend to have lots of fears that keep them up at night, and in some cases they may be traced back to a fear of the dark. “A phobia or fear of the dark is different from a fear of spiders. People don’t necessarily know they have it,” says Carney. “An individual may not be able to fall asleep once it’s dark and their mind starts to wander. They think, ‘What if someone breaks into my house?’ Instead of realizing these associations may indicate a fear of the dark, they skip a step and assume they have a fear of burglars.”

Thankfully, phobias are treatable. Most can be cured through cognitive behavioral therapy, like exposure therapy. Some people can even cure their phobias themselves without medical help.

The researchers note that there are several highly effective insomnia treatments, but that a further exploration of insomniacs’ fear of the dark may help refine them. “This is not on our radar as insomnia treatment,” says Dr. Carney. “We have very effective insomnia treatment. About 70% of patients are responsive. But, why are 30% still not responding? Why are some of these insomnia treatments not useful for some people?”

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It could be that some insomnia treatments are counterproductive for people who actually dread the dark. For instance, some of the most effective treatments encourage restless sleepers to leave their dark bedroom and go into another lit room until they feel calm or sleepy. “A phobia is maintained through avoidance,” says Dr. Carney. “By not facing the phobia, it’s going to stick around.”

The study sample was small and much more research is needed to confirm the finding, but the authors believe they have stumbled upon an unrecognized treatment need for those who toss and turn.

The study was presented Monday at SLEEP 2012, the 26th annual meeting of the Associated Professional Sleep Societies (APSS), in Boston.

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