For some people with insomnia, the source of their sleeplessness may be an unexpected one.
New Canadian research suggests fear of the dark may be behind the sleepless nights that some insomniacs experience.
The research is preliminary and the scientists say more studies will be needed to gauge how big a problem this is and whether it affects women and men across various age groups.
But if they are right, it could be good news for some insomnia sufferers. Phobias like fear of the dark can be successfully treated with cognitive behavioural therapy, said senior author Colleen Carney, director of the Sleep and Depression Laboratory at Ryerson University in Toronto.
"We don't ask about this. We don't assess for this phobia and we don't treat the phobia. And we could," said Ms. Carney , who is presenting her team's study today at a major sleep medicine conference in Boston.
The idea is the result of a couple of threads of thought coming together. Ms. Carney said she had noticed a lot of the patients her lab sees sleep with a light on or with a TV or computer on in the bedroom. And she started to remark that some people with insomnia talked about the dark in phobic terms.
So the group decided to try to see if there was anything to the idea. But they figured asking insomniacs flat out if they were afraid of the dark wouldn't work. Most people would be too embarrassed to own up to the fear, they felt.
So they designed a test to objectively measure whether poor sleepers were more fearful in the dark than good sleepers.
As it turned out, quite a few of the 93 participants in the trial did admit to being afraid of the dark – around half of the poor sleepers, in fact. Fewer than 20 per cent of good sleepers said they were afraid of the dark. The median age of participants was 22 years old.
The objective test involved having poor and good sleepers spend time in the sleep lab, both in darkness and in light. At random intervals, a noise was blared through the headphones participants wore, and the researchers recorded information on whether the subjects were visibly startled by the noise.
In the light, both groups reacted the same way to the noise. But in the dark phase of the trial, good sleepers became habituated to the noises, but poor sleepers had stronger reactions.
"In the dark, the poorer sleepers were more startled by it. And they became increasingly scared as the experiment went on," she said.
At a point they also used what Ms. Carney called a pre-pulse – a faint noise that signalled that the louder one was coming. For the poor sleepers, it actually seemed to increase their dread of the impending noise.
"We have now objective and subjective evidence that for some people fear of the dark is a significant part of this, because basically it means the bed time and night period, they are already going to be coming in with tension," Ms. Carney said.
"Because of what it is, right? You've got to turn the lights off."
Sleep medicine specialist Dr. Colin Shapiro found the work persuasive, calling it "a neat, small study, but one that will give us clues about ways to try and psychologically help people with insomnia problems." Shapiro was not involved in the research.
Ms. Carney says knowing this is important for a couple of reasons. Firstly, as she noted, phobias can be treated. Secondly, a commonly used approach for insomnia may need to be altered – it might actually be making the fear of the dark problem worse, she said.
People with sleep problems are told not to stay in bed if they can't fall asleep. It's recommended that they go to another room – a lit room – and read or do some other activity until they become sleepy.
"So we are actually facilitating avoidance, which is actually how phobias maintain themselves," she suggested.