Why do people have nightmares? It's a mystery as old as sleep itself. Now a new study identifies three common risk factors that may help shed light on why some suffer frequent bad dreams.
Researchers found that people with depression, insomnia and exhaustion appear to have a higher risk of nightmares.
"Our study shows a clear connection between well-being and nightmares," lead author Nils Sandman, of the Center for Cognitive Neuroscience at the University of Turku in Finland, said in a news release. Of all of the factors studied, "depression and insomnia were the strongest predictors of frequent nightmares," the paper concludes.
For the study, published in the journal Sleep, researchers surveyed more than 13,900 people in Finland about their sleep habits and dreams. Participants, who ranged in age from 25 to 74, also underwent physical exams and completed general health questionnaires.
More than 45 percent of those studied said they had experienced nightmares at some point in the previous 30 days. Nearly 5 percent of the women and 3 percent of the men reported having frequent nightmares.
Nightmares were much more common among people with severe depressive symptoms; more than 28 percent of them reported frequent nightmares. Researchers say people with a "negative attitude toward self" were especially prone to nightmares.
Insomnia and fatigue also increased the likelihood of bad dreams, with 17 percent of insomniacs reporting frequent nightmares.
The study did not prove that depression, insomnia and fatigue actually cause nightmares -- it's possible they are to some extent a consequence of poor sleep. But Sandman believes exploring a person's dreams could provide useful clues to other aspects of health.
"It might be possible that nightmares could function as early indicators of onset of depression and therefore have previously untapped diagnostic value," he said. "Also, because nightmares, insomnia and depression often appear together, would it be possible to treat all of these problems with an intervention directed solely toward nightmares?"