New research suggests that symptoms of depression and insomnia are the strongest predictors of having frequent nightmares.

Finnish researchers found that 3.9 percent of participants reported having frequent nightmares during the previous 30 days, including 4.8 percent of women and 2.9 percent of men. Frequent nightmares were reported by 28.4 percent of participants with severe depressive symptoms and 17.1 percent of those with frequent insomnia.

They found that the strongest independent risk factors for nightmares were insomnia, exhaustion and the depressive symptom of "negative attitude toward self."

"Our study shows a clear connection between well-being and nightmares," Nils Sandman, lead author of the study, said in a statement. "This is most evident in the connection between nightmares and depression, but also apparent in many other analyses involving nightmares and questions measuring life satisfaction and health."

For the study, researchers analyzed data from two independent cross-sectional surveys of the Finnish general adult population conducted in 2007 and 2012. Nearly 14,000 adults between 25 and 74 years of age filled out the survey. The surveys involved a questionnaire that was mailed to the participants and a health examination at the local primary health care center, where the completed questionnaire was returned and checked by a nurse. Occasional nightmares in the past 30 days were reported by more than 45 percent of participants, and 50.6 percent reported no nightmares at all.

Sandman noted that the cross-sectional study did not allow for an examination of causality. However, he suggested that the results do raise intriguing possibilities worth investigating in the future.

"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?"

The findings are detailed in the journal Sleep.