Insomniacs are at increased risk of developing major depression, results of a 20-year study demonstrate.
The findings also suggest that while insomnia frequently accompanies depression, it may not be just a symptom of depression as is commonly thought, but a separate condition, Dr Daniel J. Buysse of the University of Pittsburgh School of Medicine and colleagues say.
Depression is a well known risk factor for insomnia, and people with depression often report difficulty sleeping, Buysse and his team point out in the journal Sleep.
While some investigators have suggested that insomnia could, conversely, increase depression risk, few studies have looked at this issue over time.
To investigate, Buysse and his team looked at 591 people participating in a sleep study who were interviewed six times over the course of 21 years. When the study began, in 1978, the men were 19 years old, and the women were 20 years old.
Overall, one in five of the study participants reported having sleep problems lasting for at least one month during the follow-up period.
Women were twice as likely to experience one-month insomnia as men.
Insomnia both with and without depression was highly stable across time, meaning study participants who reported either type of sleeping difficulty at one point in the study were also likely to report it at other points.
People who had begun the study reporting short stretches of difficulty sleeping tended to report longer bouts with insomnia as time passed.
The researchers also found that having insomnia for at least two weeks increased the likelihood that a person would subsequently have a major depressive episode.
But there was no relationship between having "pure insomnia" and "pure depression" during the course of the study, suggesting that insomnia with depression may represent a subtype of both conditions.
These findings and other research findings also suggest that insomnia is not just a symptom of depression, they add, but rather an independent condition that frequently accompanies depression.
Reuters
