April 3, 2008
Science Daily/American Academy of Sleep Medicine
A new study confirms the persistent nature of insomnia and the increased risk of subsequent depression among individuals with insomnia.
According to the results, the annual prevalence of one-month insomnia increased gradually over time, with a cumulative prevalence rate of 20 percent and a greater than two-fold risk among women. In 40 percent of subjects, insomnia developed into more chronic forms over time. Insomnia either with or without comorbid depression was highly stable over time. Insomnia lasting two weeks or longer predicted major depressive episodes and major depressive disorder at subsequent interviews.
Seventeen to 50 percent of subjects with insomnia lasting two weeks or longer developed a major depressive episode reported in a later interview. "Pure" insomnia and "pure" depression were not longitudinally related to each other, whereas insomnia comorbid with depression was longitudinally related to both.
"We used to think that insomnia was most often just a symptom of depression. However, a growing body of evidence suggests that insomnia is not just a symptom of depression, but that it may actually precede depression. In other words, people who have insomnia but no depression are at increased risk for later developing depression. This study adds to our knowledge by including a much longer follow-up period than most previous studies," said Daniel J. Buysse, MD, of the University of Pittsburgh, lead author of the paper.
"We were also able to look separately at insomnia alone, depression alone, and combined insomnia-depression. The results show that insomnia seems to be followed by depression more consistently than the other way around. In addition, we found that insomnia tended to be a chronic problem that gets more persistent over time, whereas depression was a more intermittent problem."