People with depression and a type of excessive sleepiness called hypersomnolence sleep for longer periods than healthy individuals, but sleep just as well, according to a February 1 study in the Journal  of Sleep Research.

This calls into question past assumptions that people with depression experience daytime sleepiness because their sleep is fragmented and poor quality.  

The study’s lead author, David T. Plante, M.D., of the University of Wisconsin is a 2012 NARSAD Young Investigator grantee. He and his colleagues examined the sleep of 22 patients with major depressive disorder and hypersomnolence with the sleep of healthy individuals of the same age and sex. The analysis included information provided by all participants from daily sleep diaries, a wrist monitor and a monitored sleep study where the participants were allowed to sleep as long as they wanted.

Patients with depression and hypersomnolence slept longer—on average, 48.5 minutes longer—than the healthy participants, and had significantly more nap time per day. However, the researchers found no significant differences between the groups in measures of sleep efficiency-- how much of their time in bed was spent sleeping, how long it took them to go to sleep, or how often they awoke after falling asleep. Dr. Plante and colleagues found similar results when they conducted a meta-analysis – a combined study of results -- of seven past studies that included patients with hypersomnolence and depression.

The researchers note that their study “should not be construed to mean that all mood-disordered patients with a complaint of hypersomnolence will be free of sleep initiation and/or maintenance difficulties.”

They also suggest that future studies to establish the biological bases hypersomnolence in mood disorders, as well as clarify the accuracy of diagnostic thresholds to define excessive sleep duration, are needed to refine the diagnosis and treatment of these disorders.”