Both objective and subjective features of sleep differ between people with bipolar disorder who are currently euthymic and healthy controls, a case–control study has found.
The findings add further weight to the hypothesis that sleep and circadian rhythms are disrupted in bipolar disorder and are a potential therapeutic target in strategies to prevent relapse.
Pierre Geoffroy (Hôpital Albert Chenevier, Créteil, France) and co-workers sought to overcome the methodological limitations of previous studies by using actigraphy to assess objective sleep quality in 26 people with bipolar disorder (currently in remission) and 29 psychiatrically healthy control individuals matched for age and gender.
For 21 consecutive days, all participants wore an actigraph to measure their gross motor activity; on each of these days they also recorded their subjective sleep quality using the Pittsburgh Sleep Quality Index (PSQI) and kept a sleep diary.
Results showed that the bipolar disorder patients and healthy individuals were equivalent with regard to body mass index, risk of sleep apnoea, daytime sleepiness and severity of mood symptoms.
However, several subjective measures of sleep differed between the groups. Specifically, the total PSQI score was significantly higher in bipolar disorder patients than controls, at 7.38 versus 4.11, as were PSQI subscales measuring subjective sleep quality, habitual sleep efficiency, sleep disturbances and daytime dysfunction.
Many objective sleep measures, documented with actigraphy, also differed between the groups and again indicated a greater frequency of sleep disturbance among people with bipolar disorder.
Compared with healthy controls, bipolar disorder patients had a significantly longer sleep duration (475.4 vs 455.8 min), longer sleep latency (25.2 vs 11.6 min), poorer sleep efficiency (81.5 vs 84.9%), a greater fragmentation index (32.0 vs 28.7), and worse inter?daily stability (0.50 vs 0.51).
In linear regression modelling, four variables were associated with bipolar disorder: mean sleep duration; mean sleep latency; variability in fragmentation index over 21 days and mean score on PSQI daytime dysfunction. Together, these four variables correctly classified 89% of the study participants as cases or controls, note the researchers.
Writing in the Journal of Affective Disorders, they conclude: “These findings indicate that future studies should examine both the mean scores and the variability over extended periods of time. In addition, we show that a combination of subjective and objective measures (quantity and variability) may be a better circadian biosignature of [bipolar disorder] than any single measure on its own.”
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