The sleep of remitted bipolar outpatients: a controlled naturalistic study using actigraphy.
Millar A., Espie CA., Scott J.
BACKGROUND: Several sleep laboratory studies suggest sleep abnormalities in bipolar disorder. However, this is the first study to compare remitted bipolar subjects with controls on actigraphic and subjective sleep parameters in a naturalistic setting over 5 nights. METHODS: Nineteen subjects with Bipolar I Disorder and 19 age- and gender-matched healthy controls were included. Objective sleep parameters were estimated using wrist actigraphs. Subject-rated sleep diaries and mood ratings were also completed. Sleep data were averaged for each subject across nights, and raw score standard deviations were calculated as a measure of within-subject variability. RESULTS: Multivariate analyses of variance found significant group differences for both actigraphic (F(4,33)=3.80, P=0.012) and subjective measures (F(4,31)=3.18, P=0.027). Univariate analyses identified reliable differences in sleep onset latency (subjective), sleep duration (subjective), and variability of sleep duration and night wake time (actigraphic). Binary backward stepwise logistic regression demonstrated that a combination of three sleep measures correctly predicted disorder status in 84% of cases. LIMITATIONS: Failure to match on sociodemographic and employment status is a limitation that may provide an alternative explanation for some findings. Furthermore, in the bipolar group 18 of 19 subjects were in receipt of psychotropic medication, compared to none of the healthy control group. Also, no information was recorded about family history of mental disorders in the control group. CONCLUSIONS: The study suggests that the sleep of remitted bipolar outpatients measured in naturalistic settings is characteristically different from controls: bipolar subjects sleep longer, report longer onset latencies, and display greater variability across nights.