Research reportSleep functioning in relation to mood, function, and quality of life at entry to the Systematic Treatment Enhancement Program for Bipolar Disorder (STEP-BD)
Introduction
Bipolar disorder is a severe, recurrent, and often chronic psychiatric illness associated with significant functional impairment, morbidity, and mortality (Coryell et al., 1993) and up to 30% of bipolar patients attempt suicide (Yuan-Who and Dilsaver, 1996). Despite advances in pharmacological and psychological treatments (Angst et al., 2002, Craighead et al., 2002, Ketter, 2005), the risks of relapse and inter-episode dysfunction remain high. Thus, it is important to enhance our understanding of precipitants of mood episodes and mechanisms that may contribute to inter-episode dysfunction (Johnson, 2005).
Several lines of evidence highlight the importance of sleep disturbance in bipolar disorder. First, sleep disturbance is a core symptom of bipolar disorder and is exhibited across mood phases. During manic episodes, for example, there is a reduced need for sleep, whereas episodes of depression can involve either insomnia or hypersomnia. Second, sleep disturbances often persist despite treatment, and up to 70% of euthymic bipolar patients exhibit clinically significant sleep disturbance (Harvey et al., 2005). Furthermore, compared to healthy individuals, euthymic bipolar patients exhibit longer sleep duration and greater sleep variability (Millar et al., 2004). Third, sleep disturbance is the most common prodrome of manic episodes and not uncommonly occurs prior to the onset of depressive episodes (Jackson et al., 2003). Fourth, alterations in sleep patterns may precipitate mood episodes (Leibenluft and Suppes, 1999, Bauer et al., 2006). For example, experimentally induced sleep deprivation is associated with reductions in depressive symptoms and the onset of hypomania or mania (Benedetti et al., 2007, Benedetti et al., 2008, Colombo et al., 1999, Feldman-Naim et al., 1997 Kasper and Wehr, 1992, Wehr et al., 1987, Wirz-Justice et al., 2005, Wirz-Justice and Van den Hoofdakker, 1999, Wu and Bunney, 1990).
Our goal in this paper is to use data gathered as part of the Systematic Treatment Enhancement Program for Bipolar Disorder (STEP-BD) (Sachs et al., 2003) to determine the prevalence of disordered sleep in bipolar disorder. Our primary aim was to conduct a detailed descriptive study of two important sleep functioning parameters (duration, variability) and their relations with clinical status, function, and quality of life in patients with bipolar disorder. Given evidence that sleep deprivation has adverse consequences on performance (Pilcher and Huffcut, 1996) and mood (e.g., Wehr et al., 1987; although see Benedetti et al., 2007), we hypothesized that patients who were short sleepers (SS) would exhibit greater overall symptom severity, poorer function, and poorer quality of life relative to patients classified as normal sleepers (NS). We also hypothesized that, given literature documenting the adverse consequences of hypersomnia on functioning (Dauvilliers and Buguet, 2005), patients classified as long sleepers (LS) would exhibit poorer function and poorer quality of life relative to NS. Third, given that sleep disturbance is evident during euthymia (Harvey et al., 2005, Millar et al., 2004), we examined differences in sleep duration and variability within euthymic bipolar patients. We also explored differences in sleep duration and variability according to bipolar subtype.
Section snippets
Procedures
All participants were patients with bipolar disorder recruited as part of the STEP-BD protocol. Upon study entry, participants were provided with a complete description of the study and informed consent was obtained. Next, clinician- and patient-rated measures of sleep functioning, clinical diagnosis and course, symptom severity, function, and life satisfaction were assessed. If a patient was unable to complete a self-report measure at study entry, he or she completed it at home and returned it
Demographic and clinical characteristics across entire sample
As evident in Table 1, approximately half (55.9%) of the sample was female, the majority was Caucasian, and the mean age was 38.0 (SD = 13.1) years. Mean age at onset for bipolar illness was 16.8 years (SD = 8.8). In the past year, 26.9% of participants exhibited a rapid cycling course. With respect to clinical status, the majority of participants were syndromally depressed (36.1%) or euthymic (36.0%), followed by syndromal elevation (13.5%), subsyndromal depression (12.7%), and subsyndromal
Discussion
The first hypothesis tested was that the SS group would exhibit greater symptom severity, poorer function, and lower quality of life relative to the NS group. Indeed, SS exhibited greater symptoms of mania, depression, and anxiety compared to NS. This finding is consistent with prior research associating short sleep durations with increased mania or hypomania (Bauer et al., 2006, Colombo et al., 1999, Kasper and Wehr, 1992 Wehr et al., 1987). Interestingly, irritability was not associated with
Limitations
These results should be interpreted within the confines of several limitations. First, the cross-sectional study design precludes conclusions about causality. Future studies with longitudinal designs are warranted in order to carefully assess the potential causal relationships. Indeed, it may be the case that both short and long sleep duration are important predictors of recurrence in bipolar disorder. Second, although the available sleep-related variables from the CMF enabled us to derive
Conclusion
The present study suggests that restricted or extended sleep schedules may be associated with a pernicious symptom course in bipolar disorder. Moreover, the present findings contribute to an emerging literature suggesting that sleep may be a mechanism contributing to clinical and functional impairment in bipolar disorder.
Role of funding source
The STEP-BD study was supported with Federal funds from the National Institute of Mental Health (NIMH), under contract N01MH80001. Any opinions, findings, and conclusions or recommendations expressed in this publication are those of the authors and do not necessarily reflect the views of the NIMH.
Conflict of interest
The authors declare no conflicts of interest related to the content of this article.
Acknowledgements
The contents of this article were reviewed and approved by the Systematic Treatment Enhancement Program for Bipolar Disorder (STEP-BD) Steering Committee. Additional detail on STEP-BD can be located at: http://www.nimh.nih.gov/health/trials/practical/stepbd/questions-and-answers-for-the-systematic-treatment-enhancement-program-forbipolar-disorder-step-bd-study-background.shtml.
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