Clinical significance of mobile health assessed sleep duration and variability in bipolar disorder
Introduction
Disturbances in the quantity of sleep are common among patients diagnosed with bipolar disorder. Between 70 and 99% of bipolar patients experience a reduced need for sleep at some time during the course of their illness (Harvey et al., 2009). Many patients also report difficulties with falling asleep or staying asleep over the course of illness resulting in reduced or variable sleep duration. The influence of sleep duration on mood symptoms in bipolar disorder is complex—some studies show reduced and more variable sleep duration precede manic or depressive episodes (Barbini et al., 1996, Fava and Kellner, 1991, Gruber et al., 2011, Jackson et al., 2003, Perlman et al., 2006), and are evident during mood episodes (Cassidy et al., 1998), suggesting that abnormal sleep duration can be both a risk marker and a concomitant of bipolar episodes.
The majority of studies examining sleep in bipolar disorder have employed retrospective global measures of sleep duration collected over relatively short periods of observation. Some studies have employed prospective designs in which sleep and affect are measured concurrently over periods of one or several weeks (Bauer et al., 2006, Gershon et al., 2012, Gonzalez et al., 2014). These studies suggest that sleep and circadian disruptions are predictive of mood changes among people with bipolar disorder, which, in turn, has informed the basis of psychosocial interventions designed to stabilize sleep-wake patterns (Frank et al., 2005). Consistent with the idea that more variable sleep predicts more symptoms in bipolar disorder, Gruber et al. (2011) found in a sample of 196 remitted patients reporting on the maximum and minimum duration of sleep obtained in the previous week, that greater variability in sleep duration was associated with worsening of depression and mania across a one-year follow up period. Seemingly consistent with these data on individuals with bipolar disorder, among healthy individuals, reduced or more variable sleep duration over time is associated with a worsening of mood (Dinges et al., 1997), diminished well-being (Drake et al., 2001) and cognitive impairment (Boland and Alloy, 2013). Poor sleep has also been linked to lower medication adherence in individuals with serious medical conditions (Phillips et al., 2005), although no studies have examined this potential link, to our knowledge, in bipolar disorder. It remains unclear if between person differences in sleep duration variability are adequately captured in brief observation periods and across a range of levels of depressive and manic symptom severity. Additionally, more studies are needed to assess the dimensional components of bipolar disorder (Phillips and Kupfer, 2013). For example, depression has been characterized by low levels of positive affect, rather than high levels of negative affect (Dunn et al., 2004), whereas mania is characterized by high levels of positive affect or irritability, but not necessarily low levels of negative affect. Examining mood symptoms alone may obscure the subtleties of these affective dimensions in bipolar disorder.
Moreover, past studies have not yielded opportunities to examine proximal associations between sleep and mood. Sleep duration and variability has typically been evaluated with cross-sectional surveys (Goossens et al., 2010), and longitudinal studies with time points spaced months, or even years, apart (Gruber et al., 2011, Perlman et al., 2006, Saunders et al., 2015). Studies have employed actigraphy to measure sleep in bipolar patients, but sleep duration in these studies was only measured for one or two weeks (Harvey et al., 2005, Jones et al., 2005, Millar et al., 2004) and concurrent mood ratings were collected at one time point (Harvey et al., 2005, Jones et al., 2005) or by daily mood diary entries (Gershon et al., 2012, Millar et al., 2004). Mobile technology and ecological momentary assessment, the frequent real time and concurrent assessment of naturalistic behavior and affective experience, affords the ability to examine proximal associations between day-to-day sleep duration and variability and concurrent positive and negative affect. In addition, lagged models enable understanding of the potential carryover effects of impaired sleep on affect.
Data from a clinical trial in bipolar disorder with a comprehensive baseline characterization and 11-weeks of daily assessments of sleep and affect via smart phone surveys allowed us to more thoroughly examine the relationship of sleep duration and variability to symptom severity, medication adherence, global cognitive functioning, and longitudinally assessed positive and negative affect. We hypothesized lower average sleep duration would be positively correlated with baseline manic symptom severity and inversely correlated with baseline depressive symptom severity. We also predicted higher day-to-day variability in sleep duration would be associated with greater baseline manic and depressive symptom severity, lower medication adherence, and greater cognitive impairment. Finally, we hypothesized that day-to-day change in sleep duration and in how atypical the day’s sleep duration was compared to the person’s norm would predict increases in same-day and next-day negative affect and decreases in same-day and next-day positive affect.
Section snippets
Parent study
Data came from a randomized controlled trial of outpatients with bipolar I and II disorder in San Diego, which compared use of an automated mobile device-delivered intervention following brief psychoeducation with brief psychoeducation alone (Depp et al., 2015, Depp et al., 2012). Only subjects in the active arm (n = 41) were included. This study was carried out in accordance with the Declaration of Helsinki, and informed consent was obtained by all participants. The study was approved by the
Results
Demographic characteristics are displayed in Table 1. Participant ages were on average in the mid-to late-40s. Participants were balanced by sex, and the majority were white, few were married, and most were living independently in the community. The vast majority of participants were diagnosed with bipolar I (vs. II), and generally had an age of onset of bipolar disorder in the early 20s. Most participants were medicated.
Discussion
This study assessed how sleep duration and variability are related to mood symptoms, medication adherence, cognitive functioning and daily affect using ecological momentary assessment. We found greater person-averaged sleep variability was associated with greater depression and mania symptom severity and with lower self-reported medication adherence as measured at baseline, but not with global cognitive function. In other words, more severely symptomatic and less adherent patients reported more
Author contributions
Dr. Kaufmann wrote the manuscript and conducted statistical analyses. Dr. Gershon wrote the manuscript and provided feedback on statistical analyses. Dr. Eyler wrote the manuscript and provided feedback on statistical analyses. Dr. Depp wrote the manuscript, provided feedback on statistical analyses, and served as the parent study Principle Investigator. All authors have approved the final submitted article.
Conflicts of interest
None.
Role of funding sources
This study received funding from the National Institute of Mental Health (Grant #’s: T32MH019934, K23MH077225, R34MH091260, R01MH100417, K01MH100433, R01MH103318). The funding agencies listed did not have any role in the collection, analysis and interpretation of data; in the writing of the report; and in the decision to submit the article for publication.
Acknowledgement
None
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