Abstract
There has been a growing number of studies that have employed actigraphy to investigate differences in motor activity in mood disorders. In general, these studies have shown that people with bipolar disorders (BPDs) tend to exhibit greater variability and less daytime motor activity than controls. The goal of this study was to examine whether patterns of motor activity differ in euthymic individuals across the full range of mood disorder subtypes (Bipolar I (BPI), Bipolar II (BPII) and major depression (MDD)) compared with unaffected controls in a community-based family study of mood spectrum disorders. Minute-to-minute activity counts derived from actigraphy were collected over a 2-week period for each participant. Prospective assessments of the level, timing and day-to-day variability of physical activity measures were compared across diagnostic groups after controlling for a comprehensive list of potential confounding factors. After adjusting for the effects of age, sex, body mass index (BMI) and medication use, the BPI group had lower median activity intensity levels across the second half of the day and greater variability in the afternoon compared with controls. Those with a history of BPII had increased variability during the night time compared with controls, indicating poorer sleep quality. No differences were found in the average intensity, variability or timing of activity in comparisons between other mood disorder subgroups and controls. Findings confirm evidence from previous studies that BPI may be a manifestation of a rhythm disturbance that is most prominent during the second half of the day. The present study is the largest study to date that included the full range of mood disorder subgroups in a nonclinical sample that increases the generalizability of our findings to the general community. The manifestations of activity patterns outside of acute episodes add to the accumulating evidence that dysregulation of patterns of activity may constitute a potential biomarker for BPD.
Highlights
The greater variability and reduced daytime activity among people with Bipolar I (BPI) disorder are consistent with accumulating evidence that bipolar disorders (BPDs) may be a manifestation of a circadian rhythm disturbance.[2,14,22,32,45,46]
Our finding of greater differences between BPD and controls in daytime rather than nighttime activity suggests that these patterns extend beyond disrupted patterns of sleep, which has been the primary focus of earlier studies.[13,16]
The manifestations of activity patterns outside of acute episodes in both probands and their relatives[19,33,34] combined with evidence from studies of people with increased vulnerability to BPD14,30,47 or genetic liability to BPD28,48 provide evidence that dysregulation of activity may constitute a potential endophenotype for BPD.[49]
Summary
Actigraphy, a reliable, non-invasive[1,2] and objective method to monitor 24-h patterns of motor activity over time[3] has been increasingly used in both community and clinical studies of chronic diseases such as diabetes,[4] heart disease[5] and dementia.[6]Actigraphy has been used to study neuropsychiatric disorders, affective disorders,[7,8,9] and attention deficit hyperactivity disorders.[10,11] Most research on mood disorders has employed actigraphy as an index of sleep onset, offset or quality rather than as a direct measure of 24-h patterns of motor activity.[1,12,13,14,15,16,17] There has been a growing number of studies of individuals with bipolar disorder (BPD),[18,19,20,21,22,23,24,25,26,27,28] major depression (MDD)[7,29] and those at risk for BPD14,30,31 that have employed actigraphy to investigate differences in 24-h patterns of activity associated with mood disorders, as recently summarized by Scott et al 32 In general, these studies have shown that people with BPD tend to exhibit greater variability and less daytime motor activity than controls. Actigraphy, a reliable, non-invasive[1,2] and objective method to monitor 24-h patterns of motor activity over time[3] has been increasingly used in both community and clinical studies of chronic diseases such as diabetes,[4] heart disease[5] and dementia.[6]. Aggregation of the data across these studies is complicated by the substantial differences in the goals, procedures, samples and statistical methods,[36] estimates of average and variability in daily activity.[7,37,38] The majority of studies of mood disorders have been based on relatively small clinical samples of patients with BPD. We examined the association between mood disorder subtypes and objectively measured motor activity in a large community-based family study, the National Institute of
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