The significance of sleep quality in euthymic bipolar patients from Nigeria

Background Bipolar disorder is highly under-researched in Africa. Existing studies show that racial/ethnic disparities exist for sleep quality. Poor sleep quality in bipolar disorder causes significant morbidity and mortality even during periods of euthymia. Aim This study aimed to assess sleep quality and its correlates amongst euthymic patients with bipolar I disorder from Nigeria. Setting The study was carried out in a teaching hospital, and state hospital, in Ibadan, Nigeria. Method This cross-sectional study was conducted amongst 76 euthymic bipolar patients aged between 18 and 60 years, meeting the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) diagnostic criteria for bipolar disorder. Euthymia was defined as having a score of ≤ 5 on the Young Mania Rating Scale and < 8 on the Hamilton Depression Rating Scale. Sleep quality was assessed with the Pittsburgh Sleep Quality Index (PSQI). Results A total of 37 (48.7%) participants had poor quality sleep. Sleep quality was associated with marital status (p = 0.013) and suicide plan (p = 0.047). Participants with good sleep quality had higher total sleep duration, lower time to fall asleep (sleep latency), better subjective quality of sleep, were less likely to use sleep medications and had less daytime dysfunction than participants with poor sleep quality. All p-values were < 0.05. Subjective quality of sleep, ongoing use of sleep medication, daytime dysfunction were independently associated with poor sleep quality. Conclusion Poor sleep quality frequently persists during euthymic periods in patients with bipolar disorder. The correlates identified can be targeted for intervention during treatment.

http://www.sajpsychiatry.org Open Access Understanding the factors associated with sleep quality during the euthymic phase of bipolar I disorder may play a significant role in improving clinical course and help to negotiate a more favourable outcome for patients with bipolar disorder.
This study aimed to assess sleep quality and its correlates amongst well-characterised euthymic patients with bipolar I disorder.

Subjects and methods
The Mulberry study is a cross-sectional study comparing sociodemographic and clinical characteristics such as neurocognitive function, psychopathology, sleep, physical activity and spirituality between patients with bipolar disorder, patients with schizophrenia and healthy controls. 18 A complete account of the methodology has been described elsewhere. 18 The current analysis is restricted to participants with bipolar disorder in the Mulberry study. The study was carried out in a teaching hospital, and state hospital, in Ibadan, Nigeria. Assessments were carried out between February and October 2018 on 76 consecutive and consenting participants with bipolar disorder, aged between 18 and 60 years who were in remission.

Participants
While waiting to see their doctors, the research assistants personally invited successive patients attending the outpatient psychiatry clinics of the selected hospitals to participate in the study. The study was explained to them and consent was obtained. The study instruments were administered or a date was scheduled during the succeeding week when a detailed interview could be conducted.

Eligibility
To be eligible for inclusion in the current study, participants had to be euthymic and meet the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) diagnostic criteria for bipolar disorder using the Structured Clinical Interview for DSM-IV Axis I Disorders (SCID-I). A participant with bipolar disorder was deemed to be euthymic if he or she had a score of ≤ 5 on the Young Mania Rating Scale (YMRS) and had a score of < 8 on the Hamilton Depression Rating Scale (HDRS). 19 All instruments were applied by the trained research assistants.

Measures Pittsburgh Sleep Quality Index
The Pittsburgh Sleep Quality Index (PSQI) is a self-rated questionnaire designed for use in both research and clinical practice. It assesses the quality of sleep and sleep disturbances over a 1-month time interval. 20  Higher scores mean poorer quality of sleep. The seven component scores are summed up to give a global score that ranges from 0 to 21; the higher the score, the worse the quality of sleep. A global score of > 5 was used as the cut-off score between poor sleep quality and good sleep quality. 14,20 Sociodemographic and clinical assessments Important sociodemographic and clinical information was obtained from all participants. The participants were also assessed with the following instruments: 1. The Young Mania Rating Scale (YMRS) 19 2. The 17-item Hamilton Depression Rating Scale (HDRS) 21 3. The Positive and Negative Syndrome Scale (PANSS) 22

Data analysis
We carried out data analysis with the Statistical Package for the Social Science (SPSS), version 22.0 for Windows. Categorical variables were summarised using frequencies and proportions. The chi-squared test was used to analyse the relationship between two qualitative variables. Continuous variables were described using means and standard deviation (s.d.) if they were normal in type or using medians and ranges if not normally distributed. An independent sample t-test was used to assess whether there was a difference between two independent sample means, while the Mann-Whitney U test was used to compare differences between two independent groups when the dependent variable was not normally distributed.

Ethical considerations
The study was conducted following the guidelines laid down in the Declaration of Helsinki. The protocol and procedures were reviewed and approved by the Oyo State Research Ethical Review Committee (AD13/479/746).

Results
A total of 110 participants with a diagnosis of bipolar I disorder were recruited into the study, however, only 76 met the criteria for euthymia. The 76 participants (47 females, 29 male) were subsequently included in the current analysis. The mean age was 39.09 ± 11.10 years. A total of 37 (48.7%) participants had poor quality sleep during the past 1 month. There was no significant difference in socio-demographic and clinical characteristics between the group with poor sleep quality and the group with good sleep quality except for marital status and lifetime suicidal plan. A significantly higher proportion of the participants who had poor sleep quality were single or never married compared to those with good sleep quality (43.2% vs. 26.3% p = 0.013). Also, a significantly higher proportion of participants with poor sleep quality had made a suicide plan compared to those with good sleep quality (24.3% vs. 7.7% p = 0.047) (see Tables 1a and 1b).
Although the differences were not statistically significant, participants with poor sleep quality had a higher average length of an episode, used higher doses of mood stabiliser and antipsychotics per day, had lower social and occupational functioning, lower monthly income and financial net worth than participants with good sleep quality (Tables 1a and 1b).

Characteristics of sleep quality in bipolar patients
Participants with good quality sleep did significantly better than those with poor quality sleep in the seven components of the PQSI except for habitual sleep efficiency (Component 4) and sleep disturbances (Component 5). Therefore, participants with good sleep quality had higher total sleep duration, lower time to fall asleep (sleep latency), better subjective quality of sleep, were less likely to use sleep medications and had less daytime dysfunction than participants with poor sleep quality (see Tables 2a and 2b).

Regression analysis
Binary logistic regression analysis to determine the factors that were independently associated with poor sleep quality in euthymic bipolar disorder patients indicated that subjective quality of sleep, use of sleep medication, daytime dysfunction were independently associated with poor sleep quality (see Table 3).

Discussion
Nearly half (48.7%) of the euthymic bipolar I patients had poor sleep quality suggesting that many euthymic patients with bipolar disorder display substantial disturbance in sleep quality during remission. This means that about half the population of bipolar disorder patients purportedly in remission are at the risk of neurocognitive impairment, low immunity, obesity, heart disease, diabetes, infertility, poor social and occupational functioning and other effects of poor sleep quality because of impaired sleep quality. 10,11,12,13 Sleep disturbance is also a trigger for relapses and recurrences. This can lead to a vicious cycle of relapses and poor sleep quality. The result adds to existing reports indicating that euthymic bipolar patients have substantial poor sleep quality even when they are adjudged symptomatically to be in remission. 15,23,24,25,26 The prevalence of sleep quality in our study (48.7%), is lower than those of existing studies in similar euthymic patients (56.5% -82.9%). 23,27,28 Methodological differences could have accounted for the lower prevalence observed in our study.
We found that a significantly higher proportion of the participants who had poor sleep quality were single or never married compared to those with good sleep quality. This is in keeping with existing studies showing that poorer sleep quality is more commonly associated with unpartnered relationship status (single, divorced, cohabiting, widowed) than partnered relationship status (i.e. married or cohabiting). 29,30 Nevertheless, marital happiness and anxiety are confounders in the associations between sleep quality and unpartnered relationships. Marital happiness is associated with a better quality of sleep in women, 31,32 while anxiety in close relationships is associated with poorer subjective sleep quality. 33, 34 Such associations suggest that being in a partnered relationship may be beneficial to the health and well-being of patients with bipolar disorder. We found a significant association between sleep quality and a suicidal plan. This is in keeping with existing studies that found an association between suicidal behaviours and impaired quality of sleep amongst euthymic bipolar patients. 35,36 Existing studies indicate that there is an association between impaired sleep quality and suicidal ideation, suicidal attempts, and completed suicide. 37 Furthermore in males, poor sleep quality is associated with suicide attempts, but not in females. This implies that there may be sex differences in the relationship between disturbed sleep quality and suicidal behaviour. Testosterone levels and age have been implicated in this phenomenon. 38,39 It has been suggested that low testosterone level is associated with suicide in the elderly, while high testosterone level is associated with suicide in adolescents and young adults. 40 The mean sleep latency in participants with poor sleep quality in our study (25 min) was significantly higher than that for participants with good sleep quality (15 min). Additionally, it was higher than the normal 10-20 min usually found in adults. The findings regarding sleep latency are in parity with existing reports that indicate that euthymic bipolar patients have longer sleep-onset latency than during manic or depressive episodes. 41 We found evidence of a significant association between poor sleep quality and subjective quality of sleep, use of sleep medication and daytime dysfunction amongst euthymic patients with bipolar disorder. Notably, these associations remained significant after controlling for several covariates in binary logistic regression.
The finding that daytime dysfunction was independently associated with euthymic bipolar patients replicates the report on sleep by Geoffroy et al. conducted amongst euthymic bipolar disorder patients and healthy controls. The authors found poorer sleep efficiency, frequent sleep disturbances and daytime dysfunction to be associated with euthymic bipolar disorder. 42 Similarly, Cretu et al. 43 found that bipolar patients in remission compared to healthy controls had significantly worse daytime dysfunction. Earlier studies also showed similar trends, for example, Harvey et al. 25 showed that daytime dysfunction was poorer in euthymic bipolar patients compared to healthy controls.
Poor sleep quality in euthymic bipolar disorder patients was independently associated with medication use. This is There were certain limitations to this study. First is the use of PSQI which is both subjective and retrospective and may be laden with the problem of recall bias. Second, the PSQI generates a global score from its seven component scores. These components are influenced by many factors. Third, the sample size was small; this may have reduced the power of the study to detect significant differences.

Conclusion
Amongst euthymic bipolar patients, poor sleep quality frequently persists during euthymic periods and can be a focus of targeted intervention. An assessment of sleep quality should be routinely carried out in the assessment of euthymic bipolar patients.

Funding information
This work was supported by a grant from the Tertiary Education Trust Fund (TETFUND). The funder did not play any role in the design, collection, screening, interpretation, writing, and submission for publication of this study. The funder holds no responsibility for the contents of this study.