Quality of Life Research 13: 783–791, 2004. Ó 2004 Kluwer Academic Publishers. Printed in the Netherlands.
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Perceived quality of life in schizophrenia: Relationships to sleep quality Michael Ritsner1,2, Rena Kurs1, Alexander Ponizovsky1 & Jack Hadjez1 1 Sha’ar Menashe Mental Health Center, Hadera (E-mail:
[email protected]); 2Bruce Rappaport Faculty of Medicine, Technion, Haifa, Israel Accepted in revised form 27 April 2003
Abstract We examined the relationship between perceived quality of life (QOL) and subjective quality of sleep among schizophrenia patients, and its relation to symptom severity, side effects and emotional distress. One hundred and forty five schizophrenia patients were comprehensively evaluated with standardized measures of symptom severity, adverse effects, emotional distress, QOL, and sleep quality (the Pittsburgh Sleep Quality Index, PSQI). Partial correlation and multiple regression analyses were performed. Poor sleepers reported lower mean scores on all QOL domains, they were more depressed and distressed, and had more adverse effects to medications with concomitant distress than good sleepers. The negative relationship between complaints of poor sleep quality and QOL measures remained significant when the confounding effect of depression, side effects, and distress was partialled from the correlation matrix. Daytime dysfunction (a component of the PSQI) accounted for 12.6% of the variance in QOL index scores. Thus, poor QOL reported by schizophrenia patients is substantially associated with poor sleep quality. This association appears both independently and synergistically with depression, distress and side effects of medications.
Key words: Depression, Distress, Quality of life, Schizophrenia, Sleep
Introduction During the past two decades, the concept of quality of life (QOL) has become an important outcome measure in schizophrenia. While there is no universal operational definition of perceived QOL, most researchers agree that QOL is a nonspecific perception of all aspects of individual existence [1], an indicator of subjective well-being and satisfaction [2], and a dimension of mental health [3]. Oliver et al. [4] conceptualized QOL as an evaluation of life as a whole, based on a balance between individual needs and fulfillment. QOL related factors have been intensively investigated among individuals with schizophrenia [5–7]. Factors associated with poor QOL of schizophrenia patients can be summarized as follows: negative symptoms [8, 9], general psychopathology [10, 11], depressive symptoms [6], emotional and somatic
distress [12, 13], medication side effects [14], duration of illness and hospitalizations [15]. Poor sleep quality has been recognized as an important construct associated with poor QOL for members of the general population [16–18] and patients with cardiac and pulmonary pathologies [19, 20], cancer [21], cirrhosis [22] endometriosis [23], Parkinson’s disease [24], and narcolepsy [25]. Although schizophrenia patients have reported both poor life and poor sleep quality more often than members of the general population [26–31], to the best of our knowledge, the relationship between sleep quality and QOL outcomes in schizophrenia have not yet been investigated. Obtained QOL data were interpreted in the framework of a ‘clinical’ model involving symptoms, medication side effects and psychosocial performance [32–36], and distress/protection [12] model. The specific contribution of sleep quality to
784 QOL appraisal in these models was not previously explored. The present study aimed to test the hypothesis that low QOL and poor sleep quality among schizophrenia patients would be associated independent of the influence of distress, side effects, depression and other symptoms. To test this hypothesis, we first compared QOL domain scores between poor and good sleepers; second, we evaluated the relationship between QOL and quality of sleep ratings before and after partialling out the effects of distress, side effects, depression and other symptoms; and, finally, we determined the contribution of sleep quality components for prediction of QOL ratings.
Methods
were separated, divorced or widowed. Of 145 patients, 101 presented with paranoid type (295.3), 27 with residual type (295.6), eight with disorganized type (295.1), eight with undifferentiated type (295.9), and one with catatonic type. Mean age at application to psychiatric care was 22.9 years (SD ¼ 7.2), mean duration of disorder was 15.0 years (SD ¼ 9.1), and mean number of hospitalizations was 7.8 (SD ¼ 4.5, range 1–15). All patients received regular treatment with atypical (n ¼ 69), conventional (n ¼ 76) and both (n ¼ 16) antipsychotics, antidepressants (n ¼ 21), or anxiolytics (n ¼ 38). Of 145 patients 59 patients were assessed during hospitalization in rehabilitation settings, 45 – at discharge from hospital, and 41 – in outpatient clinics. All patients were physically healthy, with recent normal physical examinations, and normal blood and urine laboratory test results.
Study design Measures We drew a sample from the database of patients participating in an ongoing naturalistic prospective investigation; the Sha’ar Menashe Longitudinal Study of QOL, involving patients with major psychiatric disorders. A detailed description of the design, data collection, measures and cross-sectional findings was reported elsewhere [12–14]. Inclusion criteria were DSM-IV schizophrenia, age 18–65 years, and the ability to provide written informed consent. Patients with comorbid mental retardation, organic brain diseases, severe physical disorders, drug/alcohol abuse, and those with low comprehension skills were not enrolled. The Sha’ar Menashe Internal Review Board and the Israel Ministry of Health approved the study. All participants signed informed consent for participation in the study, after receiving a comprehensive explanation of study procedures. Subjects For the present study data of 145 stable schizophrenia patients who completed the Pittsburgh Sleep Quality Index (PSQI) were used. The sample was 81.4% male (n ¼ 118), with mean age 38.2 years (SD ¼ 9.6; range ¼ 19–59 years), and mean length of education 10.2 years (SD ¼ 2.7). A total of 66.2% of the patients (n ¼ 96) were single, 16.6% (n ¼ 24) were married, and 17.2% (n ¼ 25)
The Schedule for Assessment of Mental Disorder (SAMD) [12], a semi-structured interview, was used to collect comprehensive clinical data covering (1) background and demographic characteristics, (2) family and personal psychiatric history, (3) details of present illness and medication, (4) general medical history, and (5) current laboratory tests. The Positive and Negative Syndrome Scale (PANSS) [37] is a psychiatric rating scale for the assessment of severity of positive (ranged 7–49), negative (ranged 7–49), and general (ranged 16– 112) symptoms; higher ratings indicate a severe psychopathology. Inter-rater reliability for the PANSS dimensions as measured by intra-class correlation coefficient ranged from 0.79 to 0.93. For the entire sample, the PANSS total mean score was 82.3 ± 20.8 demonstrating a considerable general severity of psychopathology. Severity of depression was evaluated with the Montgomery and Asberg Depression Rating Scale (MADRS) [38]. We used MADRS total score range 0–60 [12], higher ratings indicate more severe depression. Inter-rater reliability for the MADRS was 0.86. To evaluate subjective parameters of nocturnal sleep, we asked the patients to complete the PSQI, a self-rating questionnaire for assessing sleep
785 quality and disturbances relating to the previous month [39]. The PSQI was chosen because it is a widely used standardized measure of subjective quality of sleep [40, 41]. It has 19 individual items that generate 7 ‘component’ scores for subjective sleep quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbances, use of sleep medication, and daytime dysfunction as well as the PSQI total score. A cut-off point of five on the PSQI total score was used to separate good (PSQI < 5) from poor (PSQI P 5) sleepers [39]. Subjective QOL was assessed using the QOL Enjoyment and Satisfaction Questionnaire [42], a 93-item self-report measure of the degree of enjoyment and satisfaction in the following domains: physical health, subjective feelings, leisure time activities, social relationships, and general activities, work, household duties, medication satisfaction, and school/course, and life satisfaction and enjoyment. The questionnaire uses a 5-point scale with higher ratings indicating better QOL. In the current study, we used only seven of the Q-LES-Q domains excluding household duties, school/ courses and work scales as irrelevant for hospitalized patients. The Perceived QOL index, reported here, is an average score of the 60 items included in these seven domains. The Talbieh Brief Distress Inventory [43], a selfreport questionnaire of 24 items drawn from previously developed scales [44, 45], was used for measuring the degree of overall psychological discomfort experienced by the patients. Responses are scored on a 5-point scale, with higher ratings indicating higher intensity of distress. Apart from the demonstrable validity and reliability, the TBDI was chosen because it is easy to administer, brief, and readily understood by mentally ill patients [46]. The internal consistency reliability for each self-report instrument, as measured by Cronbach’s coefficient a ranged from 0.87 (PSQI) through 0.93 (TBDI index) to 0.95 (QOL index, Q-LES-Q). Pharmacological treatments were recorded for the month prior to assessment. The severity of adverse effects of medication as well as psychological response to them were measured with the Distress Scale for Adverse Symptoms (DSAS) [12, 14], a clinician administrated rating scale consisting of a checklist of 22 of the most frequently observed side effects during treatment with antipsychotics. Responses are scored on a 5-point
scale, with higher scores indicating higher severity and greater distress attributed to the given side effect. Three indices were computed: Number of Adverse Symptoms (NAS, Cronbach’s a ¼ 0.87), Mental Distress Index (MDI, a ¼ 0.78), and Somatic Distress Index (SDI, a ¼ 0.85). Statistical analysis All analyses were performed with the NCSS-2000 [47]. Differences in means (SD) and proportions were tested with two-tailed t-tests and v2 statistics, respectively. Pearson product moment correlation was calculated to examine the relationship between sleep quality and perceived QOL domains. To test the possible influence of depression, adverse events of medication, and distress on the relationship between quality of sleep and life scores of these variables were partialled from the correlation matrix. Multiple regression analysis was performed with the QOL index as a dependent variable and seven PSQI components (subjective sleep quality, sleep latency, sleep duration, sleep efficiency, sleep disturbances, sleep medication usage, and daytime dysfunction) as independent variables. Backward stepwise selection was performed with variable selection and removal p-values > 0.05, in order to find the most parsimonious model for predicting QOL outcomes.
Results Comparison of poor and good sleepers Since inpatients and outpatients had similar ratings on the PSQI (5.5 ± 4.2 vs. 6.3 ± 4.2, respectively, t ¼ 0.95, p ¼ 0.34) and on QOL index (3.6 ± 0.8 vs. 3.4 ± 0.7, respectively, t ¼ 1.43, p ¼ 0.16), we combined these two subgroups for the following analyses. Of the entire sample, 66 patients were considered ‘poor sleepers’ (45.4%; the PSQI >5) and the remaining 79 patients were ‘good sleepers’. No differences in prevalence of poor sleepers between in- and outpatients were found (45.2 and 46.3%, respectively, v2 ¼ 0.016, df ¼ 1, p ¼ 0.90). The between-group comparisons showed that poor sleepers reported a significantly lower satisfaction with life in general and life specific do-
786 Table 1. Differences in quality of life domains and clinical measures between good and poor sleepers Dimension
Good sleepers N = 79
Poor sleepers N = 66
t-value
Mean
SD
Mean
SD
Q-LES-Q Physical health Subjective feelings Leisure time activities Social relationships General activities Satisfaction with medicine Quality of Life Index
49.0 57.4 23.5 41.2 52.4 4.0 3.9
9.3 11.3 6.1 9.6 10.9 0.9 0.6
40.8 45.4 18.4 33.2 42.0 3.4 3.1
10.8 12.4 6.4 9.6 10.2 1.2 0.7
4.8* 6.0* 4.9* 5.0* 5.9* 3.2** 6.5*
PANSS Positive symptoms Negative symptoms General psychopathology
14.8 25.7 39.1
5.4 7.4 11.1
16.5 26.8 42.6
6.3 6.8 10.4
1.8 0.9 1.9
MADRS (total score)
3.9
3.2
7.5
7.1
3.2***
TBDI (distress index)
0.8
0.7
1.5
0.8
5.9*
DSAS Number of adverse symptoms Mental distress index Somatic distress index
0.2 0.2 0.1
0.2 0.3 0.2
0.4 0.4 0.3
0.3 0.4 0.3
3.5* 2.9** 2.9**
Q-LES-Q = the Quality of Life Enjoyment and Satisfaction Questionnaire; higher scores indicate a better satisfaction with quality of life.PANSS = the Positive and Negative Syndrome Scale; higher ratings indicate a severe psychopathology. MADRS = Montgomery and A¨sberg Depression Rating Scale; higher ratings indicate a severe depression. TBDI = the Talbieh Brief Distress Inventory; higher scores indicate a severe emotional self-reported distress. DSAS = the Distress Scale for Adverse Symptoms; higher ratings indicate a severe side effects. Good sleepers = PSQI < 5; Poor sleepers = PSQI P 5. t-tailed t-tests: * p < 0.001; ** p < 0.01; *** p < 0.05.
mains than good sleepers (Table 1). Likewise, poor sleepers were more depressed and distressed than those without sleep disturbances. However, no significant differences between groups were observed in positive, negative, and general symptoms’ ratings. Although the groups received comparable defined daily doses of medications (data not shown), poor sleepers reported a greater number of adverse effects of antipsychotic medications and associated mental and somatic discomfort. Correlation analysis There was no correlation between the PSQI total score and severity of positive and negative symptoms as measured by the PANSS. By contrast, correlations of sleep quality with levels of depression (r ¼ 0.32) and overall distress (r ¼ 0.52), as well as with the number of adverse effects of
medications, and associated mental and somatic discomfort (r ¼ 0.35–0.43) were all highly significant (all p < 0.001). Complaints of poor sleep quality and QOL measures demonstrated moderate negative relationships (r ranged from )0.32 to )0.53) with all life quality domains (Table 2, left column). Partial correlations between these variables remained statistically significant (though somewhat decreased in magnitude) after controlling for depression and medication side effect-induced distress. However, the correlations substantially declined in magnitude and partly lost significance after adjusting for overall level of experienced emotional distress. Finally, when the intervening variables (MADRS, DSAS and TBDI) were controlled together, the relationships between sleep quality and QOL index and general activities’ domain scores remained significant (both r ¼ )0.19, p < 0.05).
787 Table 2. Pearson’s correlations between quality of sleep and quality of life measures before and after adjusting for depression, adverse effects of medications, and psychological distress Q-LES-Q
Quality of Sleep Index (PSQI) Before adjusting for
Physical health Subjective feelings Leisure time activities Social relationships General activities Satisfaction with medicine Quality of Life Index
)0.49* )0.48* )0.38* )0.34* )0.50* )0.32* )0.53*
After adjusting for Depression (MADRS)
Adverse effects (DSAS)
Distress (TBDI)
)0.41* )0.41* )0.28** )0.24** )0.41* )0.28** )0.45*
)0.33* )0.34* )0.28** )0.27** )0.39*** )0.23** )0.40*
)0.22** )0.15 )0.12 )0.08 )0.19*** )0.19*** )0.23**
Q-LES-Q = the Quality of Life Enjoyment and Satisfaction Questionnaire; higher scores indicate a better satisfaction with quality of life. PSQI = the Pittsburgh Sleep Quality Index; higher scores indicate less satisfaction with sleep. MADRS = Montgomery and A¨sberg Depression Rating Scale; higher ratings indicate a severe depression. TBDI = the Talbieh Brief Distress Inventory; higher scores indicate a severe emotional self-reported distress. Significance test: * p < 0.001; ** p < 0.01; *** p < 0.05.
Multiple regression analysis
Discussion
To determine which components of sleep would predict better QOL outcomes in schizophrenia patients, multiple regression analysis with QOL index as the dependent variable and PSQI dimensions as independent variables was performed (Table 3). Only two of seven PSQI components predicted life quality outcome, while the remaining five components seemed insignificant. The significant predictors were daytime dysfunction accounting for 12.6% of the total variance in the individual QOL index scores, and subjective quality of sleep that accounted for only 1.6% of the total variance.
This study is the first to examine the relationship between perceived QOL and subjective quality of nocturnal sleep in a substantial sample of schizophrenia patients. We found that complaints of poor sleep quality presented a frequent problem among schizophrenia patients. Prevalence figures of poor sleepers (45%) found in this study are higher than rates previously reported in the general population (20– 30%) [17, 48, 49]. Our findings also confirm previous reports concerning correlation of sleep quality with depressive symptoms [28, 29, 31], adverse effects of medications [30] and psycho-
Table 3. Summary of stepwise regression analysis for predicting Quality of Life indexa (dependent variable) from sleep quality components Predictor
Standardized estimation (b)
t-value (b = 0)
% Total variance accounted for
)0.26 )0.12 )0.03 0.02 )0.09 0.06 )0.36
2.8** 1.5 0.3 0.2 1.1 0.9 4.4***
1.6 – – – – – 12.6
b
PSQI Subjective sleep quality Sleep latency Sleep duration Sleep efficiency Sleep disturbances Sleep medication usage Daytime dysfunction
Model significance: R2 = 41.5%; F = 13.8, df = 7, p < 0.0001. The Quality of Life Enjoyment and Satisfaction Questionnaire; higher scores indicate a better satisfaction with quality of life. b PSQI = the Pittsburgh Sleep Quality Index; higher scores indicate less satisfaction with sleep. Probability level: * p < 0.001; ** p < 0.01; * p < 0.05. a
788 logical distress associated with various conditions [50–52]. We did not find correlations between PSQI total scores and the severity of positive, general and negative symptoms, a finding that may be explained by the lack of fluctuation in the current clinical states of most of the patients. The major finding of this study is that the overall QOL indices as well as satisfaction with each specific life domain are correlated with quality of sleep scores: the poorer the sleep quality the poorer the perceived QOL. This association is congruent with data obtained in the general population and among patients with various medical conditions [16–18, 20, 24]. Poor sleep quality might be negatively associated with QOL ratings in two ways: (1) acting synergistically with depression, distress and side effects, and (2) independently. Both these assumptions were confirmed in the present study. We found that schizophrenia patients with prominent sleep complaints were more distressed and depressed, had a greater number of adverse events of medications and accompanying mental and somatic discomfort than those who had no sleep complaints. Overall quality of sleep was moderately correlated with current levels of depression and side effects, and highly correlated with the distress index. There are several explanations for the confounding effects of distress, depressive symptoms, and side effects of medication on the sleep quality/ life quality relationship. First, stress and depression are the leading causes of insomnia [53] and thus may substantially contribute to the association between sleep and life quality. Second, impaired sleep, resulting in daytime dysfunction may be an important additional source of stress for many individuals, setting up a vicious, selfperpetuating cycle [54]. Third, adverse effects of medication including sleep disturbances may induce additional distress influencing this association. Finally, all of the above factors have been shown to be important determinants of the QOL in chronic schizophrenia patients [6–8, 12– 14, 55]. To test the hypothesis that low QOL and poor sleep quality among schizophrenia patients may be independently associated, depression, distress and side effect ratings were partialled from the correlation matrix. According to partial correlations depression and adverse effect scores did not reduce
the sleep-life quality relationship, but controlling exclusively for emotional distress in this manner, significantly reduced the association between sleep quality and satisfaction with subjective feelings, leisure time activities and social relationships. Finally, after adjusting for potential covariate effects (MADRS, DSAS and TBDI), satisfaction with overall QOL and the general activities’ domain still remained significantly associated with sleep quality. We conclude that there is an independent association between subjective QOL and subjective quality of sleep. How may poor sleep quality influence QOL ratings? Several abnormalities in sleep architecture have been described in schizophrenia. For instance, a slow-wave sleep (SWS) deficit and a shortened rapid eye movement (REM) sleep stage have been commonly observed in schizophrenia patients [56–58]. Longitudinal findings suggest that SWS parameters are relatively stable during follow-up, while REM parameters seem to change, perhaps in relation to the phase of illness and treatment [59]. Shortened REM latency and disturbed sleep continuity represent reversible state abnormalities, while reduced SWS may represent a more persistent trait abnormality among schizophrenia patients [59–61]. We hypothesized that SWS deficit may be associated with poor QOL of schizophrenia patients. Future research is expected to clarify the nature of the sleep-life quality relationship. Finally, of all the PSQI components of impaired sleep, daytime dysfunction appears to be the most meaningful predictor of QOL index ratings in schizophrenia patients. Thus, daily consequences of subjective disturbed nocturnal sleep (reduced well-being and functioning) may have a positive predictive value for subjective life quality outcomes at least in the given group of schizophrenia patients. It is surprising that none of the existing QOL models consider the contribution of sleep quality to life dissatisfaction of schizophrenia patients [33–36, 55]. According to the distress/protection model [12, 14], resultant QOL is an outcome of the interaction between an array of distressing, and putative distress protective factors. Since sleep may be a protective factor, impaired sleep may contribute to decreased QOL. As shown in the present study poor sleep quality is negatively associated with QOL ratings in two ways: inde-
789 pendently and acting synergistically with depression, distress and side effects. The main limitations of the study should be addressed. It is based on cross-sectional data and involves no intervention that might provide stronger support for the obtained relationships. To determine the nature and direction of causality, it is necessary to demonstrate that increased subjective sleep quality increases QOL and vice versa. This problem will hopefully be resolved as our longitudinal study progresses. We could not collect data from acute psychotic patients who were unable or refused to participate in the study, a common problem in studies using self-report methodology in severely ill psychiatric patients. Findings of this study have important clinical and research implications. They raise the question whether treatment efforts directed towards the amelioration of symptoms adequately address the need to improve subjective QOL of schizophrenia patients. Inasmuch as controlling for morbid symptoms is an important clinical goal, our findings suggest that the contribution of symptoms to patients’ appraisal of subjective QOL is relatively limited. Interventions focusing on the reduction of psychological discomfort may contribute to improved sleep satisfaction, leading to better daytime function, and better subjective QOL outcomes. Further investigation of different strategies for improving sleep quality that would lead to improved QOL among schizophrenia patients is needed. Acknowledgements We wish to thank our research assistant Michal Z’ada.
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Address for correspondence: M. Ritsner, Mobile Post Hefer 38814, Sha’ar Menashe Mental Health Center, Hadera, Israel Phone: þ972-4-6278750; Fax: þ972-4-6278025 E-mail:
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