ABSTRACT
Despite sleep disturbance and somatic symptoms being common health complaints, the relationship between these disturbances and single somatic symptoms is not well documented. The objectives of this study were to (i) identify somatic symptoms that are particularly associated with sleep disturbance, here referred to as somatic symptoms related to sleep disturbance (SS-SD), (ii) determine increased risk of sleep disturbance for each SS-SD and for a certain number of SS-SD, with and without controlling for anxiety and depression, and (iii) determine sensitivity and specificity for identifying sleep disturbance based on number of SS-SD in a general Swedish sample. Population-based, cross-sectional data based on validated questionnaire instruments were used from participants who constituted a sleep disturbance (n = 864) or a reference (n = 2340) group. Among 15 common somatic symptoms, stomach pain, back pain nausea/gas/indigestion, dizziness, and constipation/loose bowels/diarrhea were identified as SS-SD, with odds ratios of increased risk of sleep disturbance that ranged from 1.93 to 2.44 (1.36–1.79 and 1.54–1.91 when controlled for anxiety and depression, respectively). The risk of sleep disturbance increased by 1.44 times for each SS-SD (1.25 and 1.30 when controlled for anxiety and depression, respectively). A cutoff of two/three or more SS-SD had a sensitivity of 72.5/54.2% and a specificity of 50.0/69.7% for identifying sleep disturbances. When patients present with these somatic symptoms with or without a pathophysiological explanation, primary care clinicians may consider screening for sleep disturbance.
Sleep disturbance refers to persistent difficulties initiating sleep, frequent awakenings and inability to return to sleep. Its prevalence ranges from 6% to about one-third depending on operationalization and population (Sivertsen et al., Citation2009). Negative impact includes cognitive functioning (Killgore, Citation2010) and increased risk of serious diseases, such as type-2 diabetes (Anothaisintawee et al., Citation2016) and cardiovascular disease (Canivet et al., Citation2014) as well as psychiatric disorders, such as anxiety (Cox & Olatunji, Citation2016) and depression (Steiger & Pawlowski, Citation2019). Although sleep disturbance is highly prevalent, it remains underdiagnosed, undertreated and neglected (Bragg et al., Citation2019; Grandner & Chakravorty, Citation2017).
The main dimensions of sleep disturbance are poor sleep quality (SQ) and non-restorative sleep (NRS) (Harvey et al., Citation2008; M. Nordin et al., Citation2013; Roth et al., Citation2010). Poor SQ is commonly referred to as poor ease of sleep onset and sleep maintenance, insufficient sleep time and early awakening (Grima et al., Citation2019; Harvey et al., Citation2008), and NRS to be insufficiently rested, or refreshed for satisfactory daytime functioning (Roth et al., Citation2010).
Somatization is another common condition, since about one-third of all somatic symptoms reported in primary care are pathophysiologically unexplained (Jackson & Passamonti, Citation2005). Among patients at a psychosomatic clinic, as many as 56% reported sleep disturbance (Mutsuhiro & Takeaki, Citation2018). The relationship between sleep disturbance and symptoms in a general sense is well documented. For example, sleep disturbance is predicted by body pain, it correlates with number of and severity of somatic symptoms, and is associated with functional somatic syndromes (Kim et al., Citation2001; Schlarb et al., Citation2017; Zhang et al., Citation2012). However, the relationship between sleep disturbance and specific somatic symptoms is not well documented (Wei et al., Citation2018). Nevertheless, in a Japanese study using three questionnaire items to assess sleep disturbance, all eight studied somatic symptoms were found to be associated with sleep disturbance, of which weight loss, epigastric discomfort, headache, fatigue, tachycardia/dyspnea and dizziness showed two-fold odds ratios or more (Kim et al., Citation2001). In another Japanese study, which also used three questionnaire items to assess sleep disturbance, all investigated nine somatic symptoms were found to be associated with sleep disturbance, but with small odds ratios (1.20–1.40; Asai et al., Citation2006).
Identifying subsets of somatic symptoms that are particularly associated with sleep disturbance, and determining the extent to which a certain number of somatic symptoms are indicative of being at risk for sleep disturbance may assist in the process of screening and assessing sleep disturbance in primary care.
Using data from a general Swedish sample, the first objective was to identify somatic symptoms that are particularly associated with sleep disturbance, here referred to as somatic symptoms related to sleep disturbance (SS-SD). It was also investigated whether SS-SD is associated with both poor SQ and NRS. A second objective was to determine the increased risk of sleep disturbance for each individual SS-SD and for a certain number of SS-SD, conducted with and without controlling for anxiety and depression. A third objective was to determine sensitivity and specificity for identifying sleep disturbance based on the number of SS-SD.
Materials and methods
Population and sample
Cross-sectional data were used from the population-based Västerbotten Environmental Health Study. All participants were residents in the county of Västerbotten in northern Sweden. A random sample of 8,520 individuals aged 18–79 years were invited, of which 40% (n = 3406) agreed to participate. The sample was stratified for sex and the age strata 18–29, 30–39, 40–49, 50–59, 60–69 and 70–79 years (Palmquist et al., Citation2014). Among the 3406 participants, 202 were excluded due to having responding to less than 50% of the items in the questionnaire instruments assessing sleep disturbance, somatic symptoms, depression and/or anxiety, resulting in a final sample of 3204 participants. This arbitrarily chosen percentage was used since it has been used in a similar study of somatic symptoms associated with mental ill-health (Carlehed et al., Citation2017).
Questionnaire instruments
Seven items of the Karolinska Sleep Questionnaire (KSQ) were used to identify sleep disturbance: difficulties falling asleep, repeated awakenings with difficulties falling asleep again, premature awakenings, disturbed/restless sleep, difficulties waking up, not well-rested on awakening, and feelings of being exhausted on awakening. The first four items correspond to poor SQ and the remaining three to NRS (Nordin et al., Citation2013). All items are responded to on a Likert-scale with the alternatives ‘(0) never’, ‘(1) seldom (occasionally)’, ‘(2) sometimes (several times per month)’, ‘(3) often (1–2 times per week)’, ‘(4) most of the time (3–4 times per week)’ and ‘(5) always (5 times or more per week)’. Based on DSM-V criteria, and similar to insomnia, sleep disturbance was considered present if a participant reported either ‘(4) most of the time (3–4 times per week)’ or ‘(5) always (5 times or more per week)’ on at least one of these items. A sleep disturbance score was calculated as the mean across the seven items, a poor SQ score as the mean across its four items, and a NRS score as the mean across its three items The KSQ has good validity and internal consistency (Nordin et al., Citation2013).
A Swedish version (S. Nordin et al., Citation2013) of the Patient Health Questionnaire 15-item Somatic Symptom Severity Scale (PHQ-15) (Kroenke et al., Citation2002) was applied to assess somatic symptoms. It includes 14 of the 15 most common somatic complaints (Kroenke et al., Citation2010). Severity of each symptom during the past 4 weeks are rated as either ‘Not bothered at all (0)’, ‘Bothered a little (1)’ or ‘Bothered a lot (2)’. The global score is calculated as the sum of ratings across items, with a high score indicating a high prevalence of typical somatization symptoms. A somatic symptom was considered present if it was rated as either ‘Bothered a little (1)’ or ‘Bothered a lot (2)’ on that item. The PHQ-15 has good validity and reliability (Nordin et al., Citation2013).
A Swedish version (Lisspers et al., Citation1997) of the Hospital Anxiety and Depression Scale (HADS) (Zigmond & Snaith, Citation1983) was used to quantify levels of anxiety (HADS-A) and depression (HADS-D) in the past week. Each subscale consists of seven items, none being somatic symptoms, that are rated on a 4-point scale, and range from 0 to 21 in global score (high score indicating high level of anxiety and depression). HADS has good discriminant and concurrent validity and good internal consistency (Bjelland et al., Citation2002).
Procedure
The questionnaire was sent to the participants to be returned via postal mail with prepaid postage. Invited participants who did not respond to the invitation received up to two reminders. All participants responded during the period March–April 2010, before the onset of the pollen season in Västerbotten.
The study was approved by Umeå Regional Ethics Board (Dnr 09–171 M), and was conducted in accordance with the Declaration of Helsinki. All participants gave their informed consent to participate.
Statistical analysis
Missing values were imputed five times using the fully conditional Markov Chain Monte Carlo method. The percentage of missing values was 0.7% for the KSQ, 0.9% for the PHQ-15 and 0.3% for the HADS.
Independent sample t-tests and chi-square analyses were performed to test differences between the two groups in background variables, total PHQ-15 score, number of PHQ-15 symptoms, and prevalence of specific PHQ-15 symptoms.
Spearman correlation coefficients were calculated between rating on somatic symptom severity (0–2) for each PHQ-15 item and score (0–5) on sleep disturbance, poor SQ and NRS. This enabled identification of the SS-SD and assessment of associations based separately on the poor SQ and NRS subscales. Inclusion among the SS-SD also required adequate or better concurrent validity (r ≥ 0.20) with sleep disturbance score (Evers et al., Citation2013). The number of such symptoms was limited to the integer closest to the mean number of symptoms reported on the PHQ-15 for the total sample. The PHQ-15 items ‘trouble sleeping’ and ‘feeling tired/having low energy’ were excluded from the selection of SS-SD due to falling within the definition of sleep disturbance.
Logistic regression analyses were conducted to study the risk of sleep disturbance separately for each specific SS-SD and for a number of prevalent SS-SD. These analyses were based on four models: (i) unadjusted, (ii) adjusted for the demographic variables age, sex, married/living with partner, having children aged ≤18 years, having children aged ≤6 years, education and physical exercise, (iii) adjusted for the demographic variables and HADS-A score, and (iv) adjusted for the demographic variables and HADS-D score.
Finally, sensitivity, specificity and correct classification rate (CCR) were calculated for each possible number of SS-SD. Applying equal weight on sensitivity and specificity, the CCR was the average across the two measures. The α-level was set at 0.05. SPSS (Version 26. Armonk, NY) was used for analyses.
Results
Study samples
The sleep disturbance group consisted of 864 participants, and the remaining 2340 constituted a reference group. The two groups and the total study sample are described in . Compared to the referents, the sleep disturbance group was significantly younger and consisted of a larger extent of participants who were women, not married or living with a partner, had children aged 17 years and younger and 6 years and younger, had a university education, and did not exercise ≥2 times/week. The sleep disturbance group also rated their health as poorer, scored higher on anxiety and depression, and were more likely to have reported being given a lifetime psychiatric diagnosis by a physician.
Table 1. Characteristics of the sleep disturbance and reference groups and the total study sample. Differences between the sleep disturbance and referent groups were tested with t-test and chi-square analysis
Prevalence of somatic symptoms
displays mean score on the PHQ-15, mean number of somatic symptoms, and prevalence of each somatic symptom. The PHQ-15 score, the number of symptoms and the prevalence of all symptoms were significantly higher in the sleep disturbance group compared to the referents (p < 0.001).
Table 2. PHQ-15 score, number of somatic symptoms, and prevalence of each PHQ-15 symptom in the sleep disturbance and reference groups and the total study sample. Differences between the sleep disturbance and referent groups were tested with t-test and chi-square analysis (p < 0.001 in all cases)
Correlations between sleep disturbance and somatic symptoms
Spearman correlation coefficients between rating on somatic symptom severity for each PHQ-15 item and score on sleep disturbance, poor SQ and NRS for the total sample are given in . Since the mean number of somatic symptoms in the total sample was 4.72 (), five symptoms were selected for the SS-SD. When excluding the symptoms of feeling tired/having low energy and trouble sleeping, the five symptoms with the strongest correlation with sleep disturbance score were stomach pain, back pain, dizziness, constipation/loose bowels/diarrhea, and nausea/gas/indigestion, constituting the SS-SD. All five SS-SD had a correlation coefficient of r ≥ 0.20 with scores on sleep disturbance, poor SQ and NRS, which did not motivate a separate SS-SD for the two sleep disturbance subscales.
Table 3. Spearman correlation coefficients between rating on somatic symptom severity and scores on sleep disturbance, poor sleep quality (SQ) and non-restorative sleep (NRS; p < 0.001 in all cases)
Odds ratios for specific SS-SD and number of SS-SD
presents ORs for increased risk of sleep disturbance for each specific SS-SD and for each model. The ORs differed significantly (p < 0.01) from unity for all SS-SDs in all four models. The ORs ranged between 2.04 and 2.46 when unadjusted, between 1.93 and 2.44 when adjusted for demographic variables, between 1.36 and 1.79 when adjusted for demographic variables and HADS-A score, and between 1.54 and 1.91 when adjusted for demographic variables and HADS-D score. The ORs decreased when adjusting for HADS-D score, and even more when adjusting for HADS-A score. In general, dizziness had the highest ORs and constipation/loose bowels/diarrhea had the lowest ORs among the SS-SD.
Table 4. Odds ratios (95% confidence intervals) for increased risk of sleep disturbance are based on four models (p < 0.01 in all cases)
ORs (95% confidence intervals) for increased risk of sleep disturbance for each additional number of SS-SD was 1.48 (1.40–1.56) when unadjusted, 1.44 (1.36–1.53) when adjusted for demographic variables, 1.25 (1.18–1.33) when adjusted for demographic variables and HADS-A score, and 1.30 (1.23–1.38) when adjusted for demographics. Based on these ORs, having all five SS-SD showed an OR of 7.10, 6.19, 3.05, and 3.71 for the four models, respectively. All ORs differed significantly from unity (p < 0.001).
Sensitivity and specificity
Sensitivity, specificity and correct classification rate for the identification of sleep disturbances based on the number of SS-SDs are presented in . A cutoff of three or more SS-SD had the highest CCR (62.0%), for which 54.2% were correctly identified as having sleep disturbance, and 69.7% were correctly identified as not having sleep disturbance.
Table 5. Sensitivity, specificity and correct classification rate (CCR) in percentage for identifying sleep disturbance based on a certain number of somatic symptoms among the somatic symptoms related to sleep disturbance (SS-SD)
Discussion
An association between sleep disturbance and overall somatic symptom severity was found, which is in accordance with prior findings (Zhang et al., Citation2012). The results based on both group differences and correlational analyses further showed that all somatic symptoms in the PHQ-15 were associated with sleep disturbance. The somatic symptoms that were most strongly associated with sleep disturbance, the SS-SD, were stomach pain, back pain, nausea/gas/indigestion, dizziness, and constipation/loose bowels/diarrhea, in that order. Their relatively strong correlation with score on both the poor SQ and NRS subscales did not motivate separate SS-SD for the two subscales. When adjusting for the impact of demographic variables, the increased risk of sleep disturbance (OR) ranged between 1.93 and 2.44. The ORs for three of these symptoms have earlier been reported to range between 1.21 and 1.32 (Asai et al., Citation2006). Their lower ORs compared to those in the present study may be due to use of a less strict criterion for sleep disturbance (having had sleep disturbance for at least one vs 3 months). Notably, three SS-SD are gastrointestinal. Thus, having several gastrointestinal symptoms appear to be particularly common in sleep disturbances. This is supported by post-hoc, pairwise Spearman correlation analyses of the extent of these three symptoms among those with sleep disturbances, showing coefficients ranging between 0.44 and 0.64.
We controlled for anxiety and depression. Although the ORs were larger than unity, they decreased when controlling for depression, and more so when controlling for anxiety. Notably, levels of anxiety and depression as well as prevalence rates of diagnosis of generalized anxiety disorder, panic disorder and depression were higher in the sleep disturbance group than in the referent group. This implies that underlying anxiety and depression may have contributed to the symptom severity of sleep disturbance. Accordingly, there is overlapped in diagnostic criteria between sleep disturbance, anxiety and depression, for which all three diagnoses include criteria related to sleep difficulties and lack of energy/feeling tired (American Psychiatric Association, Citation2013). This is in line with the perspective of sleep disturbances being derived from psychopathology, such as anxiety and depression (Croicu et al., Citation2014). Not surprisingly, stomach pain, nausea/gas/indigestion, constipation/loose bowels/diarrhea feeling, in addition to tired/having low energy and trouble sleeping, have been reported to be particularly associated with anxiety and depression (Carlehed et al., Citation2017).
The risk of sleep disturbance increased by 1.44 times for each additional SS-SD, resulting in an over 6 times increased risk of sleep disturbance if having all five SS-SDs. This latter number fell to 3–4 when adjusting for anxiety and depression. Clearly, the number of SS-SDs quite strongly affects the risk of sleep disturbance.
When equally weighted in sensitivity and specificity, the highest CCR was found for three or more SS-SDs. However, based on this criterion, only 54% were correctly identified as having sleep disturbance. This relatively poor sensitivity shows that the clinical utility of screening for sleep disturbances based only on this criterion is limited. This is reasonable given that sleep disturbance is best explained by a multitude of circumstances, such as psychiatric conditions, dysfunctional cognitions and maladaptive sleep habits (Kaplan et al., Citation2017). However, if the purpose is simply to determine whether further screening is needed, poor specificity may not be a major issue. Hence, in these cases the criterion of two or more SS-SD may be used, providing a sensitivity of 72.5% and a specificity of 50.0%. An alternative is to use the PHQ-15 items feeling tired/having low energy and trouble sleeping, which, not surprisingly, were found to be strongly related to sleep disturbance.
The results indicate that sleep disturbance is associated with coexisting symptoms of somatization. Sleep disturbance should be treated with the cessation of the underlying somatic symptoms that may be disturbing sleep (Johansson et al., Citation2016). Clinicians should therefore be attentive of possible comorbid somatization in encounters with sleep disturbances in order to discern the most effective alternative for treatment. It is of interest to note that the sleep disturbance group not only reported poor self-rated health, but also relatively high prevalence of diagnoses of chronic fatigue syndrome, back/joint/muscle disorder, and exhaustion syndrome. These are conditions that may contribute to sleep disturbance and/or be caused partly by sleep disturbance.
The strengths of the study include a large sample size, being population-based, and the fact that the county of Västerbotten has an age and sex distribution that is very similar to that of Sweden in general (Statistics Sweden, Citation2010). The limitations include a relatively low response rate (40%), which may result in selection bias with consequences for the representativeness. However, the effects of low response rates have been shown to vary very little between response rates of 30–70% (Galea & Tracy, Citation2007). Another limitation is the cross-sectional design of the study, which does not enable analysis of causal direction. Although not a limitation per se, different results may have been obtained if the questionnaire instrument for assessing sleep disturbance had been replaced with objective methods, such as polysomnographic recordings over a long period.
Conclusions
Despite limitations, the results suggest that all PHQ-15 somatic symptoms are associated with sleep disturbancein particular, stomach pain, back pain, nausea/gas/indigestion, dizziness, and constipation/loose bowels/diarrhea, apart from tired/having low energy and trouble sleeping, and that the risk of sleep disturbance increases considerably with number of symptoms. Whereas having three of these symptoms provides the highest CCR, an alternative criterion may be two symptoms for a reasonably good sensitivity. When patients present with these somatic symptoms, with or without a pathophysiological explanation, primary care clinicians should consider screening for sleep disturbance.
Acknowledgments
We gratefully acknowledge Eva Palmquist for valuable help with the database. This is an extension of an undergraduate thesis by Gustav Nordin and Robin Sundqvist.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Data availability statement
Data are available upon request.
Additional information
Funding
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