The differential effects of gratitude and sleep on psychological distress in patients with chronic pain

Abstract

This study aimed to examine the possible cross-sectional mediating role of sleep in the relationship of gratitude with depression and anxiety in patients with chronic pain. A total of 224 patients with chronic pain completed structured questionnaires assessing chronic pain, depression and anxiety symptoms, gratitude, and sleep disturbances. Results of multiple regression analyses yielded a modest mediating effect for sleep on the gratitude–depression link whereas a stronger mediating effect was found for sleep on the gratitude–anxiety link. These data show much of the effect of gratitude on depression was direct whereas sleep exerted a stronger mediating effect on the gratitude–anxiety link.

Keywords

anxiety chronic pain depression gratitude mediating sleep

Introduction

There is a high level of psychiatric comorbidity with sleep disturbances and/or insomnia. Between 50 and 90% of subjects diagnosed with depression complain of poor sleep quality (Hetta et al., 1985; Riemann et al., 2001). While insomnia has been widely considered as a major factor affecting the course of depression, there are data suggesting that it is similarly a risk factor for the development of depression (Chang et al., 1997; Roberts et al., 2000). Compared to people without insomnia, people with insomnia had a higher risk of committing suicide whereas suicide completers as compared to controls had a higher rate of sleep disturbances both the week preceding death and in the current depressive episode (Goldstein et al., 2008).

Recently, research has suggested the positive influence of gratitude on psychological well-being and sleep quality. As a personality trait, gratitude is defined as ‘a sense of thankfulness and joy in response to receiving a gift, whether the gift be a tangible benefit from a specific other or a moment of peaceful bliss evoked by natural beauty’ (Emmons and McCullough, 2004). Higher gratitude is significantly associated with higher positive affect but lower physical symptoms (Froh et al., 2009; McCullough et al., 2002). Grateful people also reported lower depression and anxiety (Watkins et al., 2008). Compared to their lower gratitude counterparts, individuals with higher gratitude had longer sleep duration (Emmons and McCullough, 2003) and better sleep quality (Wood et al., 2009).

One possible explanation for the positive influence of gratitude on psychological well-being and sleep quality is grateful people tend to adopt positive coping strategies such as positive reframing to deal with stress (Wood et al., 2007a, 2007b). Perceiving and interpreting a stressful stimulus that was previously viewed as negative in a positive light (Lambert et al., 2009), grateful individuals were more likely than less grateful ones to have positive pre-sleep cognition, which was found to be a protective factor of sleep disturbances (Wood et al., 2009). Despite this preliminary evidence for the link of gratitude with psychological well-being and sleep, we found no publication that clarifies the nature of gratitude’s influence on sleep and psychological well-being.

This cross-sectional study aimed to fill these research gaps by examining the relationships between gratitude, sleep and psychological distress (including depression and anxiety). In a sample of patients with chronic pain, we (1) compared the pain and psychological characteristics between participants with and without insomnia, and (2) tested the possible mediating role for sleep in the relationship between gratitude and psychological distress. Gratitude was hypothesized to be the predictor in this study as it is dispositional and shows little variation due to circumstances (Emmons and McCullough, 2004; Wood et al., 2008). As pre-sleep cognition was the underlying mechanism that explained the relationship between gratitude and sleep (Wood et al., 2009), sleep in this study was hypothesized to be the mediating factor in the relationship between gratitude and psychological distress. Chronic pain is a significant public health problem both in terms of the numbers of people affected and the enormous social and economic implications for the health care system and society. In addition to its deleterious effects on general health (Becker et al., 1998) and physical functioning (Guitera et al., 2002), chronic pain is also a strong predictor of future mortality (Andersson, 2004; Currie and Wang, 2004). People with chronic pain reported greater use of general medical services (Eriksen et al., 2003), consuming medical services up to five times more frequently than the rest of the population (VonKorff et al., 1991). The examination of the differential influence of gratitude and sleep on psychological distress in the chronic pain population is of clinical significance since sleep disturbances are common symptoms among patients with chronic pain (Tang et al., 2007; Wong et al., 2011). Research also suggested that chronic pain, insomnia, and psychiatric disorders are mutually influential, with each increasing the risk of onset of the others (Breslau et al., 1994; Lipton et al., 2000). Examining the nature of the gratitude–sleep–psychological distress relationship could inform efforts to improve and monitor psychological well-being among patients with chronic pain.

Method

Participants

Following Institutional Review Board, consecutive patients attending for musculoskeletal pain problems at an orthopedics specialist outpatient clinic of a public hospital were invited for participation in the study. Criteria for patients’ eligibility included: (1) ≥18 years of age; (2) native Cantonese speakers; (3) lacking communication problems or physical conditions preventing completion of interview; (4) exhibiting no confusion and having no prior diagnosis of cognitive impairment from medical records; and (5) willing to participate in the study and to give written consent. Face-to-face interviews were conducted by trained research assistants with eligible patients during visits for clinical consultations with doctors.

A total of 224 (of 238 eligible patients; 94% of patients approached) patients with chronic pain were recruited in this study. Over half of the sample was female (56.9%), married/cohabiting (60.6%), engaged in full-time work (55.2%), and not endorsing a religion (53.5%). The mean age of the sample was 45.66 years (SD = 9.84; range: 19–61) and about 42% of the sample fell in the age group of 50–59 years. Nearly 46% of the sample had monthly family income ≤HK$20,000.¹

Measures

Pain intensity and disability

The seven-item Chronic Pain Grade (CPG) Questionnaire assesses three dimensions of pain severity in the past three months: intensity; disability/interference; and persistence (VonKorff et al., 1990). Pain intensity was assessed by asking participants to rate their present, average, and worst pain intensity on an 11-point Numerical Rating Scale (NRS) (0 = ‘no pain at all’; 10 = ‘pain as bad as could be’). A Characteristic Pain Intensity Score is derived by averaging the responses to the intensity items and multiplying this by 10. Three CPG items assess pain interference with (1) daily activities, (2) social activities, and (3) working ability using 0–10 NRSs (0 = ‘No interference/change’; 10 = ‘Unable to carry on activities/extreme change’). The CPG Disability Score is derived by multiplying the average of the three interference items by 10. Persistence was assessed in the original CPG by asking the respondent to indicate the number of days out of the past three months that he/she was disabled by pain. The Disability Score and the number of disability days are recoded into four-point scales (Disability Score: 0 = ‘0–29’, 1 = ‘30–49’, 2 = ‘50–69’, 3 = ‘≥70’; Disability Days: 0 = ‘0–6 days’, 1 = ‘7–14 days’, 2 = ‘15–30 days’, 3 = ‘≥31 days’) and summed, yielding ‘Disability Points’. The CPG classifies respondents into five hierarchical grades (see Table 1). Both the English and Chinese version of the CPG possess good psychometric properties (VonKorff et al., 1990; Wong and Fielding, 2011).

Table 1.

Pain and psychological characteristics of the sample

Pain characteristics	Entire sample	Participants insomnia	Participants without insomnia	Group difference
No. of pain sites, M(SD)	2.53 (1.59)	2.39 (1.04)	1.80 (0.90)	–3.61**
1	33.5	26.3	50.0
2	23.2	23.7	22.0
3–4	31.2	34.6	26.0
≥5	11.1	15.4	2.0
Pain duration (year); M(SD)	4.35 (6.05)	4.30 (6.00)	4.96 (6.61)	0.66
≥3 months–2 years	55.7	56.3	53.3
>2–5	20.3	21.2	15.6
>5 –10	12.3	11.9	13.3
>10	11.8	10.6	17.8
Pain intensity, M(SD)
Present pain	2.88 (2.68)	3.40 (2.74)	1.42 (1.90)	–4.66**
Average pain	5.36 (2.17)	5.61 (2.13)	4.42 (2.00)	–3.43*
Worst pain	7.66 (2.30)	7.80 (2.15)	7.15 (2.60)	–1.76
Pain interference, M(SD)
Daily activity	5.35 (2.88)	5.72 (2.61)	4.24 (3.31)	–3.26*
Social activity	4.71 (3.28)	5.28 (3.08)	3.08 (3.21)	–4.35**
Working ability	5.66 (3.51)	6.37 (3.23)	3.86 (3.50)	–4.69**
Pain-associated disability (day); M(SD)	52.40 (27.84)	57.88 (25.52)	37.27 (26.77)	–4.91**
Chronic Pain Grade classification^a				17.13*
Grade zero	21.0	13.5	40.0
Grade I	12.1	13.5	8.0
Grade II	18.7	19.9	16.0
Grade III	16.5	17.3	14.0
Grade IV	31.7	35.9	22.0
Gratitude	31.06 (7.68)	30.79 (7.97)	32.42 (6.48)	1.29
Psychological distress; M(SD)
Depression	5.92 (5.32)	5.83 (4.65)	1.84 (2.41)	–5.81**
Anxiety	4.74 (4.55)	7.25 (5.39)	2.20 (2.85)	–6.34**

Note: Figures are percentage unless otherwise stated; M, mean; SD, standard deviation; Gratitude was indexed by the GQ-6; Depression and anxiety were indexed by the HADS.

Grade zero: Pain free; Grade I: low disability–low intensity; Grade II: low disability–high intensity; Grade III: high disability–moderately limiting; Grade IV: high disability–severely limiting.

p < .05; ^**p < .001.

Psychological distress

The 14-item Hospital Anxiety and Depression Scale (HADS) was designed to assess affective and behavioral symptoms of depression (HAD-D) and anxiety (HAD-A) (Zigmond and Snaith, 1983). All HADS items are rated on a four-point Likert scale. The total score (ranging from 0–21) is the sum of the score of all items in each subscale, with higher scores indicating greater morbidity. Leung et al. (1999) and Zigmond and Snaith (1983) reported the HADS possessed good psychometric properties (r ≥ 0.89; Cronbach’s α ≥ 0.90).

Gratitude

The Gratitude Questionnaire-Six-Item Form (GQ-6) (McCullough et al., 2002) was used to measure individual differences in experience gratitude in daily life. Rating on a seven-point Likert scale, the GQ-6 assesses the intensity, frequency, span and density of gratitude. The total score ranges from 1–42 with higher scores indicating more grateful. McCullough et al. (2002) reported that the GQ-6 possessed good psychometric properties (αs ranging 0.76–0.84).

Insomnia

The Pittsburgh Sleep Quality Index (PSQI) measures individuals’ sleep quality in the month prior to the study (e.g. ‘During the past month, how often have you had trouble staying awake while driving, eating meals, or engaging in social activity?’, ‘How would you rate your sleep quality overall?’) (Buysse et al., 1989). Rating on a four-point Likert-scale, the scale consists of 19 items which generate seven ‘component’ scores (including ‘subjective sleep quality’, ‘sleep latency’, ‘sleep duration’, habitual sleep efficiency’, ‘sleep disturbances’, ‘use of sleeping medication’, and ‘daytime dysfunction’), and a global PSQI score ranging from 0–21 with higher scores indicating poorer subjective sleep quality. As established by Buysse et al. (1989), people with insomnia was classified based on PSQI global score ≥ 5. A previous study demonstrated that the PSQI has an acceptable internal consistency (α = 0.83), validity, and test–retest reliability (Tsai et al., 2005).

Statistical analyses

Differences between participants with and without insomnia on pain and psychological characteristics were assessed using independent-sample t-tests/chi-square tests. A series of multiple regression analyses were performed to determine the effect of gratitude and sleep on psychological distress. For sleep to be a mediator of the gratitude–depression link (Model 1), the four criteria proposed by Baron and Kenny (1986) needed to be met: (1) gratitude should significantly predict sleep; (2) gratitude should significantly predict depression; (3) sleep should significantly predict depression after controlling for gratitude; and (4) after controlling for sleep, the relationship between gratitude and depression should be decreased or become non-significant. Perfect mediation is established if the association between gratitude and depression is reduced to zero. If results of regression analyses suggested a partial mediation, a Sobel test (MacKinnon et al., 2002) would be employed to determine whether the indirect path between gratitude and depression was statistically significantly different from zero. These criteria were also applied to test the effect of sleep on the relationship between gratitude and anxiety (Model 2). Preselection for entry of sociodemographic variables into the multivariate models required a p-value of < .05 in univariate regression analyses. The results of multicollinearity tests suggested low multicollinearity among predictor variables on depression and anxiety. Pain variables including number of pain sites, pain intensity (indexed by Characteristic Pain Score), and pain disability (indexed by Pain Disability Score) were included in all multivariate models to control for potential confounding effects. Data analyses were performed using SPSS Windows 17.0.

Results

Pain and psychological characteristics

The present sample had an average of 2.53 (SD = 1.59) pain sites, with 65.5% multiple pain sites (Table 1). Patients reportedly experienced an average of 4.35 years (SD = 6.05) of pain problems and an average of 52.40 (SD = 27.84) days of pain-associated disability. The CPG classified 48.2% of the sample as Grade III or above. Based on the PSQI global score cutoff at ≥ 5, 76.1% of the sample was classified as having insomnia. Compared to participants without insomnia, participants with insomnia reported significantly more pain sites, higher present and average pain intensity, higher pain interference, and greater pain-associated disability (all p < .05). The proportion of participants with insomnia being classified as Grade III or above in the CPG (53.2%) was significantly higher than that of participants without insomnia (36%; χ² = 17.13, p < .05). Participants with insomnia also scored significantly poorer on HADS-D and HADS-A scores than those without insomnia (all p < .001).

Sleep as a mediator between gratitude and psychological distress

As shown in Table 2 (Model 1), higher gratitude was significantly associated with lower depression (β = −0.19, p < .01) and better sleep (β = −0.09, p < .005). Sleep was significantly associated with depression (β = 0.35, p < .001), suggesting poorer sleep quality was associated with more depressive symptoms. When sleep was controlled, gratitude was significantly associated with depression (β = −0.17, p < .01) (Sobel z = −3.44, p < .001) (Fig. 1).

Table 2.

Mediation analysis on the effects of sleep on the relationship between gratitude and psychological distress

Test of mediation pathway	β	SE	95% CI
Model 1: The Gratitude–Sleep–Depression Pathway ^a
Gratitude (Predictor)→Depression (Outcome)	–0.19**	0.04	–0.26, –0.12
Sleep (Mediator)→Depression (Outcome)→Gratitude (Predictor)^b	0.35***	0.07	0.20, 0.49
Gratitude (Predictor)→Sleep (Mediator)	–0.09*	0.04	–0.17, –0.01
Gratitude (Predictor)→Depression (Outcome)→Sleep (Mediator)^c	–0.17**	0.04	–0.24, –0.10
Sobel test	z = −3.44***
Model 2: The Gratitude–Sleep–Anxiety Pathway ^d
Gratitude (Predictor)→Anxiety (Outcome)	–0.11*	0.05	–0.20, –0.02
Sleep (Mediator)→Anxiety (Outcome)→Gratitude (Predictor)^b	0.54**	0.07	0.39, 0.69
Gratitude (Predictor)→Sleep (Mediator)	–0.09*	0.03	–0.17, –0.05
Gratitude (Predictor)→Anxiety (Outcome)→Sleep (Mediator)^c	–0.06	0.04	–0.15, 0.02
Sobel test	z = −2.12*

Note: β: beta coefficient; SE: standard error; CI: confidence interval.

Regression equations were controlled for education level, employment status, family income, number of pain site, and pain intensity.

The hypothesized predictor, gratitude, was controlled in the regression equation.

The hypothesized mediator, sleep, was controlled in the regression equation.

Regression equations were controlled for education level, number of pain site, and pain intensity.

p < .05; **p < .01; ***p < .001

Figure 1.

The mediation analysis for the relationship between gratitude, sleep, and depression

In Model 2, higher gratitude was significantly associated with lower anxiety (β = −0.11, p < .05) and better sleep (β = −0.09, p < .05). Sleep was significantly associated with anxiety (β = 0.54, p < .01), indicating poorer sleep quality was associated with more anxiety symptoms. After controlling for sleep, gratitude was no longer significantly associated with anxiety (β = −0.06, NS) (Sobel z = −2.12, p < .05) (Fig. 2).

Figure 2.

The mediation analysis for the relationship between gratitude, sleep, anxiety

Discussion

We believe this is to be the first study to examine the effects of gratitude and sleep on psychological distress among patients with chronic pain. Our results show that up to 76.1% of the patients with chronic pain in this Chinese sample were identified as having insomnia. After controlling for potential confounding factors, sleep mediated the effects of gratitude on depression and anxiety. The data shed tentative light on the possible complex mechanism that exist between gratitude, sleep, and psychological distress.

In line with existing data (Wood et al., 2008), chronic pain patients in this study with higher gratitude reported better sleep but lower depression and anxiety. Our data extended previous data that gratitude influences patients’ sleep quality which in turn affects their psychological well-being (Emmons and McCullough, 2003; Wood et al., 2008). Specifically, the indirect effect of sleep on the gratitude–depression link was 0.02, suggesting that approximately 10.5% of the effect of gratitude on depression went through the mediating factor, sleep, while up to 89.5% of the effect was direct. The indirect effect of sleep on the gratitude–anxiety link was 0.05, suggesting that about 45.5% of the effect of the gratitude on anxiety was carried through sleep and about 54.5% was direct. These interesting findings suggest that, while improved sleep exerted a much stronger indirect mediating effect on the gratitude–anxiety link, trait gratitude demonstrated a stronger direct effect on depression, with only 10.5% of the effects went through sleep. Considering the mediating effect alone, sleep had a higher practical value when considered as a mediator in the gratitude–depression link given the higher indirect effect it carried in Model 1. The higher z-score in Model 1 also contributed higher precision than Model 2 in explaining the variance of the gratitude–sleep–distress link. These data imply that different underlying mechanisms may exist for explaining how gratitude and sleep impact depression and anxiety. The direct effect of gratitude on depression may be associated with more general, stable positive cognitions, such as life evaluations and perceptions of social support (Emmons and McCullough, 2003) held by grateful individuals. Higher positive but lower negative pre-sleep cognitive may be the underlying process explaining the mediating role of sleep in the gratitude–anxiety link (Wood et al., 2009). Apparently, the link between the three variables may not be through a simple linear path, but possibly through a more complex mechanism that includes other mediating factors. This awaits future elucidation.

In line with previous studies (Tang et al., 2007; Wong et al., 2011), our data showed chronic pain patients with insomnia reported significantly more pain sites, higher pain intensity and interferences, and pain-associated disability. Pain and insomnia probably mutually reinforce each other and five hypotheses have been formulated to explain the possible underlying mechanisms: first, the neurobiological perspective suggested that an increase in sensitivity of the neuro-anatomical pathways of nociception among patients with chronic pain interferes with the ability to initiate and maintain sleep which may increase emotional arousal, thereby compounding the problem (Parker et al., 2001); second, pain medication disrupts the sleep–wake cycle (Stiefel and Stagno, 2004); third, chronic pain and depression share a common pathophysiology of serotonin deficiency that influences sleep (Brown, 1990); fourth, the link between sleep problems and psychological distress may be mediated by increased health-related anxiety and heightened bodily sensation (Asmundson et al., 2000). Finally, when there is bodily discomfort, this makes sleep difficult as movement may elicit pain sensation, which can disturb sleep. More research is needed to clarify which of these is most likely.

Our data are limited by the cross-sectional nature, limiting etiological inference and causality. Caution is therefore warranted in interpreting and generalizing the current findings in other populations and contexts. The results of t-tests and chi-square tests should also be interpreted in light of the possible inflated Type 1 errors. Apart from the sociodemographic and pain variables assessed, other potentially influential psychosocial and clinical factors, such as pain diagnosis and previous/concurrent medical services sought, were not assessed in this study. Future research that employs more rigorous design (e.g. longitudinal, prospective design) and analytical approach (e.g. structural equation modeling) is needed to delineate the causal association of gratitude, sleep, and psychological distress and their underlying mechanism in other populations and cultures.

Despite these limitations, our data offer preliminary evidence for the mediating role of sleep in the relationship of gratitude with psychological distress. Previous studies have shown that gratitude intervention that applied in organizational, education, and healthcare settings, improved the psychological well-being of people in different age groups and with different religious backgrounds (Childre and Cryer, 2000; Childre and Martin, 1999). Since psychological distress has been shown to hamper the management of chronic pain (Harter et al., 2002; Jensen et al., 2006), future research may explore the possibility of applying gratitude intervention in chronic pain populations, examining whether it would improve the overall efficacy of a multidisciplinary pain management program.

Footnotes

Acknowledgements

Part of the data presented in this article is based on the dissertation submitted by the first author (MY Ng) under the supervision of the corresponding author (WS Wong) in partial fulfillment of the requirements for the Bachelor of Social Sciences in Psychology degree in the Department of Applied Social Studies, City University of Hong Kong.

Competing Interests

None declared.

Notes

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