Poor sleep quality has a deleterious impact on individuals’ physical and mental health, occupational functioning, and overall quality of life [27
]. Of particular relevance here, research involving clinical samples and healthy individuals exposed to controlled laboratory stimuli has documented reliable relations between poor sleep and increased pain severity [28
]. However, the association between sleep quality and psychosocial contributors (e.g., pain catastrophizing) to negative pain outcomes has not received much attention and remains unclear. Catastrophizing is a known psychosocial contributor to worsened pain outcomes, and it has been suggested that African Americans engage in greater pain catastrophizing compared to Caucasians [9
]. As such, an examination of the relation between sleep quality and pain catastrophizing should consider ethnicity. This is because ethnicity has previously been shown to interact with sleep habits in relation to a host of clinical outcomes including blood pressure [30
], catecholamine levels [31
], and health-related quality of life [32
]. Furthermore, in a study investigating sleep architecture, polysomnography revealed that African Americans experienced the greatest amount of non-restorative sleep, characterized by poor sleep efficiency, frequent awakenings, and little slow wave (delta) sleep, relative to other ethnic groups [33
]. Taken together, it is plausible that ethnicity could interact with sleep quality in relation to pain catastrophizing and other pain-relevant outcomes. The purpose of this study was to address the interaction of ethnicity with sleep quality in relation to reports of standard and situation-specific pain catastrophizing in a multi-ethnic sample of young, healthy adults exposed to the cold pressor task.
Ethnic differences in the standard measure of pain catastrophizing were only significant for those who self-reported as “poor sleepers”. Among individuals with poor sleep quality, African Americans produced the greatest reports of standard catastrophizing when compared to Asian and Caucasian Americans, who did not differ from each other. Ethnic differences in standard catastrophizing were not significant for “good sleepers”. These findings provide one potential explanation for why some studies have found ethnic differences in catastrophizing [12
], while others have not [10
]. Ethnic differences in pain catastrophizing may be dampened when the sample is comprised of participants who sleep well, yet ethnic differences in catastrophizing may be potentiated when the sample is comprised of poorly sleeping participants. It should be mentioned that a particular strength of the current study is the inclusion of three separate ethnic groups. The majority of studies that have previously investigated ethnic differences in health-related outcomes only examined African Americans and Caucasian Americans. The finding that Asian Americans with poor sleep quality did not self-report greater standard or situation-specific pain catastrophizing compared to Caucasian Americans is novel and is deserving of further exploration. Future studies should more specifically examine whether African Americans in particular, rather than minority groups in general, may be susceptible to the ill effects of poor sleep quality on pain coping strategies.
Support was not provided for the interactive effect of ethnicity by PSQI Global sleep quality in relation to situation-specific measure of pain catastrophizing. While the reason(s) for the differences in relational patterns among ethnicity and sleep quality with standard and situation-specific catastrophizing is not abundantly clear, it may be that results vary as a function of catastrophizing assessment. Previous studies have shown that standard and situation-specific assessments of catastrophizing yield somewhat different information [34
]. Therefore, the interaction between sleep quality and ethnicity may differently relate to catastrophizing as a function of situation-specific measurement (i.e., degree of catastrophizing in a specific painful situation) as opposed to standard measurement (i.e., a person’s general tendency to catastrophize when in pain). Despite the lack of an interactive effect between PSQI Global sleep quality and ethnicity in relation to situation-specific catastrophizing, additional analyses revealed that habitual sleep efficiency did significantly interact with ethnicity to affect situation-specific catastrophizing reports. Previous studies have confirmed the importance of sleep efficiency as an important sleep quality parameter in relation to pain [35
]. Among those with poor sleep efficiency(i.e., </= 85%), African Americans reported elevated situational catastrophizing scores relative to Asian and Caucasian Americans; there was no significant difference between the latter two ethnic cohorts. Among those individuals with habitual sleep efficiency > 85%, no ethnic differences in situation-specific pain catastrophizing were demonstrated.
It is important to note that, in the present study, mean PSQI Global sleep quality scores were not significantly different across the three ethnic groups. This may be interpreted such that sleep quality did not directly differ as a function of individuals’ ethnic background. However, significantly elevated pain catastrophizing reports were found for poorly sleeping African Americans compared to their poorly sleeping Caucasian and Asian American counterparts. These findings suggest that individual differences in subjective sleep quality contribute to variability in the report of pain catastrophizing within the African American group, and that this association is less robust among Caucasian and Asian Americans (e.g., although individual differences exist among Caucasian and Asian Americans in their sleep quality, this variability is less influential on their reports of pain catastrophizing). Ethnicity and sleep quality also did not significantly interact in relation to CPT-induced pain reports or pain tolerance; however, both standard and situation-specific measures of catastrophizing were correlated with pain tolerance and ratings of pain intensity and unpleasantness. These results may indirectly support the ability of the sleep quality-ethnicity interaction to affect pain reports through pain catastrophizing processes; however, additional studies are necessary to confirm this hypothesis.
It should be noted that this cross-sectional study, with observational data, was not designed to demonstrate causal relations; however, it does preliminarily relate poor sleep quality with heightened pain catastrophizing and suggests that this relation varies as a function of self-reported ethnic background. The current study does not rule out the possibility that the associations among ethnicity, poor sleep quality, and pain catastrophizing may be bidirectional or co-occurring. That is, African Americans who express greater catastrophizing in relation to daily aches and pains may prime themselves for a poor night’s sleep, which in turn could elicit self-reports of poorer sleep quality. Another potential factor affecting the pattern of the sleep quality-pain catastrophizing relation might be whether the painful stimulation experienced is acute or chronic. For instance, in a sample of healthy, pain-free individuals, there may be a greater likelihood for poor sleep quality to influence catastrophizing about a single, acutely painful stimulus. Conversely, in a clinical sample of individuals afflicted with a painful condition, chronic rumination and feelings of helplessness characteristic of catastrophizing may be more likely to negatively impact sleep quality over time. This assertion is speculative and extends beyond well-accepted fact. Therefore, the explanation may be plausible but evidence supporting this explanation is currently lacking.
The current study’s findings call for consideration to be given to sleep and catastrophizing as potential treatment targets when treating painful conditions among African Americans. Addressing sleep quality may have a beneficial effect on African American’s pain experience or their perceptions regarding their ability to cope with their pain. Current evidence supports cognitive-behavioral therapies (CBT) for the effective treatment of chronic pain [37
], and demonstrates improvements in pain, mood, coping and functional outcomes [38
]. These approaches have more recently begun to address pain catastrophizing [40
], but may not regularly incorporate assessment or treatment of sleep as a treatment module. Whether improvements in pain catastrophizing can be produced by improving African American’s sleep quality remains unknown and is a point for future investigation. Results of this study suggest that pain catastrophizing should continue to be a regular component of CBT for pain, but that sleep should also be included in treatment approaches, particularly among African Americans.
The present study possesses several limitations and qualifications that merit caution when interpreting the findings. First, study participants self-reported their ethnic background using relatively broad categories; further subdivision of individuals’ perceived ethnicities and cultural backgrounds may provide additional valuable information. Another limitation is that all study participants were college students, and college students have previously been shown to regularly maintain atypical sleep habits [42
]. As a consequence, the generalizability of these findings is not perfectly clear and replication of these effects in other samples will be quite pertinent. Given that sleep deficits and catastrophizing are typically higher and more variable in clinical pain [1
], the associations among ethnicity, sleep quality, and pain catastrophizing may well be stronger in clinical populations than was found in our non-clinical sample. Lastly, in the present study, sleep quality was subjectively reported using the Pittsburgh Sleep Quality Index. Although the PSQI is largely considered the gold standard for the self-report of sleep quality, future studies would benefit from a multimethod approach to sleep assessment that includes objectively derived sleep parameters (e.g., via polysomnography and actigraphy). Such assessment would allow for enhanced understanding of how specific domains of sleep quality (e.g., waking after sleep onset, latency, and sleep duration) may affect pain coping processes. In spite of these limitations, our findings identify self-reported sleep quality as a potentially important and previously unattended factor related to individual differences in the report of pain catastrophizing among African Americans. Continued investigation of ethnic differences in pain coping strategies, and the mechanisms underlying them, appears warranted. Researchers studying sleep in ethnic minority groups may wish to examine whether cognitive-behavioral treatments that improve sleep quality produce concomitant improvements in pain catastrophizing processes as a function of improved sleep.