Original ArticleSleep extension reduces pain sensitivity☆
Introduction
The existence of a ‘vicious circle’ relationship between insufficient sleep and pain sensitivity has been shown for a number of disorders including rheumatoid arthritis [1], fibromyalgia [2], [3]; and symptoms such as lower back pain [4] (reviewed in Ref. [5]). Likewise, it has been shown that sleep loss exacerbates pain sensitivity independently of pathology. In a large-scale study of more than 10,000 individuals in which the presence of pathology was controlled, self-reported sleep disturbances (eg, taking a long time to fall asleep, insomnia) were found to be a significant predictor of increased pain sensitivity [6].
In pain-free, healthy individuals total sleep deprivation has been shown to exacerbate self-reported pain measures [7], including (but not limited to) musculoskeletal tenderness [8], [9], as well as heat and cold sensitivity [10]. Likewise, chronic sleep restriction (ie, multiple days with less-than adequate sleep) has been found to reduce pain thresholds [11], [12] – effects that are reversed by recovery sleep (ie, extended sleep following sleep loss) [12], [13], [14]. However, to our knowledge, the effects of sleep extension (ie, increased nightly sleep durations relative to habitual, baseline sleep) on pain sensitivity have not been tested in healthy individuals.
Accordingly, in the present study we assessed the association between sleep extension and pain sensitivity (as measured on the Cold Pressor Task) within a healthy, pain-free non-sleep restricted sample of individuals with normal sleep habits. We hypothesized that sleep extension would improve pain sensitivity in non-sleep deprived individuals.
Section snippets
Participants
Twenty-eight healthy, pain-free volunteers participated in our study. Participants were recruited via flyers posted at local colleges, universities and military installations. The Institutional Review Board at the Walter Reed Army Institute of Research approved the study. Participants provided written informed consent and were compensated monetarily for their participation. Study participants first completed questionnaires to determine eligibility based on physical and psychological health; as
Results
Of the 27 individuals who participated, 17 were males. Average age was 24.41 years old (SD = 5.29, 19–39 years). Table 1 shows the general demographics of the sample. Sleep duration was significantly higher during the sleep extension phase (average 562.4 ± 32.9 min) than during five-day baseline (441.9 ± 60.8 min) and during the 10 days prior to the baseline period (455.1 ± 52.2 min). There were no differences in terms of sleep duration between the five-day baseline period and the 10 days
Discussion
The present findings indicate that sleep extension may result in increased pain tolerance in healthy individuals with normal sleep habits. Pain threshold, however, was not significantly affected by sleep extension. Additionally, individuals with a smaller sleep credit (ie, those who habitually obtain less sleep than they feel they need) realized greater increases in pain tolerance from sleep extension. Those with the greatest subjective habitual sleep debt might therefore obtain greatest
Conclusions
The present findings suggest that sleep extension may increase pain tolerance but not pain threshold in normal, healthy, young adults with normal sleep/wake schedules. Our findings also support the idea that sleeping in relation to the minimal subjective sleep requirement for adequate performance may be a strong indicator of sleep debt in the context of pain sensitivity. The implications of these preliminary findings are broad, and include, for example, the possibility that interventions to
Financial support
The Military Operational Medicine Research Program (MOMRP) from the U.S. Army Medical Research and Materiel Command supported this study.
Disclaimer
Material has been reviewed by the Walter Reed Army Institute of Research. There is no objection to its presentation and/or publication. The opinions or assertions contained herein are the private views of the author, and are not to be construed as official, or as reflecting the views of the Department of the Army or the Department of Defense. The investigators have adhered to the policies for protection of human subjects as prescribed in AR 70–25.
Acknowledgements
We would like to thank our technical staff and research participants that volunteered in this study. This manuscript was written while GS and JM held an NRC fellowship from the National Academies of Science, Engineering, and Medicine. We are grateful to the Military Operational Medicine Research Program from the U.S. Army Medical Research and Material Command for funding this study.
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All authors contributed significantly to this manuscript.