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Emerging research trends on the relationship between sleep and pain

Emerging research trends on the relationship between sleep and pain

The relationship between pain and sleep quality is well reported in the literature. Sleep complaints are present in up to 88% of chronic pain disorders and at least 50% of patients presenting with insomnia also suffer chronic pain. This article focusses on a recent review by Finan, Goodin and Smith(2013) who aimed to identify emerging trends in the relationship between pain and sleep, particularly those involving chronic pain patients. The main themes for the review include the possible mechanisms involved and the direction of causality in the relationship.

The mechanisms connecting sleep characteristics and pain perception are unsurprisingly complex. Sleep restriction is associated with attenuated cortical activity in the insular and cingulate regions suggesting that the hyperalgesic effects of partial sleep deprivation is mediated by impairments in the descending modulatory systems, rather than an amplification of the ascending sensory pathways. Dopaminergic signalling also may play an important role in contributing to sleep deficits seen in chronic pain sufferers. The mesolimbic system releases dopamine in the maintenance of arousal states which is involved in sleep modulation. This suggests that chronic pain that also disturbs sleep, could further lead to dysregulation of the sleep-wake cycle.

From a day to day perspective, the temporal effect of sleep on pain may be stronger than that of pain on sleep. Experimental studies outlined in the review indicate that sleep disturbance has a substantial effect on pain perception as chronic sleep deprivation and was likely to correlate with increased pain sensitivity, and further, that extended sleep within the same population promoted reduced pain sensitivity. From a clinical standpoint, addressing sleep quality deficits may be worthwhile in the efforts to treat and prevent chronic pain. This view is further supported by findings that reduced sleep efficiency also reduces the efficacy of analgesics used in chronic pain patients, in particular, the use of endogenous opioid-mediated pain inhibition

In prospective studies, which followed participants for over a year, the incidence of insomnia was a significant predictor of migraine in Danish and Norwegian populations. Similarly, a sleep disorder or difficulties falling asleep were significant predictors of fibromyalgia in Norwegian women. These findings not only lead to changes in how pain and sleep research is carried out, but further move the aim of research from exploring whether pain and sleep are associated, to how pain and sleep are associated.

Research on the contribution of mood to the relationship between pain and sleep quality was also explored. Sleep, pain and the influence of positive or negative affect have been shown to be related; however various methodologies and the lack of any identifiable antecedent in the mood-sleep-pain pathway make the drawing of conclusions difficult. For example, one study explored how negative mood altered the relationship between sleep and pain, whereas another explored how sleep mediated pain and depression. A further study looked into how treating depression with pharmaceuticals might affect the interaction between pain and sleep, though no attenuation in self-reported pain and sleep was reported.

To conclude, recent studies indicate that sleep impairment is a predictor of future incidents of chronic pain and that sleep deficits are a stronger, more reliable predictor of pain than pain is of sleep deficits. Further directions suggested by Finan, Goodin and Smith (2013) include looking at the effects of socio-demographic factors on pain and sleep, including sex, age, race, income, etc. and an increased focus on partial sleep restriction designed studies as they are more likely to simulate the effects of common sleep problems on pain sensitivity. Lastly, Finan, Goodin and Smith (2013) suggest additional research into how different chronic pain conditions are affected by changes in sleep, which may give further insight into the mechanisms involved, for example, how chronic pain is affected by forced wakefulness or fragmented sleep.

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