Sleep – pain – sleep – pain – sleep
Today a client and I were discussing sleep. She said to me
‘Why is it that I can’t get off to sleep because I’m so sore, then I have a bad pain day, I’m really tired,
and I still can’t go off to sleep, so the next day I have a worse pain day.’

We’ve known anecdotally and in cross-sectional studies that people who have pain often have poor sleep, and when they have poor sleep, their pain gets worse… It seems to work in both directions!
And now, with a well-designed naturalistic study by Edwards and colleagues, we have some good data on the nature of this relationship.

The study was carried out in a national sample of nearly 1000 people who were not patients, but were recruited as part of another study of ‘midlife’. Most of the people were in their mid-40’s, roughly 50:50 male/female, mainly white (90%) and married (81%). For eight consecutive evenings, participants were telephoned, and asked about their sleep and pain ratings. Other information was also gathered, but what is of interest to us as clinicians, is the relationship between sleep and pain and sleep and pain over consecutive nights.

Now, as usual I’m not going anywhere near discussing the mathematics involved in structural equation modelling. One day I’ll blog about it, but not today. If you want to go into more detail yourself – go and read the article yourself. However, the findings were surprisingly clear: sleep predicted subsequent sleep, pain predicted subsequent pain, sleep predicted subsequent pain, pain predicted subsequent sleep.

The authors themselves state “significant effects of previous sleep on next-day pain, and of previous pain on subsequent sleep were found. Interestingly, the relationship was somewhat stronger for the prospective association of sleep with subsequent pain (Beta = .08, Zvalue = 7.9, p < .0001) compared to the prospective association of pain with later sleep (Beta = .04, Zvalue = 3.1, p = .002).”

What this means is that poor sleep predicted increased pain better than high pain predicting poor sleep, but there was a relationship between the two.

In terms of analysing the effect of yesterday’s pain on today’s pain – well, again the findings were quite interesting. The previous days’ pain was more predictive of today’s pain than age, BMI, comorbidities, an emotional disorder or using prescription medication.

Again, quoting the authors of this study, “The results of the present study suggest a significant curvilinear prospective association of sleep duration with subsequent daily pain report; individuals sleeping for less than 6 h, or for 9 h or more, reported more frequent pain complaints the following day. Evaluating the extremes of sleep duration, sleeping for three hours or less was associated with an 81% increase in pain frequency relative to sleeping 6–9 h, and sleeping for more than 11 h was associated with a 137% increase in pain frequency.”

Now that is pretty useful information. Remember that this is a normal, nonclinical population – these people don’t (yet) have persistent pain for which they are seeking treatment. It suggests that attending to poor sleep may be useful to

(1) screen for individuals who may be at risk of developing persistent problems associated with pain

(2) that poor sleep may be part of a group of symptoms that may need to be considered together when we develop new analgesics

(3) day-to-day fluctuations in sleep may be important to consider when evaluating patients in pain. If the person has had poor sleep for several days prior to an appointment, their pain report may be higher than ‘typical’ for them – and the sleep disturbance could be due to factors such as anxiety about the appointment, creating a vicious cycle.

(4) management of poor sleep may need to be the focus of non-pharmacologic pain management to help people cope better with their problem.

Remembering the usual proviso’s for non-experimental methodologies (and that there is maths and statistics involved!), and as the authors acknowledge, multidimensional measures of both sleep and pain would more accurately measure quality of sleep and pain rather than merely quantity, and most importantly, this study involved self report of sleep – which is notoriously unreliable – it is still clear that this study provides us with some food for thought.

And especially given that our clinical population so often complains of poor sleep – perhaps developing an increased awareness of non-pharmacological sleep management would be a good idea.

ABERNETHY, A. (2008). Pain and sleep: Establishing bi-directional association in a population-based sample☆. Pain, 137(1), 1-2. DOI: 10.1016/j.pain.2008.03.022

EDWARDS, R., ALMEIDA, D., KLICK, B., HAYTHORNTHWAITE, J., SMITH, M. (2008). Duration of sleep contributes to next-day pain report in the general population☆. Pain, 137(1), 202-207. DOI: 10.1016/j.pain.2008.01.025

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