Writing in the journal Sleep, the authors say that round-the-clock entertainment, commuting, shift work and family responsibilities have all contributed to a sleep-deprived society. For instance, in the 1960s sleep duration was estimated to be approximately eight hours a night, whereas by 2005 this had fallen to seven hours or less.
They say that lack of sleep poses a range of health problems, but one that is gaining more credibility is the way it increases peoples' sensitivity to pain.
To test this relationship between sleep and pain, the researchers from Detroit recruited 18 healthy, pain-free volunteers and randomly assigned them to two groups during an experiment lasting four nights. Those in one group stuck to their normal sleep routines while the adults in the other group got more sleep by spending 10 hours in bed each night.
Testing pain response
All the volunteers had their daytime sleepiness assessed using the multiple sleep latency test (MSLT), which monitors how long it takes a person to fall asleep if given the opportunity to snooze during the day. Sensitivity to pain was measured by noting how long it takes a person to pull their finger away from a heat source they cannot see.
Results show that those in the extended sleep group slept 1.8 hours more each night than those who maintained their normal sleeping habits. The longer sleepers were not only more alert during the day but were also less sensitive to pain.
In the extended sleep group, the length of time before volunteers removed their finger from a radiant heat source increased by 25%, reflecting a reduction in pain sensitivity. The authors report that the magnitude of this increase in the time it took to pull their finger away was greater than the effect found in a previous study in which volunteers were given 60 mg of the painkiller codeine.
Could it help patients?
"Our results suggest the importance of adequate sleep in various chronic pain conditions or in preparation for elective surgical procedures," says Timothy Roehrs, the study's lead author in a statement. "We were surprised by the magnitude of the reduction in pain sensitivity, when compared to the reduction produced by taking codeine."
Exactly how more sleep can help improve pain is not fully understood. "We think that sleep loss and pain both increase levels of inflammatory markers, but getting more sleep may help decrease this inflammation," says co-researcher Thomas Roth who is director of a sleep disorder centre in Detroit.
According to the authors, this is the first study to show that extended sleep in mildly, chronically sleep deprived volunteers reduces their pain sensitivity. One expert in the UK tells us that sleep and pain have been the subject of previous research. "Work at Harvard has explored the effect of sleep deprivation on pain perception and found that the threshold for pain perception is reduced under those circumstance," says Adrian Williams, professor of sleep medicine at King's College London.
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