Timothy Roehrs of Henry Ford Hospital in Detroit said the study he led involved 18 healthy, pain-free, sleepy volunteers. They were randomly assigned to four nights of either maintaining their habitual sleep time or extending their sleep time by spending 10 hours in bed per night.
Daytime sleepiness was measured using the multiple sleep latency test and pain sensitivity was assessed using a radiant heat stimulus.
The study, published in the December issue of the journal Sleep, found the extended sleep group slept 1.8 hours more per night than the habitual sleep group and this extra sleep was correlated with greater daytime alertness, which was associated with less pain sensitivity.
"Our results suggest the importance of adequate sleep in various chronic pain conditions or in preparation for elective surgical procedures," Roehrs said in a statement. "We were surprised by the magnitude of the reduction in pain sensitivity, when compared to the reduction produced by taking codeine."