MONDAY, Dec. 3 (HealthDay News) -- Getting more sleep improves daytime alertness and reduces pain sensitivity in healthy adults, according to a small new study.

The research included 18 mildly sleep-deprived volunteers who spent four nights getting either their normal amount of sleep or extending their sleep time to 10 hours per night. The extended sleep group slept an average of 1.8 hours more per night than those in the normal sleep group.

Tests showed that the nightly increase in sleep time was associated with increased daytime alertness and less pain sensitivity.

The length of time that people in the extended sleep group were able to keep their finger on a heat source increased by 25 percent, the investigators found. That increase is greater than what was found in a previous study when participants took 60 milligrams of the painkiller codeine before undergoing the same pain sensitivity test.

The study, published in the December issue of the journal Sleep, is the first to show that extended sleep in mildly sleep-deprived people reduces their pain sensitivity, the researchers pointed out in a news release from the American Academy of Sleep Medicine. This and previous findings suggest that lack of sleep increases pain sensitivity.

"Our results suggest the importance of adequate sleep in various chronic pain conditions or in preparation for elective surgical procedures," study lead author Timothy Roehrs said in the news release. "We were surprised by the magnitude of the reduction in pain sensitivity, when compared to the reduction produced by taking codeine."

While the study found an association between extra sleep and reduced pain sensitivity, it did not prove a cause-and-effect relationship.

More information

The U.S. National Institute of Neurological Disorders and Stroke has more about sleep.