BALTIMORE -- Sleep disturbance may set up a vicious cycle of spontaneous and chronic pain, which in turn can contribute to sleep loss, according to a study by Johns Hopkins University.

In a seven-night sleep study, women who were forced awake every hour of the night -- say, by a new baby -- lost pain inhibition and had significantly more spontaneous pain than those whose sleep schedules were shortened or those who got a full eight hours, found Dr. Michael T. Smith of Johns Hopkins, and colleagues.

People who suffer from night-time awakenings and those who have fragmented sleep -- such as firefighters, on-call medical personnel, or parents of infants -- have alterations in the natural systems that regulate pain and keep it in check, Smith and colleagues noted.

Interrupted sleep appears to adversely affect central pain modulation, with a commensurate increase in spontaneous pain, they said.