New research found that people with insomnia or other sleep disorders have increased sensitivity to pain.

Researchers found that the effect on pain tolerance appears strongest in people who suffer from both insomnia and chronic pain, who may benefit from treatments targeting both conditions. The study was led by Børge Sivertsen, PhD, of the Norwegian Institute of Public Health, Bergen.

For the study, researchers collected and analyzed data from more than 10,400 adults from a large, ongoing Norwegian health study. Each subject underwent a standard test of pain sensitivity--the cold pressor test--in which subjects are asked to keep their hand submerged in a cold water bath.

Subjects were asked about various types of sleep impairment, including insomnia, total sleep time, and sleep latency (time to falling asleep), and researchers assessed the relationships between measures of sleep impairment and pain sensitivity.

Overall, 32 percent of participants were able to keep their hand in the cold water throughout the 106-second test. Participants with insomnia were more likely to take their hand out early: 42 percent did so, compared with 31 percent of those without insomnia.

Pain sensitivity increased with both the frequency and severity of insomnia. For example, compared with individuals who reported no insomnia, rates of reduced pain tolerance were 52 percent higher for subjects reporting insomnia more than once weekly versus 24 percent for those with insomnia once monthly.

Pain sensitivity was also linked to sleep latency, although not to total sleep time. The relationships were unchanged after adjustment for age and sex. The effect was smaller, but still significant, after further adjustment for psychological distress.

The findings are detailed in the journal Pain.