A recent study published in PAIN, the official journal of the International Association for the Study of Pain, shows that individuals with insomnia or other sleep problems have increased pain sensitivity. Wei Zhang, Department of Psychiatry, Shijiazhuang Eighth Hospital Co-morbid insomnia and chronic pain can severely affect an individual’s pain tolerance, and such patients may benefit from measures to treat both symptoms. The study was led by Dr. B?rge Sivertsen of the Norwegian Institute of Public Health. Increased pain sensitivity in individuals with insomnia 10,400 participants from a large Norwegian health study. Each participant underwent a standard pain sensitivity test, the cold pressor test (a test in which subjects are asked to immerse their hands in a cold water bath). The researchers investigated various types of sleep impairments present in the participants, including: insomnia, total hours of sleep, and sleep latency (the time it takes to go to sleep); ultimately analyzing the relationship between sleep impairments and pain sensitivity. The study also investigated other factors that may affect sleep and pain perception, including chronic (persistent or recurrent) pain and psychological distress (e.g., depression, anxiety). Thirty-two percent of participants could keep their hands immersed in cold water throughout the 106 seconds of the test. Insomniacs (42%) were more likely to be unable to tolerate it and take their hands out earlier; 31% of those without insomnia symptoms. Nociceptive sensitivity increased with the frequency and severity of insomnia; for example, the rate of decrease in nociceptive sensitivity compared with those without insomnia symptoms was 52% higher in those with insomnia more than once a week than in those with insomnia once a month (24%). Nociceptive sensitivity was also associated with sleep latency, but not with total sleep hours. Correlations remained after adjusting for age and gender confounders; further adjustment for the effect of psychological distress resulted in a smaller but still relevant effect. Synergistic Effects of Sleep Problems and Chronic Pain There was also a strong joint (synergistic) effect of insomnia and chronic pain on nociceptive sensitivity. Individuals who self-reported having more severe insomnia with chronic pain were more than twice as likely to have reduced pain tolerance. “It is clear that there is a strong link between pain and sleep, such that insomnia simultaneously increases the risk and severity of clinical pain,” said co-author Dr. Sivertsen, “but at this point we don’t know why this happens.” This is the first study to find that insomnia and sleep impairment reduce pain tolerance in a general population sample. The findings suggest that psychological factors either partially contribute to the relationship between sleep problems and pain. More research is needed to explore the role of neurotransmitters in this, such as dopamine or which may affect both pain and sleep. In the meantime, this study makes clear the importance of working to improve the quality of sleep in chronic pain patients and vice versa. Cognitive-behavioral therapy has been shown to be effective in improving pain problems and insomnia, respectively, and Dr. Sivertsen and colleagues call on researchers to evaluate the role of early interventions in individuals who suffer from both insomnia and pain.