People who suffer from insomnia and other sleep difficulties have greater sensitivity to pain, according to a new study published in the journal PAIN. The effects are strongest in those who suffer from both insomnia and chronic pain.
The study involved more than 10,400 adults from a large, ongoing Norwegian health study. Each participant underwent a standard test of pain sensitivity, known as the cold pressor test, in which they were asked to keep their hand submerged in a cold water bath.
Participants also reported on various types of sleep impairments, including insomnia, total sleep time, and sleep latency (time to falling asleep). Researchers assessed the relationships between measures of sleep impairment and pain sensitivity. They also investigated other factors that could potentially affect sleep impairment and pain perception, including chronic (persistent or recurring) pain and psychological distress (such as depression and anxiety).
Overall, 32 percent of participants were able to keep their hand in the cold water throughout the 106-second test. Subjects with insomnia, however, were more likely to take their hand out early: 42 percent did so, compared with 31 percent of those without insomnia.
The findings also showed that pain sensitivity increased with both the frequency and severity of insomnia. For example, 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 connected to sleep latency, but not to total sleep time. The link remained the same after adjustment for age and sex. The effect was smaller, but still significant, after further adjustment for psychological distress.
There was a strong combined effect of both insomnia and chronic pain on pain tolerance. Patients reporting high problems with both insomnia and chronic pain were more than twice as likely to have a lower pain tolerance.
This is the first study to link insomnia and impaired sleep to reduced pain tolerance in a large, general population sample. The findings suggest that psychological factors may contribute to the connection between sleep issues and pain, but they do not fully explain it.
“While there is clearly a strong relationship between pain and sleep, such that insomnia increases both the likelihood and severity of clinical pain, it is not clear exactly why this is the case,” writes study leader Børge Sivertsen, Ph.D., of the Norwegian Institute of Public Health, and co-authors.
More studies are needed to explore the role of neurotransmitters, such as dopamine, that may affect both pain and sleep.
Finally, the findings clearly show the need for efforts to improve sleep among patients with chronic pain and vice versa. Cognitive-behavioral therapies have been shown effective for pain problems and insomnia individually.
Source: Wolters Kluwer Health