Lower threshold for physical discomfort
The more frequent and severe the insomnia, the greater the sensitivity to pain, the Norwegian study showed. Additionally, the researchers noted that people with insomnia who also suffer from chronic pain have an even lower threshold for physical discomfort.
It's important to note, however, that while the study found an association between a lack of quality sleep and increased pain sensitivity, it wasn't designed to show a cause-and-effect relationship.
The study, led by Borge Sivertsen, of the Norwegian Institute of Public Health in Bergen, involved more than 10,000 adults. The study participants all underwent a standard test of pain sensitivity by dunking their hands in a bath of cold water for 106 seconds.
The volunteers were also asked about their sleep quality. Specifically, they were questioned about insomnia, how long they slept and how long it took them to fall asleep. The researchers also took into account other factors that might affect pain tolerance, such as recurring pain, depression and anxiety.
They found that nearly one-third of participants were able to keep their hand in the cold water for the entire test.
Those with insomnia, however, were more likely to remove their hand from the water early. In fact 42 percent of people with insomnia pulled their hand out before the test ended, compared to 31 percent of those without this sleep disorder, the study published in the journal PAIN revealed.
Tolerance of pain drops with sleep quality
People with more severe cases of insomnia had greater pain sensitivity, suggesting tolerance of pain drops along with sleep quality.
For example, rates of reduced pain tolerance were 52 percent higher for subjects with insomnia that occurred more than once a week compared to those who didn't have insomnia.
Meanwhile, rates of reduced pain tolerance were just 24 percent higher for those who had insomnia once a month, according to the study.
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People with insomnia and chronic pain were more than twice as likely to have reduced tolerance to pain, the research revealed.
"While there is clearly a strong relationship between pain and sleep, such that insomnia increases both the likelihood and severity of clinical pain," Sivertsen and his co-authors wrote, "it is not clear exactly why this is the case."
The study also suggests that psychological factors may play a role in the association between poor sleep and pain. Also, more research is needed to investigate how neurotransmitters, such as dopamine, could affect pain and sleep, the researchers said.
Image: Woman with insomnia from Shutterstock