Losing sleep can lead to increased pain sensitivity, study suggests

Chronic sleep loss leads to increased pain sensitivity and ever larger doses of painkillers are needed in order to deal with the discomfort, a new Harvard study on mice revealed. Doctors infer that if the results are also true for humans, patients dealing with chronic pain could benefit from better sleeping patterns.

It could be said that in modern times, sleep deficiency has grown to epidemic proportions. In the United States alone, the CDC predicts that one in three adults is not getting enough sleep on a regular basis. Sleep problems, including insomnia, obstructive sleep apnea, restless legs syndrome and sleep deprivation in general, affect up to 45% of the world’s population, the World Association of Sleep Medicine estimated back in 2011.

Since then, several studies have suggested that adults are not the only ones affected by sleep deficiency. A Standford research  concludes that in industrialized nations, sleep deprivation among teens has become acute and needs to be urgently addressed.

And while research into the myriad of negative consequences that sleep deprivation has on the human body is still in its infancy; the inability to concentrate, drowsiness, stress, anxiety, depression are all well-documented side effects with one more addition, increased pain sensitivity, new study suggests.

Less sleep, more pain

Scientists form Harvard Medical School, together with researchers at Boston Children’s Hospital and Beth Israel Deaconess Medical Center conducted experiments in order to see how sleep deprivation affects pain sensitivity.

Pain physiologist Alban Latremoliere, HMS research fellow in neurology at Boston Children’s, and sleep physiologist Chloe Alexandre, HMS instructor in neurology at Beth Israel Deaconess, who were co-first authors of the study, precisely measured the effects of acute or chronic sleep loss on sleepiness and sensitivity to both painful and nonpainful stimuli. They then tested standard pain medications such as ibuprofen and morphine, as well as wakefulness-promoting agents like caffeine and modafinil.

Practically, after keeping mice awake by engaging them in entertaining activities, the scientists measured their reaction to painful stimuli like heat, pressure and capsaicin, the substance in hot chilli peppers. The researchers also tested responses to nonpainful stimuli, such as jumping when startled by a sudden loud sound.

“We found that five consecutive days of moderate sleep deprivation can significantly exacerbate pain sensitivity over time in otherwise healthy mice,” said Chloe Alexandre. “The response was specific to pain, and was not due to a state of general hyperexcitability to any stimuli.”

When they wanted to measure how pain medication fared with the new sensitivity, scientists found that common painkillers such as ibuprofen did not block the pain hypersensitivity induced by sleep loss. Even morphine lost most of its efficacy in sleep-deprived mice.

Better sleeping patterns could help patients

If these results are replicated in humans, that means that patients with chronic sleep loss will have to take ever larger doses of painkillers in order to manage their pain.

On the other hand, caffeine and modafinil, drugs used to promote wakefulness, successfully blocked the pain hypersensitivity caused by both acute and chronic sleep loss. In non-sleep-deprived mice, caffeine and modafinil had no painkilling properties.

“This represents a new kind of analgesic that hadn’t been considered before, one that depends on the biological state of the animal,” said Woolf, director of the F.M. Kirby Neurobiology Center at Boston Children’s. “Such drugs could help disrupt the chronic pain cycle, in which pain disrupts sleep, which then promotes pain, which further disrupts sleep.”

Thanks to collaboration, the scientists, together with Thomas Scammell, HMS professor of neurology at Beth Israel Deaconess, were able to make some surprising discoveries when it comes to the role alertness plays in pain sensitivity. The findings could help doctors better manage patients suffering from chronic pain.

“This cross-disciplinary collaboration enabled our labs to discover unsuspected links between sleep and pain, with actionable clinical implications for improving pain management,” Scammell said.

Instead of just taking pain medicine, patients with chronic pain could benefit from better sleep patterns. They could be given sleep-promoting medicine at night and during the day they could be prescribed alertness promoting substances. And some painkillers already contain caffeine as an ingredient and the effects that both caffeine and modafinil have on pain could be explained by the fact that the substances boost dopamine circuits in the brain.

Scientists are saying that further research and testing is needed in order to understand the complex relationship between pain sensitivity, sleeping deficiency and common painkillers in order to provide better care for suffering patients.