We feel more pain at night, here’s why – Edition du soir Ouest-France

Friday, September 16, 2022


Human beings would be more sensitive to pain in the middle of the night rather than in the middle of the afternoon. French scientists point the finger at the culprit: the circadian rhythm, our body’s internal clock. Explanations.

Have you ever felt like your headache or toothache intensified when you were desperately trying to sleep at night? A French scientific study published on September 9, 2022 in the journal Brain and directed by Claude Gronfier, from the Center for Neuroscience Research in Lyon, has come to the end of this mystery. It wasn’t a figment of your imagination: our sensitivity to pain fluctuates throughout the day and night. This evolution would be linked to our circadian rhythm, the internal clock of the human body. More precisely, it is a biological rhythm of a cycle of approximately 24 hours which governs the functioning of our metabolism and influences all the systems of our organism such as sleep and food.

Read also: The US Army technique to fall asleep in 2 minutes flat

The study reveals that we are most sensitive to pain between 3 a.m. and 4:30 a.m. in the middle of the night, and least sensitive around 3 p.m. So avoid banging your toe on the corner of your table at this hour… Another discovery? Sleep deprivation has a much weaker influence on pain sensitivity than researchers previously thought. The French scientists noted that the increase in this receptivity caused by the lack of sleep would intensify slowly, little by little, during the night.

Result: our susceptibility to pain is 80% due to our biological clock and 20% to a lack of sleep. “We were surprised by this ratio. Indeed, I thought we would have a lot more sleep drivessaid Claude Gronfier the director of the study according to the American magazine Wired . But that doesn’t mean sleep isn’t important, as we conducted our study in very good sleepers. »

A cycle of pain

To come to the end of this existential question, the four French researchers recruited twelve men, young men in good health and free from sleep disorders, who agreed to submit to a strict protocol for 34 hours. A period during which they were deprived of their watch, smartphone and sunlight, or any element serving as time markers.

During this time, the team assessed their sensitivity to pain, every two hours, using a device placed on the forearm whose temperature slowly increased until the individuals reported their pain. A cycle of pain arose: on average, tenderness peaked between 3 and 4 a.m., before reaching its lowest point about twelve hours later.

Read also: Can the brain feel pain?

A study without women to limit disturbances linked to the menstrual cycle

The downside of this study? The laboratory conditions were too perfect. The sleep of the participants had been regulated before the experiment whereas the “lack of sleep is common in our society”, the attendees were “healthy”, without pain or sleep disorders… To confirm the researchers’ hypothesis, this study should be repeated in real life conditions and on heterogeneous individuals. Including women. They had been excluded to limit disturbances linked to the menstrual cycle.

We see gender differences whenever we do something with men and womenDebra Skene, a circadian rhythm biologist at the University of Surrey in England, who was not involved in the research, told Wired. But for me, I think it would be about the amplitude [l’intensité de la douleur], I don’t think it’s going to change when we’re most sensitive. »

Another important limitation of this study? It relates only to a particular pain, the burning sensation. “We cannot assume that [ces résultats] will show that all types of pain peak at night,” reports the study.

But this discovery could still be a breakthrough for medicine. Pain treatment could be optimized by keeping pace with the patient’s internal clock rather than that of the hospital room!

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