Have you ever wondered why you hurt especially at night unlike in the afternoon? French researchers have found the answer. Pain intensity is controlled by the internal clock, peaking at 3am. Ouch
Boost your sleep to reduce your ailments? Pain, a fortiori when it is chronic, can be truly debilitating and have a negative impact on the days of the people concerned… but also their nights. Yes, because it is at three o’clock in the morning that it reaches its climax. This has just been highlighted by researchers from Inserm (National Institute for Health and Medical Research) who have published their research in the scientific journal Brain July 20, 2022 (in English, link below) *. This discovery could lead to new approaches for the treatment of pain.
Minimal pain between 3 and 4 p.m.
The level of activity of many bodily functions is regulated by the circadian rhythm, a kind of internal clock set on a 24-hour cycle; this concerns the sleep/wake system, body temperature, blood pressure, hormone production, heart rate, but also cognitive abilities, mood and memory. Pain is now added to this long list. If its maximum intensity is between three and four o’clock in the morning, twelve hours later (between three and four o’clock) it reaches its lowest level, and this ” regardless of behavior and any external factors in the environment “, underline the researchers.
12 young people awake for 34 hours
To highlight this, they studied twelve young adults in the laboratory under conditions “ temporal isolation and constant routine. They kept them awake for 34 hours without any external signal or environmental rhythm reaching them: no schedule, no meal at a fixed time but a snack every hour, constant temperature and low light, no change of posture (semi-lying position) and no activity/rest rhythm. The team then exposed the participants’ forearms to a heat source every two hours, who had to indicate when the stimulus became painful and then rate the intensity of the pain on a scale of 1 to 10 during the application of a temperature of 42, 44 or 46 degrees Celsius. ” The results are very homogeneous with an association (note: between internal clock and pain) extremely significant “says Claude Gronfier, one of the authors of the study.
Less sleep, more pain
First conclusion: sensitivity to pain increases linearly with sleep debt, which corresponds to a sleep time lower than required. In other words, the greater the sleep debt, the greater the intensity of the pain felt. ” It is often said that sleep has an analgesic action. But, by mathematically modeling our results, we show that the internal clock is responsible for 80% of the variation in pain sensation over 24 hours, compared to only 20% for sleep. », Clarifies Claude Gronfier. Why ? ” We can think that evolution has put this in place in order to be awakened quickly in the event of painful contact and to avoid a vital threat. During the day, the individual is aware of the surroundings and more easily prone to injury; this warning signal could therefore be less necessary “, he supposes.
Consider biological rhythms
For Claude Gronfier, it is therefore legitimate to think ” that improving the synchronization of biological rhythms and/or the quality of sleep in individuals suffering from chronic pain could contribute to better therapeutic management “. In addition, ” just as chronotherapy of cancer has proven itself with better efficacy and reduced toxicity when drugs are administered at certain times of the day, adapting an analgesic treatment according to the same process, taking into account the biological rhythm of each person, could increase its effectiveness while reducing the necessary dose and potential adverse effects “, he adds. However, this hypothesis remains to be validated by clinical trials before being able to offer this chronobiological approach to patients… When will the verdict be announced? Tick, tock, the clock is ticking!
* within the Lyon Neuroscience Research Center (Inserm/Claude Bernard Lyon 1 University/CNRS)
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