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A 24-hour rhythmicity of pain: peak and trough times

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Like many body functions, pain intensity is controlled by the internal circadian clock, shows a French study published in July 2022 in the journal Brain.

She shows that this intensity (sensitivity) “oscillates over 24 hours with a peak at night and a fall in the afternoon independently of any external stimulation and the sleep-wake cycle.»

This discovery could lead to new approaches for the treatment of pain“, underlines the press release from the Inserm researchers.

The level of activity of many body functions is regulated by an internal clock set to a rhythm of about 24 hours: the sleep/wake system, body temperature, blood pressure, hormone production, frequency cardiac, but also cognitive abilities, mood or even memory.Added to this list is pain, the new study shows.

Claude Gronfier, researcher at the Lyon Neuroscience Research Center (Inserm) and his colleagues (1) conducted this study with twelve young adults in the laboratory under conditions of temporal isolation and constant routine. “They kept them awake for 34 hours without any external cues or environmental rhythms reaching them: no schedule, no fixed meal time but a snack every hour, constant temperature and low light, no change in posture (semi-lying position) and no activity/rest rhythm.»

Participants, whose forearm was exposed to a heat source every two hours, were asked when the stimulus became painful as the temperature increased as well as the intensity of the pain on a scale of 1 to 10 when applying a temperature of 42, 44 or 46 degrees Celsius.

A variation over 24 hours

In all participants, a rhythmicity of pain sensation was observed over the 24 hours. “The results are very homogeneous with an extremely significant association“says Claude Gronfier.

The intensity of the pain varied over 24 hours with a maximum intensity between 3 and 4 a.m. and minimum around 3 and 4 p.m. in the afternoon, independently of behavior and of any external environmental factor.

As previous works suggested without having demonstrated it,pain sensitivity increased linearly with sleep debt: 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 the researcher. (How Sleep Influences Pain Sensitivity)

This circadian variation in pain certainly has a physiological utility, the researcher believes. “It is not known why sensitivity is highest in the middle of the night. 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.»

This discovery is part of the concept of personalized medicine, and more precisely of circadian medicine. This is emerging and takes biological rhythms into account in the care of patients.“, Underlines the press release from Inserm.

It is 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.“says the researcher.

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 individual, could increase its effectiveness while reducing the necessary dose and the potential adverse effects.» (Chronotherapy that takes biological rhythms into account improves cancer treatment)

But this hypothesis remains to be validated by clinical trials before being able to offer this chronobiological approach to patients.“, he warns.

For more information, see the links below.

(1) Inès Daguet, Véronique Raverot, Didier Bouhassira.

Psychomedia with sources: Inserm, Brain.
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