Are you dealing with pain? Is it cropping up more severely at different times of day?

A new study published in the Oxford Academic Journal digs deep into the phenomenon of pain: what it is, why it occurs, and why we feel it at varying degrees throughout the day.

The first step was to try and identify what pain is – something easier said than done due to its relatively nebulous existence.

“Pain is what we call a biopsychosocial experience,” Rocío de la Vega, a psychology researcher at the Biomedical Research Institute of Málaga and University of Málaga in Spain, told IFLScience. “It has elements that have to do with our bodies, and our brains… and [there’s] also a social dimension.”

De la Vega went on to explain that pain has a lot more to do with than tissue damage, and “a lot of times there’s no tissue damage or there’s no danger. Other things are in play, and more complex, multidisciplinary therapies are needed to tackle it.”

Basically, pain is an intensely personal experience and can be incredibly different to describe to others.

But, pain is also a critical survival mechanism, especially the acute pain that comes from trauma like an injury, a burn, or an accident. Pain works like an alarm signal to our brain.

“Our brain is telling us, ‘hey, be careful – something is wrong, stop touching that, or stop walking, because you’re going to get hurt,’” de la Vega explained. “So it’s a really wise thing that nature has done for us – it’s telling us that we are in danger, so we need to listen to that pain.”

So why does our body experience different levels of pain at different times of the day? It might have something to do with circadian rhythms.

“We… identified a circadian rhythm of pain sensitivity,” Inès Daguet, who studies pain perception and assessment at the French Institute of Health and Medical Research, told IFLScience. “In healthy humans… the worst times of day for pain are in the middle of the night (around 4 AM) and the best times are in the middle of the afternoon (around 4 PM).”

Researchers discovered a surprising omission in the connectivity between sleep and pain.

“Many previous studies had shown an impact of sleep on pain sensitivity, so we expected a strong sleep effect. On the [other] hand, the impact of the circadian system was rarely studied in the correct conditions and was therefore commonly underestimated.”

It’s incredibly challenging to factor in circadian rhythms with studies as they rely on highly-controlled laboratory environments and take 24 hours to properly achieve. But as the study points out, it’s a key system in regulating the body in a number of ways.

The circadian timekeeping system plays a key role in physiology by regulating the rhythmicity of numerous functions, from gene expression to cortical activity and behavioral functions.

It is, therefore, also likely to be involved in pain perception.

The surprising lack of knowledge about the rhythmicity of pain sensitivity may result from the impact of timing on pain perception rarely having been taken into account, and the use of inappropriate protocols for the exploration of pain rhythmicity from a neurobiological and mechanistic point of view.

It’s a factor that could date back thousands of years.

“I personally believe that there could be a relationship with the fact that originally, we (as animals) needed to be more sensitive at night when we slept in order to wake up quickly in case of a danger,” Dauget said.

De la Vega had an additional explanation.

“[Throughout] our circadian rhythm, several things happen to our body,” she explained. “One of them is the release of certain hormones at different times of the day – in the morning we have a peak of cortisol… and then at night we release melatonin, and that’s what makes us feel sleepy… That would be my wild guess.”

All that to say, there are certainly still more questions than answers when it comes to how the body receives and regulates pain – and what sleep, and your sleep cycle – have to do with both.

The explanation could be more simple though, as researchers agreed, pain response could simply mean that you’re just tired.

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