A cup of coffee could be a better pain-reliever than drugs, say scientists.
Caffeine, the active ingredient in coffee, was more effective than painkillers like ibuprofen and even morphine.
But it was only effective on pain combined with sleep deprivation.
It means patients’ suffering could be eased with shots of caffeine. It boosts dopamine, the brain’s pleasure-chemical that makes people feel good.
In experiments groups of six to 12 lab rodents were kept awake for as long as 12 hours for one group and six hours for five consecutive days for another.
Then they were exposed to extreme heat, cold, pressure or capsaicin, the chemical in hot chilli peppers.
By measuring how long it took the animal to move away or lick away the discomfort caused by capsaicin, the researchers showed caffeine blocked sensitivity to the pain.
Dopamine boosting drug modafinil also had the same effect. But in mice not deprived of sleep the compounds had no pain-relieving properties.
Sleep physiologist Dr Chloe Alexandre, of Beth Israel Deaconess Medical Centre in Boston, said: “We found that five consecutive days of moderate sleep deprivation can significantly exacerbate pain sensitivity over time in otherwise healthy mice.
“The response was specific to pain, and was not due to a state of general hyper-excitability to any stimuli.”
Surprisingly, common analgesics like ibuprofen did not block increased pain sensitivity caused by sleep loss. Even morphine lost most of its effect.
Dr Alexandre said this suggests patients using these drugs for pain relief might have to increase their dose, increasing their risk for side effects.
Caffeine and modafinil are both drugs used to promote wakefulness, she said.
Rather than just taking painkillers, patients with chronic pain might benefit from sleeping pills coupled with regular daytime doses of caffeine.
Some painkillers already include caffeine as an ingredient although its mechanism of action isn’t yet known.
Both caffeine and modafinil boost dopamine circuits in the brain, so that may provide a clue.
Dr Kiran Maski, a specialist in sleep disorders at Boston Children’s Hospital, said: “Many patients with chronic pain suffer from poor sleep and daytime fatigue, and some pain medications themselves can contribute to these co-morbidities,”
“This study suggests a novel approach to pain management that would be relatively easy to implement in clinical care.
“Clinical research is needed to understand what sleep duration is required and to test the efficacy of wake-promoting medications in chronic pain patients.”
The study published in Nature Medicine used tiny headsets that took ERG (electroencephalography) and EMG (electromyography) readings for each mouse.
Pain physiologist Dr Alban Latremoliere, of Boston Children’s Hospital, said: “For each mouse, we have exact baseline data on how much they sleep and what their sensory sensitivity is.”
Then they deprived them of sleep with entertainment, mimicking what happens with people.
Dr Thomas Scammell, of Beth Israel Deaconess Medical Centre, said: “We developed a protocol to chronically sleep-deprive mice in a non-stressful manner, by providing them with toys and activities at the time they were supposed to go to sleep, thereby extending the wake period.
“This is similar to what most of us do when we stay awake a little bit too much watching late-night TV each weekday.”
To keep the mice awake, researchers kept vigil, providing the mice with custom-made toys as interest flagged while being careful not to overstimulate them.
Dr Latremoliere said: “Mice love nesting, so when they started to get sleepy (as seen by their EEG/EMG pattern) we would give them nesting materials like a wipe or cotton ball.
“Rodents also like chewing, so we introduced a lot of activities based around chewing, for example, having to chew through something to get to a cotton ball.”
Previous research has shown just two cups of coffee almost halved muscle pain after a gym work-out.
