Decaf coffee may be the last thing on your mind if you’re looking for an afternoon caffeine hit to get you through to the end of the working day.
But if you want to wake up feeling well rested, experts say you should reconsider.
New research has found that drinking just two cups of coffee after midday could be enough to shift the brain towards a more excitable and dynamic state during the night, wreaking havoc on your energy levels.
Canadian researchers said that caffeine––one of the most widely consumed stimulants in the world––can change the structure and complexity of brain activity during different stages of sleep.
Lead author of the study Professor Philipp Thölke said: ‘The widespread use of caffeine among the public makes this topic an important health consideration.
‘Understanding how caffeine affects sleep architecture and brain dynamics can help clarify its impact on neural health,’ he added.
The researchers, from the University of Montreal, analysed the sleep health of 40 healthy adults with moderate caffeine consumption aged 20 to 58-years-old.
Participants spent two nights at a sleep clinic one after ingesting 200mg of caffeine––approximately two cups of coffee––and another after having a placebo.
The researchers found that when people consumed caffeine after midday their sleep quality was signifcantly worse, associated with higher levels of electrical activity in the brain
The researchers used a double-blind design so that they also did not know whether participants were coming into the clinic caffeinated or caffeine-free.
The participants’ sleep quality was monitored using an electroencephalogram (EEG) which records brain activity by picking up electrical signals produced by the brain.
Using a sleep EEG researchers focused on several markers of brain complexity looking at how random a brain signal is, how easily the signal can be compressed and how consistent a signal is over time.
They also looked at the distribution of electrical activity across different frequencies.
The results showed that caffeine mostly affected brain activity during non-REM sleep––the stage of the cycle which is considered the quiet or restful stage.
This stage is split into three distinct phases: a person falls asleep, and then moves from a light sleep into a deep sleep.
At this point a person’s breathing, brain activity and heart rate typically slow down, body temperature drops and eye movement stops.
This is a very restorative phase helping the body repair tissue and muscle and strengthen the immune system.
Caffeine had a big impact on non-REM sleep which is typically associated with repair and restoration
However, researchers found that consuming caffeine after midday had a negative impact on this crucial stage, resulting in less restorative sleep.
‘Caffeine delays but does not prevent sleep, so even though we can sleep under the influence of caffeine, the brain, and therefore also sleep, is impacted by the drug,’ Prof Thölke told PsyPost.
‘It leads to shallower sleep with increased information processing during the sleep stages where the brain normally enters deep restorative rest.’
The researchers also noted certain brain signals were flatter, suggesting that the under the influence of caffeine the brain more closely resembled a ‘critical state’––where the brain is most responsive and adaptable.
They also analysed how age affected caffeine’s impact on the brain and sleep health.
Generally, younger adults aged 20 to 27-years-old were more susceptible to caffeine’s stimulant effects during rapid-eye-movement (REM) sleep compared to middle-aged adults.
Researchers theorised that this could be because older people have less adenosine receptors in the brain.
Adenosine is a chemical that builds up in the brain during waking hours eventually making us feel tired.
Caffeine works by blocking adenosine receptors, making us feel more awake.
The researchers suggested that because older adults have fewer receptors, the blocking effect of caffeine may not be so effective especially in REM sleep.
During non-REM sleep however the effects of caffeine were broadly the same across all age groups.
Researchers concluded therefore that caffeine has the ability to restructure the brain and impact how well we sleep.
However, they acknowledged that their study only included healthy individuals so concluded that the findings could not be extrapolated to individuals with neurological or psychiatric conditions like restless leg syndrome or Parkinson’s.
It comes as a study by The Sleep Charity last year found nine in ten people experience some sort of sleep problem.
Poor sleep has been linked to a number of health problems, including cancer, stroke and infertility.
Experts have long advised that waking up during the night does not necessarily mean you have insomnia, which figures suggest affects up to 14million people in the UK.
Yet, sleep deprivation takes its own toll, from irritability and reduced focus in the short term, to an increased risk of obesity, heart disease and diabetes.
