For caffeine fiends or anyone prone to an afternoon slump, how late in the day to drink coffee has long been an open question.
Depending on how early a person wakes or has their first cup, suggestions range from nothing after noon to something like a 3 pm cut-off.
Drinking coffee any later, the thinking goes, could mean tossing and turning and staring at the ceiling no matter how tired you are.
But according to scientists at Wroclaw Medical University in Poland, the “controversy” has been looked at the wrong way: The issue is not whether or not coffee delays sleep, it is what happens to the nocturnal brain on caffeine.
The effects do not always manifest as shorter sleep or difficulty falling asleep, the team found, warning that the damage is done to quality of nighttime rest by causing "shallow" sleep.
"The body may spend eight hours in bed, but the brain may fail to fully regenerate," the researchers said, citing information gleaned from electroencephalography, or EEG brain screening.
"People are often unaware of this," the university explained in a press release, pointing out that coffee affects people differently depending on an array of factors including age, metabolism, fitness and stress.
"EEG allows us to see not only whether a person is sleeping, but also how the brain is sleeping," said Donata Kurpas, professor of nursing at Wroclaw.
So what does this mean for your coffee consumption? The findings suggest that anyone looking to improve their sleep should make sure to give their body enough time during the day to fully metabolize the total caffeine intake before nightfall.
"Caffeine is neither ‘good’ nor ‘bad’," Kurpas says. "It is a biologically active substance whose effects depend on dose, time of day, age, lifestyle, sleep quality, stress burden and individual sensitivity." For some people a morning coffee can be just as risky as a coffee before bedtime for others.
"Quantitative EEG analysis reveals more subtle changes, such as reduced slow-wave activity, which is an important marker of sleep depth and its restorative character," she pointed out, warning that the effects can go unnoticed by people who wrongly believe that they have had a good night's rest.
