If you believe you’re impervious to the negative effects of an evening soda or other caffeinated beverage, you might want to listen up. Recent research finds that caffeine can affect sleep in ways beyond cutting your bedtime hours short.
Scientists in Poland reviewed dozens of studies looking at how caffeine might influence the brain’s electrical activity during sleep. They found evidence that caffeine can subtly reduce the time people spend in deep sleep, even if they subjectively report feeling plenty restful in the morning. The findings support the medical advice that we should be mindful about our caffeine intake, especially later on in the day.
“Caffeine reliably alters the neurophysiological architecture of human sleep in a direction consistent with reduced sleep depth and weakened homeostatic recovery,” the researchers wrote in their paper, published in the journal Nutrients.
Caffeine and sleep
Caffeine is the world’s most widely used stimulant, and plenty of people use it to ward off morning grogginess or simply to get a pep in their step. Conversely, doctors generally recommend avoiding caffeine at least six hours before bedtime, since it might affect sleep.
While many people have reported losing a good night’s sleep to caffeine when it’s consumed late in the day, others (myself included) can seemingly drink it whenever without (apparent) harm. To get a better sense of how caffeine can affect sleep, the researchers looked at previous studies examining caffeine use in people who underwent an electroencephalography, or EEG, while sleeping. EEGs are a reliable way to measure how brain activity changes during sleep and can indicate the quality of the rest we’re getting from it.
They reviewed 32 caffeine-related studies, some of which asked people to report how well they slept the night before. And overall, they found a consistent link between caffeine use and reduced slow-wave brain activity, the kind that occurs in non-REM deep sleep, the most restorative stage of sleep. They also found that caffeine was linked to more wakeful patterns of sleep in general. Importantly, these differences could still be found even when people got a healthy amount of total sleep (typically 7 to 9 hours) or when people reported feeling fine.
Subjective experience of sleep quality “did not consistently track objective disturbance—an observation consistent with broader caffeine-sleep literature showing imperfect self-perception of caffeine’s sleep impact,” the researchers wrote.
What to do about caffeine
The researchers note that caffeine’s influence isn’t felt the same by everyone. And any harmful effects it might have on sleep will depend on several factors, including how much you’re consuming, the time of day you’re having it, and your general level of sleep quality to begin with. That might mean that some of us should try to limit our caffeine even outside of evenings.
“It is not only about coffee consumed just before bedtime. For some people, the total amount of caffeine consumed during the day and whether the body has enough time to metabolize it before nightfall may also be important,” said study author Donata Kurpas, a researcher at Wroclaw Medical University, in a statement from the university.
Other research has consistently shown that the benefits of caffeine outweigh its potential harms, so long as you’re consuming it in moderation. But personally speaking, as someone who’s indulged in his fair share of late-night soda runs, this research will definitely make me cut back on that habit.
