A sleep psychologist points out one of the most common risks of drinking coffee: “It is a double-edged sword”
According to new research, having an afternoon cup of coffee might seem harmless—but caffeine continues to affect the body, especially in young adults, where its impact is more pronounced.
An iced coffee might be the perfect pick-me-up on a hot day, but a new study from the University of Montreal shows that caffeine doesn’t just keep you awake—it also changes how your brain functions while you sleep.
The researchers found that caffeine can reduce not only the amount of sleep, but also its quality and the brain’s ability to recover overnight, a process that is especially critical for young adults. The study revealed that with caffeine still present in the bloodstream, the brain stays in a more “awake” state, making it harder to fall into deep, restorative sleep—the kind needed for rest, productivity, creativity, and even physical performance.
Caffeine increases the complexity of brain signals, making it seem like the brain is still “on.” This heightened alertness keeps the heart rate elevated and the body in a vigilant state rather than in deep sleep—leading to more fatigue upon waking.
Researchers warn that this means the brain may never fully relax, not even while asleep. Over time, this could negatively affect memory and focus.
Julie Carrier, a professor of sleep psychology, explained: “This suggests that even during sleep, the brain remains in a state of activation under the influence of caffeine. While useful for daytime alertness, this condition may disrupt sleep. The brain doesn’t properly relax or recover.”
Young adults are particularly sensitive to this effect because their brains have more adenosine receptors—proteins that normally respond to adenosine, a chemical that signals tiredness. Caffeine blocks these receptors, keeping the brain artificially awake, which can ultimately be harmful to long-term health.
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