Caffeine Linked to Brain Differences in Young People

Caffeine Linked to Brain Differences in Young People. That iced coffee before class, the energy drink at the gym, the soda at lunch: caffeine is so ordinary that most of us never think of it as a drug. But a new study of 9,632 children aged 9 to 11 in the United States suggests even modest amounts can leave traces on a developing brain. Children who consumed caffeine, mostly from soft drinks, slept less and showed small differences in the surface area of the cortex, the brain's folded outer layer that handles attention, decision-making and emotions. The pattern was reported in October 2026 in Biological Psychiatry: Cognitive Neuroscience and Neuroimaging by a team at the Institute of Psychiatry, Psychology & Neuroscience at King's College London, according to reporting by Medical Xpress on the findings.

The scale of caffeine use among young people is easy to underestimate. Studies have found that two-thirds of adolescents take in caffeine at least once a week, and unlike alcohol or tobacco, it faces almost no regulation. "Caffeine is such a normal part of daily life that it's easy to forget young people are consuming it too," said senior author Dr. Divyangana Rakesh, a senior lecturer in neuroscience and psychology at the IoPPN. "Despite it being a psychoactive substance, it is completely unregulated," she added. The children in the study, who were taking part in a long-running U.S. brain development cohort, reported how many caffeinated drinks they usually had each week, whether coffee, tea or soft drinks, while parents reported average sleep duration.

What showed up on the brain scans

MRI scans measured the thickness and surface area of each child's cortex. Higher caffeine intake was associated with slightly lower total cortical surface area, even after the researchers adjusted for household circumstances like parental education and income. The differences were spread across 22 separate brain regions in all four lobes, and they were largely driven by soft drink consumption, the biggest caffeine source in the group. Perhaps most striking: the effect was detectable from as little as one caffeinated drink a week, compared with none at all.

The researchers then traced the chain linking the drink to the brain. Young people who consumed more caffeine slept less, and shorter sleep was in turn linked to lower surface area. Together, reduced sleep and lower surface area partly explained why higher caffeine intake predicted more mental health problems, including difficulties with attention, mood and behavior, when the children were checked again half a year later. At the 18-month follow-up, only the path running through overall surface area was still present.

Why sleep looks like the key link

That middle link matters because it is the part most of us can act on. Rakesh added that even fairly low intake was associated with small structural differences and later mental health, with lower sleep duration looking like an important underlying link. The researchers caution that they cannot say caffeine causes these changes, only that the association is there. For teens who joke that they run on energy drinks and short nights, the finding reframes the trade-off: the drink may not just cost you hours of sleep, but the depth of the sleep you get.

This is not the first time science has caught caffeine changing what the brain does at night. Last year, University of Montreal researchers reported in Communications Biology that caffeine kept the brain in a more active, wake-like state during sleep, and that the disruption was significantly stronger in 20- to 27-year-olds than in adults aged 41 to 58, especially during REM sleep. The younger adults' stronger response was tied to a higher density of adenosine receptors, the targets caffeine blocks. In other words, young brains appear more sensitive to the stimulant's nighttime effects, a result reported by the outlet at the time.

A brain-wave review found the same pattern

More recently, a systematic review from Wroclaw Medical University pulled together 32 brain-wave studies and found caffeine most consistently suppressed slow-wave activity, the electrical signature of deep, restorative sleep. The review, summarized by Medical Daily, found these changes even when total sleep time looked normal and people said they felt fine: the clock reported a full night while the brain recorded a lighter one. Doses as low as 100 milligrams were enough to weaken early-night slow waves in some studies, and in one experiment, drinking caffeine before bed cut early-night deep sleep nearly in half in late-middle-aged adults. The new London study now adds a longer view to that picture: not just a restless night, but a structural signature in the developing cortex.

What the study cannot prove yet

There is an important caveat, and the researchers state it plainly. Soft drinks were the main caffeine vehicle in the study, and soft drinks bring a lot more than caffeine: sugar, and often less healthy lifestyle habits and more risk-taking behaviors. "We can't yet separate the role of caffeine from everything else that comes with them," said first author Jiayi Zheng, noting the next step is to track more precisely what young people drink, when they drink it and how well they sleep. In plain terms, caffeine might be a marker for a lifestyle, not the mechanism itself. Until that is untangled, nobody should read this as proof that one weekly soda rewires a brain.

Still, the authors say both caffeine intake, including from soft drinks, and sleep deserve attention in conversations about youth mental health. For Gen Z, that conversation is practical, not abstract. If you reach for an energy drink to survive a late shift or a study session, consider what the reviews keep concluding: caffeine changes the brain's night even when you feel rested, and shorter, lighter sleep sits at the center of a chain that runs from the drink to mood and attention. Cutting back late in the day and protecting sleep hours is the lowest-stakes experiment a reader can run on themselves. The science on exactly why is still catching up, but it keeps pointing the same direction.