Frequent energy drink consumption among teenagers may be less about the drinks themselves and more a sign that adolescents are not getting enough sleep, according to a new study from the Department of Physical Education and Sport Science (TEFAA) at the University of Thessaly.
The study, titled "Energy Drink Use and Adolescent Sleep Debt: Implications for Obesity, Cognition, and Physical Activity," was published in the scientific journal Nutrients. It examines how frequent energy drink use by teenagers may relate to sleep, physical health, cognitive function and physical activity.
Energy drinks are often marketed as a quick way to boost energy, sharpen focus or improve performance in study or sport. The researchers argue the drinks should not be treated only as a matter of sugar or caffeine intake, but as a possible marker of inadequate sleep and reduced recovery.
Adolescence is a period of intense physical, hormonal and mental development, and sleep at this age is essential for memory, learning, mood, appetite regulation, growth hormone release, physical recovery and motivation to be active. When sleep is reduced or disrupted, teenagers may feel tired, seek out more caffeine, move less, struggle to concentrate and make unhealthier food choices, creating a cycle of less sleep, more need for stimulation, more fatigue, less physical activity and a possible increased risk of weight gain.
What the researcher says drives the cycle
Professor Georgios K. Sakkas of the University of Thessaly's TEFAA department, who led the research, told the Athens-Macedonian News Agency (APE-MPE) that the study's core message is that frequent energy drink use can be a sign a child is not sleeping enough and is trying to function on artificial energy. He said this matters because sleep is linked to concentration, mood, appetite, physical activity and ultimately the risk of weight gain.
Asked whether energy drinks cause obesity, Sakkas said that would be an exaggeration. He said the drinks are not claimed to cause obesity on their own, but can be part of a cycle: a teenager sleeps too little, feels tired, drinks an energy drink, the caffeine delays sleep further, and the next day the teenager feels tired again, reducing motivation for physical activity and sports participation. He said that combined with long hours of screen time, poor diet and little time for physical activity, this pattern can contribute to a heightened risk of obesity.
Sugar versus "zero" energy drinks
Asked whether there is a difference between sugary and "zero" sugar energy drinks, Sakkas said the difference is not so simple. Sugary drinks add calories and are often linked to a broader unhealthy dietary pattern, he said, while sugar-free versions remove that direct calorie load but usually still contain caffeine. He said a "zero" energy drink may not add sugar, but if consumed in the afternoon or evening it can still affect sleep and, the following day, fatigue, mood and concentration.
Effects on thinking and learning
Sakkas said many teenagers drink energy drinks to stay awake, study longer or concentrate better, but this creates a paradox: they may feel temporarily more alert, but if the caffeine disrupts their sleep, the next day they can have worse attention, slower thinking, reduced working memory and weaker self-control. He said this is not permanent cognitive decline but cognitive strain, meaning reduced ability to concentrate, worse decision-making, more impulsiveness and greater difficulty resisting sweets, snacks or sedentary habits.
Asked whether the problem is limited to school performance, Sakkas said no. He said sleep affects school performance but also everyday self-regulation, noting that a tired teenager may struggle to organise study time, get up for training, choose healthier food or control screen use. He said the cognitive effect of poor sleep is not only about studying less effectively, but also about being less able to manage behaviour throughout the day.
Growth hormone and the importance of sleep
On growth hormone, Sakkas said it is released mainly during deep sleep and is important for growth, tissue repair, muscle adaptation and the body's overall anabolic function. He cautioned that it has not been proven that energy drinks directly reduce growth hormone in teenagers, but said that when sleep is consistently short or of poor quality, the body loses part of the time it needs for biological recovery, which can matter for growth, fitness and body composition.
He said adolescence is a period of growth, learning and intense change, and teenagers need adequate sleep to concentrate, remember better, regulate mood and have energy to be active. When sleep is short or irregular, he said, fatigue, cravings for sweets or easy calories, and sedentary behaviour can increase, meaning adolescent obesity is not only a matter of calories but also of sleep, recovery and daily habits.
What parents and pediatricians should ask
Sakkas said it is not enough to ask a teenager whether they drink energy drinks. Parents and doctors should ask when they drink them, how often, in what quantity, for what reason, and whether they are used because the teenager feels tired. He said it is equally important to ask what time the teenager goes to sleep, whether they wake up rested, how much time they spend on screens in the evening, and whether they feel enough energy for physical activity. He said that where obesity, sleep disorders, learning difficulties or attention symptoms are present, the assessment should be even more thorough.
Sakkas concluded that the solution is not simply banning energy drinks. He called for a combination of measures: less caffeine, especially in the afternoon and evening; better sleep habits; limiting screens before bedtime; support for physical activity; and awareness efforts in schools and families. He said the real question is not only what a teenager drinks, but why they feel they need a stimulant to get through the day, and that answering that question is what allows for meaningful help.
