Study design
This study was a randomized, single-blind (study participants), placebo-controlled, crossover clinical trial that was conducted between April 2021 and October 2021 by the Division of Pediatric Cardiology and Intensive Care, University Hospital, LMU Munich (Munich, Germany). The study was registered in the German Clinical Trials Register (Subjects were asked to abstain from caffeine (e.g., personal ED intake, coffee, tea, chocolate) and drugs (e.g., tobacco, alcohol) 48 h before and 24 h after study participation. Prior to each study day, an overnight fast (with allowance of water) was requested. Study participants were asked not to consume any food or liquids within the first 4 h after beverage consumption. The randomization into one of two intervention phases was executed by coin flipping. Study participants were given either a commercially available caffeinated ED or a placebo drink without the typical ED components (e.g., caffeine, taurine) on 2 consecutive days. The administered ED dosage was bodyweight-adjusted (3 mg caffeine per kilogram of bodyweight) and reflected the maximum daily caffeine intake for healthy children and adolescents as proposed by the EFSA.