IMPORTANCE: Intraocular pressure (IOP) is sensitive to caffeine intake and physical exercise. However, the combined effect of caffeine intake and physical exercise on IOP levels remains unknown. BACKGROUND: We aimed to assess the effects of caffeine consumption before exercise on the IOP behaviour during low-intensity endurance exercise. DESIGN: A placebo-controlled, double-blind, balanced crossover study at the University of Granada. PARTICIPANTS: Eighteen physically active young adults (age = 23.3 ± 2.4 years) participated in this study. METHODS: Participants performed 30 minutes of cycling at 10% of maximal power production after 30 minutes of ingesting a capsule of caffeine (~4 mg/kg) and placebo in two different days and following a double-blind procedure. MAIN OUTCOME MEASURE: IOP was measured at baseline (before caffeine/placebo ingestion), after 5 minutes of warm-up, during cycling (6, 12, 18, 24 and 30 minutes) and recovery (5 and 10 minutes) by rebound tonometry. RESULTS: There was a significant effect of caffeine consumption (P < .001, η = 0.50), showing that the ingestion of caffeine before exercise counteracted the IOP-lowering response to low-intensity endurance exercise. Greater IOP values at 12, 18, 24 and 30 minutes (corrected P-values<.05, ds = 0.90-1.08) of cycling were observed for the caffeine in comparison to the placebo condition. CONCLUSIONS AND RELEVANCE: The ingestion of caffeine (~4 mg/kg) 30 minutes before performing low-intensity endurance exercise counteracts the IOP-lowering effect of low-intensity exercise. These results highlight that the ingestion of a considerable amount of caffeine before exercise should be discouraged for individuals who would benefit from the IOP reduction associated with low-intensity exercise (ie, glaucoma patients or those at risk).
Department of Optics, Faculty of Sciences, University of Granada, Granada, Spain.