Effects of caffeine consumption on intraocular pressure during low-intensity endurance exercise: A placebo-controlled, double-blind, balanced crossover study.

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).