Caffeine Decreases Systemic Urea in Elite Soccer Players during Intermittent Exercise


Medicine & Science in Sports & Exercise: April 2013 - Volume 45 - Issue 4 - p 683–690
doi: 10.1249/MSS.0b013e3182797637
Basic Sciences

Purpose: We investigated the effects of caffeine on the ammonia and amino acid metabolism of elite soccer players.

Methods: In this double-blind randomized study, athletes (n = 19) received 5 mg·kg−1 caffeine or lactose (LEx, control) and performed 45 min of intermittent exercise followed by an intermittent recovery test (Yo-Yo IR2) until exhaustion. The caffeine-supplemented athletes were divided into two groups (CEx and SCEx) depending on their serum caffeine levels (<900% and >10,000%, respectively). Data were analyzed by ANOVA and Tukey post hoc test (P < 0.05 was considered to be statistically significant).

Results: Caffeine supplementation did not significantly affect the performance (LEx = 12.3 ± 0.3 km·h−1, 1449 ± 378 m; CEx = 12.2 ± 0.5 km·h−1, 1540 ± 630 m; SCEx = 12.3 ± 0.5 km·h−1, 1367 ± 330 m). Exercise changed the blood concentrations of several amino acids and increased the serum concentrations of ammonia, glucose, lactate, and insulin. The LEx group showed an exercise-induced increase in valine (∼29%), which was inhibited by caffeine. Higher serum caffeine levels abolished the exercise-induced increase (∼24%–27%) in glutamine but did not affect the exercise-induced increase in alanine (∼110%–160%) and glutamate (42%–61%). In response to exercise, the SCEx subjects did not exhibit an increase in uremia and showed a significantly lower increase in their serum arginine (15%), citrulline (16%), and ornithine (ND) concentrations.

Conclusions: Our data suggest that caffeine might decrease systemic urea by decreasing the glutamine serum concentration, which decreases the transportation of ammonia to the liver and thus urea synthesis.

1Laboratory of Biochemistry of Proteins – Federal University of State of Rio de Janeiro, Rio de Janeiro, BRAZIL; 2Institute of Genetics and Biochemistry – Federal University of Uberlândia, Uberlândia, BRAZIL; 3Biological Sciences and Health Institute – Federal University of Mato Grosso, Mato Grosso, BRAZIL; 4Institute of Neurology Deolindo Couto – Federal University of Rio de Janeiro, Rio de Janeiro, BRAZIL, 5Botafogo de Futebol e Regatas – Rio de Janeiro, BRAZIL; 6National Institute of Traumatic Orthopedics – Rio de Janeiro, BRAZIL; 7Jockey Clube Brasileiro – Rio de Janeiro, BRAZIL; and 8Department of Psychology – University of Virginia, Charlottesville, VA

Address for correspondence: Luiz-Claudio Cameron, Ph.D., Av. Pasteur, 296 – Urca – Rio de Janeiro, Rio de Janeiro, CEP 22290-240, Brazil; E-mail:

Submitted for publication January 2012.

Accepted for publication October 2012.

©2013The American College of Sports Medicine