Published in the Journal of the International Society of Sports Nutrition, the findings showed that three weeks of supplementation improved the mucosal immunity and hormonal status of participants, along with rates of upper respiratory tract infection (URTI) and mood status after training.
“Maintaining proper immune function and hormone status is important for athletes to avoid upper respiratory tract infection (URTI) and insufficient recovery, which is detrimental to sport performance and health,” the researchers wrote.
They added that deficiency of L-glutamine occurs during periods of high-intensity and prolonged exercise, and that reduced glutamine levels are responsible for the immune suppression associated with increased infection rates observed in overtrained athletes.
Susceptibility to infection
The study noted that combat-sport athletes are particularly susceptible to infection from repeated strenuous bouts of prolonged exercise, given added stressors including the rapid weight loss required to make weight for competition and increased exposure to pathogens shared during close contact.
Previous research links immune suppression to decreased salivary immunoglobulin A (SIgA) and nitric oxide (NO), while changes in the testosterone/cortisol (T/C) ratio are associated with exercise performance.
“Accordingly, athletes’ hormone responses during training and competition could serve as predictors of their recovery status, leading in turn to potential improvement in performance,” the researchers wrote.
The randomized crossover trial recruited 21 high-level combat-sport athletes (13 taekwondo and 8 boxing athletes) from the National Taiwan University of Sport. Participants consumed either a L-glutamine powder (0.3 g/kg body weight) or a maldodextrin placebo in water for three weeks before switching over to the other study group.
Regular training regimens during the study involved two-hour sessions five days a week consisting of warm-up exercises, specific drills and strength and conditioning prior to sparring.
Saliva samples were collected to measure IgA, NO, testosterone and cortisol before and after the study period, while subjective well-being and URTI incidence and duration were measured by wellness assessment and health checklist, respectively.
“To our knowledge, this is the first study reporting that three-week supplementation of L-glutamine after combat training significantly increased the IgA, NO and T/C ratio in saliva, decreased the incidence of URTI and led to better mood status,” the researchers concluded.
These findings, they added, suggest that acute L-glutamine supplementation has the potential to prevent anabolic/catabolic hormonal disturbances caused by prolonged and intensive training to support health and improve sports performance in athletes.
Although the study did not assess inflammatory markers, it suggested that improvement in mood may be due to the anti-inflammatory properties of L-glutamine.
Source: Journal of the International Society of Sports Nutrition
“Supplementation of L-glutamine enhanced mucosal immunity and improved hormonal status of combat-sport athletes”
Authors: Tung-Lin Lu et al.