Purpose: The mucosal immune system serves as the first line of defense against pathogens; meanwhile, poor-quality sleep may potentially have detrimental effects on physical recovery and immunity in athletes. The present study aimed to examine the effect of sleep quality and oral immunity on postcompetition infection risk in young swimmers participating in a national swimming event. Methods: Nineteen voluntary adolescent swimmers from a high school were enrolled. Hooper questionnaire, saliva samples, and sleep quality collected on the fifth day before the competition were recorded as baseline data, and saliva and sleep data on the day of the competition, collected before its start, were used as study data. The levels of salivary total protein (TP), a-amylase, salivary immunoglobulin A, lactoferrin, interleukin-6, and cortisol were measured, and athletes` sleep quality was also monitored. Results: Compared with baseline, the Hooper Index indicated a significant decrease in sleep quality and an increase in stress level before the competition. Levels of a-amylase/TP, salivary immunoglobulin A/TP, and lactoferrin/TP significantly decreased on the morning of the competition, whereas interleukin-6 and cortisol levels showed a significant increase. Analysis of sleep variables in relation to postcompetition infections revealed a significant negative correlation between sleep efficiency, total sleep time, and the number of postcompetition medical visits. Conclusions: Our findings suggest that the overall physiological factors contributing to the decline in athletes` salivary levels of a-amylase/TP, salivary immunoglobulin A/TP, and lactoferrin/TP and increased susceptibility to infections after competition may be related to sleep quality on the night before the competition.
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