Effects of combined stress during intense training on cellular immunity, hormones and respiratory infections

Objectives: This study was designed to determine immune and hormonal changes and their relationship with the incidence of upper respiratory tract infections (URTIs) during an extremely stressful military training ( 3 weeks of physical conditioning followed by a 5-day combat course with energy restriction, sleep deprivation and psychological stress). Methods: Blood samples were collected from 21 cadets ( 21 B 2 years old) before training and after the combat course for analysis of leukocyte and lymphocyte subpopulations, serum cytokines [interleukin-6 (IL-6), IL-1 and IL-10], and hormones [catecholamines, cortisol, leptin, total insulin-like growth factor I (IGF-I), prolactin, dehydroepiandrosterone sulfate (DHEAS) and testosterone]. Symptoms of URTI were recorded from health logs and medical examinations during training. Results: After the combat course, total leukocyte and neutrophil counts were significantly increased while total lymphocytes were unchanged. In lymphocyte subsets, NKcells were reduced ( p < 0.01), while CD4+ and CD19+ ( B) cells were increased. Levels of IL-6 were increased ( p < 0.01), while those of IL-1 and IL-10 were unchanged. Norepinephrine and dopamine levels were increased, while those of cortisol were reduced. Levels of leptin, testosterone, prolactin and total IGF-I were reduced, while those of DHEAS were increased. The incidence of URTI increased during the training (chi(2) = 53.48, p < 0.05). After training data analysis showed a significant correlation between URTIs and NK cells ( p = 0.0023). Training-induced changes in immune and hormonal parameters were correlated. Conclusions: Blood NK cell levels are related to increased respiratory infections during physical training in a multistressor environment. The training-induced decreases in immunostimulatory hormone levels may have triggered immunosuppression. Copyright (C) 2005 S. Karger AG, Basel.