Effects of Energy Deficit on Secretory IgA During a Simulated Multi-Stressor Military Operation

Abstract Objectives Secretory IgA (SIgA) is a critical component of mucosal immunity and a first line of defense against pathogens. Intense physical exercise, lack of sleep, and inadequate energy intake are frequently observed during military training and operations. These factors are associated with a decline in SIgA and may increase the risk of infection; however, to what degree each of these factors contributes to immune dysfunction is unclear. This study aimed to determine the effect of severe energy deficit on mucosal immunity (SIgA) during a multi-day period of intense training. Methods The parent study was a randomized, crossover trial in healthy males (n = 10, 22.4 ± 5.4 y, 87.3 ± 10.9 kg) to assess the effect of severe negative energy balance on inflammation, iron absorption, and other physiological and cognitive outcomes during a simulated sustained military operation (SUSOPS; high energy expenditure with repeated bouts of intense exercise). Participants completed two SUSOPS trials and were randomized to consume ± 10% of estimated total daily energy expenditure (TDEE, energy balance) or 45% of TDEE (energy deficit). At 0500 on each SUSOPS day (D1: baseline, D2:24 h, D3:48 h), participants placed polyester oral swabs under their tongue for 3-mins. A second swab was collected (i.e., placed under the tongue until saturation) to ensure adequate sample volume. SIgA secretion rate (μg/min) was calculated from SIgA concentration (μg/mL; enzyme-linked immunosorbent assay) and salivary flow rate (mL/min). Dependent variables were log10 transformed due to non-normal distribution and data were analyzed using linear mixed models. Results Independent of treatment, a main effect of time (P = 0.01) was observed where SIgA secretion rate declined by 20% from D2 [1.77 ± 0.34 μg/min] to D3 [1.41 ± 0.51 μg/min], P = 0.001, with no significant treatment by time interactions. A main effect of time (P = 0.01) was also found wherein SIgA concentration declined by 13% from D2 [2.67 ± 0.32 μg/mL] to D3 [2.33 ± 0.37 μg/mL], P = 0.001. There were no main or treatment effects with regard to SIgA flow rate. Conclusions Mucosal immune response, as measured by SIgA, declined in response to SUSOPS. Severe energy deficit did not exacerbate the decline in SIgA secretion rate observed in response to the high intensity, multi-stressor training scenario. Funding Sources US Army Medical Research and Development Command.