Author(s): ITO, R., UCHIDA, M., KOJIMA, C., FUJIE, S., IEMITSU, K., SHINOHARA, Y., IEMITSU, M., Institution: RITSUMEIKAN UNIV, Country: JAPAN, Abstract-ID: 1997

INTRODUCTION:
High-intensity or prolonged exercise induces a transient reduction of salivary secretory immunoglobulin A (sIgA), a key oral immune factor, as well as changes in other salivary immune factors. Recent studies suggest that androgens play an important role in immune regulation. Dioscorea esculenta contains diosgenin, a steroidal saponin reported to increase circulating androgen levels. However, its effects on salivary sIgA responses to acute exercise remain unclear. Therefore, this study aimed to examine the effects of Dioscorea esculenta intake on baseline and exercise-induced changes in salivary sIgA, and to explore its relationship with salivary human β-defensin-2 (HBD-2).
METHODS:
Twelve healthy untrained young men completed a randomized, double-blind, placebo-controlled crossover study in which participants ingested Dioscorea esculenta (DIO) or placebo (PLA) for 14-day interventions, with a 7-day washout. Participants performed a 90-min cycling bout at 55% maximal oxygen uptake exercise intensity at four time points: before (W0) and after 14-day supplementation (W2) in both trials. Saliva samples were obtained at baseline, immediately after exercise (post-0 min), and 60 minutes after exercise (post-60 min). Salivary sIgA and HBD-2 concentrations were measured using enzyme-linked immunosorbent assays. Salivary secretion rates were calculated by multiplying sIgA or HBD-2 concentration by flow rate. A three-way repeated-measures ANOVA was used to compare among three factors: time point (baseline, post-0 min, post-60 min), trial (DIO and PLA), and intervention (W0 and W2). Statistical significance was set at p < 0.05.
RESULTS:
In both trials, the salivary sIgA secretion rate significantly decreased from baseline to post-0 min and significantly increased at post-60 min compared to post-0 min (p < 0.05). At each time point, the salivary sIgA secretion rate at DIO-W2 was significantly higher than DIO-W0 at baseline (DIO-W2: 253.0 ± 89.6 μg/min vs DIO-W0: 165.6 ± 73.6 μg/min, p < 0.05) and post-0 min (DIO-W2: 187.6 ± 56.6 μg/min vs DIO-W0: 111.0 ± 39.2 μg/min, p < 0.01). Salivary HBD-2 secretion rate significantly increased from baseline to post-0 min and post-60 min (p < 0.05). The area under the curve for percentage changes from baseline to post-60 min showed a significant negative correlation between salivary sIgA and HBD-2 secretion rates (r = −0.319; p < 0.05).
CONCLUSION:
Dioscorea esculenta intake increased baseline salivary sIgA secretion, allowing higher sIgA levels to be maintained despite acute exercise-induced reductions. In addition, the inverse relationship between salivary sIgA and HBD-2 responses suggests a coordinated oral immune defense during exercise.