Effects of carbohydrate beverage ingestion on the salivary IgA response to intermittent exercise in the heat

Journal Title (Medline/Pubmed accepted abbreviation): Int J Sports Med
Year: 2011
Volume: 32
Number: 9
Page number: 659-665
doi : 10.1055/s-0031-1271698

Summary of background and research design:

Background: Compared with exercise in thermoneutral conditions, exercise in the heat exacerbates hormonal and immune responses, including reductions in salivary flow and immunoglobulin A (IgA) secretion rates and increased cortisol levels that can inhibit salivary IgA transport. Together, these factors may contribute to higher levels of oral pathogens and an increased risk of upper respiratory infections. Fluid intake, especially if carbohydrates (CHO) are included, may ameliorate these responses, in part, through CHO-mediated attenuation of cortisol response.

Hypothesis/purpose: The purpose of this study was to evaluate the effects of CHO supplementation on salivary IgA and cortisol responses during soccer-specific intermittent exercise in a hot environment.

Subjects: Ten males who regularly participated in physical exercise (3 times/wk) participated in this study (mean age, 26 ± 4 y; height, 1.8 ± 0.05 m; weight, 74.2 ± 5.7 kg; body mass index, 23.4 ± 2 kg/m 2; maximal oxygen consumption [VO2max], 62.6 ± 5.6 mL/kg/min). Salivary responses are based on 8 men.

Experimental design: Randomized, double-blind, cross-over

Treatments Protocol: Participants were randomized to receive an orange-flavored drink containing either 6% (weight/volume) CHO or a sweetener (placebo), with fluid volume based on body mass (3 mL/kg). Participants completed an exercise session with each drink separated by 7 days. Equal portions were drunk at 5 minutes before the exercise and at 15-minute intervals during the 90-minute exercise. Each exercise session consisted of a warm-up (stretching exercises and a 5-min treadmill run) and six 15-minute exercise periods with a 15-minute intermission in the middle at 30° C and 40% relative humidity. Each exercise period represented 5 different exercise categories (standing, walking [4 km/hr], jogging [10 km/hr], cruising [13 km/hr], and sprinting [19 km/hr]). Expired gas volumes were collected every 10 seconds. Heart rate and core body temperature were monitored continuously. Saliva samples for IgA and cortisol levels and calculation of salivary flow rate were collected before exercise and immediately, 24 hours, and 48 hours after exercise. Thermal sensation and rating of perceived exertion (RPE) were recorded every 15 minutes. Gut fullness and thirst levels were recorded before and after drink ingestion before exercise and the intermission period.

Summary of research findings:
  • In general, physiologic changes to the exercise protocol were as expected, with a main effect of time.
  • Heart rate was slightly, yet significantly, higher in the CHO group compared with the placebo group (158 vs 155 beats/min, respectively; P < .05).
    • Thermal sensations, RPE, gut fullness, body mass changes, and core body temperature were not different between the drink groups.
  • Thirst was significantly different between the drink groups (P < .05); which group was higher was not indicated.
  • Salivary flow rate increased throughout the exercise in the placebo group (main effect of time, P < .016).
    • Salivary flow rate decreased throughout the exercise in the CHO group (main effect of time, P = .015; differences between groups, P = .055).
  • Salivary IgA levels did not significantly change between time points or between groups.
    • Post-exercise, salivary IgA secretion rates were numerically higher in the CHO group than in the placebo group.
  • Salivary osmolality and IgA-to-osmolality ratio were not different between groups.
  • Salivary protein secretion was higher in the CHO group than in the placebo group immediately after exercise and 24 hours after exercise (P = .013), although salivary IgA-to-protein ratio was not different.
  • Salivary cortisol levels decreased throughout exercise and 24 hours after exercise in the placebo group and increased immediately after exercise before decreasing at 24 hours in the CHO group.
    • Differences between groups were not significant, but were nearly so.
    • Table 2 in article labels the results oppositely to the text (as above), so it is unclear if it is the text or the table that contains the correct depiction of the data observed.
  • Only solute secretion rate and protein concentration retained significance after comparison for time × treatment.

Interpretation of findings/Key practice applications:

In this study, CHO ingestion did not affect the physiologic responses to exercise in the heat. Higher heart rates in the CHO group may have resulted from an initial and progressive state of dehydration in this group compared with the placebo group.  It is disconcerting that the results reported for salivary cortisol concentrations reported in Table 2 are opposite of those reported in the text.

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