The Effects Of Blackcurrant Supplementation On Physiological Responses To Repeated Exercise-Heat Exposures

Purpose: Evaluate the influence of blackcurrant (BC) supplementation on thermoregulation surrounding repeated exercise-heat exposures pre-heat acclimation (HA) and post-HA. We hypothesized that if BC alters thermoregulatory mechanisms, tolerance to exercise-heat stress will be improved. Methods: In a multi-year crossover study, 9 participants(2M,7F; mean±standard deviation [SD]: 24±3 years, 48.8±7.7mL·kg -1 ·min -1 ) completed 5 days of HA (~40°C, ~40% relative humidity, ≥ 60min) without supplementation (CON) and again with 784 mg of BC·day -1 (BC). Two tests of heat tolerance (~40°C, ~40% relative humidity, HTT1: 120 min, 3.1 mph, 2% grade and HTT2: 65% vVO 2 max until rectal temperature reached 39.5°C) were conducted pre-HA and post-HA. Rectal temperature (T rec ) and heart rate (HR) were continuously monitored, and data were extracted at the start and end of each exercise session. Whole-body sweat-loss (WBSL) was calculated. Time to temperature was recorded at HTT2. Data are presented as mean difference (MD) (95% confidence intervals). Dependent samples T-Tests (p<0.05) were used to compare thermoregulatory responses between BC and CON at a single timepoint, whereas a 2x2 repeated measures ANOVA was used to compare thermoregulatory responses between BC and CON pre-HA and post-HA. Results: Regardless of acclimation statues (pre-HA vs. post-HA), values were similar between BC and CON (p>0.05) at each timepoint for end of exercise T rec. , Δ T rec , end of exercise HR, time to temperature, and WBSL at HTT1 and HTT2. For HTT1, there was a main interaction for HA status: lower end of exercise T rec. (CON: 0.31 (0.06-0.56)°C, p=0.018) and HR (CON: 24 (14-33) BPM, p<0.001; BC: 17 (7-26) BPM, p<0.001). For HTT2, there was a main interaction for HA status: lower T rec before exercise (BC: 0.20 (0.08-0.33)°C, p=0.006), greater Δ T rec (BC: -0.16 (-0.26 - -0.06)°C, p=0.005), and lower HR at the end of exercise (BC: 7 (2-13) BPM, p=0.017). There was no significant effect (p>0.05) of supplement status. Conclusion: BC did not substantially alter temperature, cardiovascular, or sweating responses surrounding exercise-heat exposures in the naïve and acclimated states compared to CON. However, following the low intensity long-duration exposures (HTT1) the BC condition resulted in greater improvements in thermal tolerance at HTT2 compared to CON in many individuals, suggesting a possible role in recovery from exertional-heat stress. These variable responses highlight the need for personalized dietary strategies surrounding exercise in the heat for naïve and acclimated individuals to combat exertional-heat stress. DoD BA20029 This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.