Prolonged physical activity in hot environments imparts cardiovascular strain that diverts blood flow from the splanchnic region and compromises gastrointestinal barrier function. This impairment enables gram-negative bacteria to migrate from the gut into the systemic circulation, increasing plasma lipopolysaccharide (LPS) concentrations and initiating NF-κB–driven pro-inflammatory cascades that heighten the risk of exertional heat illness. PURPOSE: This study synthesized findings from three controlled trials examining the effects of dietary supplementation with berberine, curcumin, and New Zealand blackcurrant on systems-level physiology, perceptual ratings, gut barrier integrity, and inflammatory responses during exertional heat stress. In a series of studies, we tested the hypothesis that these dietary supplements offer protection during exertional heat stress. METHODS: Participants completed a 60-min treadmill run at 60–70% VO 2 max in a hot environment (34–37°C, 25–40% RH) after the following supplementation protocols: (1) berberine (1.5 g/day for 7 days; n=8), (2) curcumin (500mg/day for 3 days; n=8), and (3) blackcurrant extract (600 mg/day for 7 days; n=12). Body temperatures, cardiometabolic data, and perceptual ratings were recorded during exercise. Body fluids (blood and urine) were assessed to determine changes in gastrointestinal (GI) barrier function (I-FABP, lactulose/rhamnose ratio) and inflammatory markers (NF-κB pathway components, cytokines, eHSP70). Data, presented as mean ± SE, were analyzed using two-way repeated-measures ANOVA. RESULTS: Berberine: Lower mean body temperature (37.69±0.08°C vs. 37.84±0.06°C; p=0.030), HR (163±3 vs. 166±3 bpm; p=0.025), RER (0.83±0.01 vs. 0.84±0.01; p=0.050), and respiratory rate (38.8±1.1 vs. 41.4±1.0 bpm; p=0.045) compared to placebo. Perceptual responses were improved (thermal sensation: 9.5±0.4 vs. 12.3±0.5 a.u.; p=0.002; perceived exertion: 11.4±0.3 vs. 13.1±0.4 a.u.; p0.050) were identified. Curcumin: Lower core temperature (38.87±0.20°C vs 39.05±0.19°C; p=0.019), mean body temperature (38.52±0.18°C vs 38.70±0.17°C; p=0.049), HR (182±5 bpm vs. 190±5 bpm; p=0.012), and physiological strain index (8.73±0.76 vs. 9.76±0.57 a.u.; p=0.047) compared to Placebo. The increase in I-FABP was also lower at Post (Curcumin 58% vs. Placebo 87%; p=0.002) and 1h-Post (Curcumin 18% vs. Placebo 33%; p=0.046), and IL-1RA at 1h-Post (Curcumin 77% vs. Placebo 153%; p=0.004). TNF-α increased (p=0.010) from Pre to Post (19%) and 1h-Post (24%) in Placebo but not in Curcumin (p>0.05). IL-10 increased (p0.050). Blackcurrant: Improved rectal temperature (Blackcurrant 39.36±0.46°C vs. Placebo 39.47±0.43°C, p=0.003) and GI barrier integrity (lactulose/rhamnose ratio ↓12%; p=0.003; I-FABP AUC ↓40%; p0.050). There were also no significant differences in HR (Blackcurrant 185±9 bpm vs. Placebo 184±9 bpm, p=0.868) or physiological strain index (Blackcurrant 9.6±0.6 vs. Placebo 9.8±0.7, p=0.799). CONCLUSION: Short-term supplementation with berberine, curcumin, and blackcurrant extract confers distinct benefits during exertional heat stress: berberine improves thermoregulatory and perceptual responses; curcumin reduces physiological strain and GI injury while attenuating pro-inflammatory signaling; blackcurrant enhances gut barrier function without systemic cytokine changes. These findings highlight targeted nutritional strategies to mitigate physiological and gastrointestinal dysfunction during exercise-heat stress. This abstract was presented at the American Physiology Summit 2026 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.
Kuennen et al. (Fri,) studied this question.