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Abstract

Many workers worldwide are exposed to prolonged and hazardous heat stress, physical activity, or a combination of both. Adverse environmental conditions can worsen the physical impacts of occupations such as mining, farm work, construction, and wildland firefighting, making these laborers susceptible to acute kidney injury (AKI). Although underexplored in reducing AKI from work and heat stress, sodium bicarbonate (SB) has been shown to increase plasma volume and decrease oxidative and inflammatory markers, suggesting the potential for reducing the incidence of AKI during work in the heat.PURPOSE: To investigate the efficacy of SB supplementation on mitigating AKI during physical work in the heat. METHODS: Fourteen healthy adults were randomized into SB or placebo (PLA) groups using a double-blind crossover design. Participants completed two experimental trials, rotating through five workstations for two hours. Subjects were encouraged to maintain a moderate intensity effort (11-13 RPE). All work was completed outdoors in the Sonoran Desert during June, with an average wet bulb globe temperature of 94.6°F (34.8°C). Urine kidney stress markers were analyzed using ELISAs. RESULTS: SB significantly increased blood bicarbonate (mean difference: 4.5 ± 0.7 mmol/L, p < 0.001) and base excess (mean difference: 4.5 ± 0.6 meq/L, p < 0.001). Core temperature increased slightly with SB compared to PLA (mean increase of 0.2 ± 0.1°C; 95%CI 0.2- 0.4°C; p < 0.05), with both SB and PLA remaining steady throughout (p=1.0). No difference in hydration status (USG) or fluid intake between conditions (p = 0.72). No significant differences between SB and PLA for kidney stress markers; IGFBP-RP1 (condition p = 0.51; time p = 0.74; interaction p = 0.87), TIMP-2 (condition p = 0.13; time p = 0.11; interaction p = 0.81), and NGAL (condition p = 0.64; time p = 0.88; interaction p = 0.54). CONCLUSION: While SB improved buffering capacity, there was no influence on markers of kidney injury across the two-hour work session in the heat. This study integrated mitigation strategies, including ensuring hydration and following NIOSH work-to-rest guidelines for working in the heat, which could have contributed to the lack of changes in markers of kidney injury. Future research should explore the relationship between duration and intensity.

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