Ad Libitum Drinking Does Not Mitigate Acute Kidney Injury Risk nor Elevations in Oxidative Stress or Inflammation during Simulated Occupational Heat Stress

This study tested the hypothesis that ad libitum fluid intake during a two-hour occupational heat stress simulation attenuates increases in renal oxidative stress, inflammation, and acute kidney injury (AKI) risk compared to fluid restriction. Thirteen healthy adults (5 women) completed two 2-hour occupational heat stress simulations consisting of eight circuits of treadmill walking and rowing exercise in a wet bulb globe temperature of 33.1±0.2°C. In the drinking trial (Drink), participants were provided 237 mL of a non-caloric sport drink every 15 minutes and drank ad libitum. In the fluid restriction trial (NoDrink), no fluid was provided. Urine and blood samples were analyzed for markers of oxidative stress (thioredoxin-1, TRX-1), inflammation (monocyte chemotactic protein-1, MCP-1), and AKI risk ([IGFBP7•TIMP-2]). During Drink, ad libitum fluid intake was 1394 ± 316 mL and reductions in body weight were greater in NoDrink (1.3±0.8% vs. 2.8±0.9%, p<0.001). Peak core temperature was not different between Drink (38.5±0.4°C) and NoDrink (38.6±0.4°C, mean diff. (upper, lower CI): 0.1 (0.4, −0.1)°C; p=0.346). Urine, but not serum TRX-1 (p=0.254), was elevated at post- and recovery (p<0.001) but not different between trials (p=0.743). Serum and urine MCP-1 were elevated at post- and recovery (p<0.001) but not different between trials (p≥0.407). Urine [IGFBP7•TIMP-2] was elevated at post- and recovery (p<0.001) but not different between trials (p≥0.096). Ad libitum fluid intake during a 2-hour occupational heat stress simulation does not modify biomarkers of systemic and renal oxidative stress and inflammation nor AKI risk compared to when fluid is restricted.