Acute sodium bicarbonate supplementation reduces the increase in markers of acute kidney injury during physical work in the heat

Introduction: In response to metabolic acidosis, compensatory mechanisms are deployed by the kidney to maintain acid–base homeostasis. During physical work in the heat, kidney perfusion is reduced, and the metabolic cost of acid–base balance can make the kidneys more prone to acute kidney injury (AKI). Sodium bicarbonate ingestion (NaHCO₃) may reduce metabolic acidosis and the risk of developing AKI. Purpose: We tested the hypothesis that acute NaHCO₃ supplementation reduces the increase in AKI markers during physical work in the heat. Methods: In a randomized double-blinded placebo-controlled crossover design 8 participants (3 females) completed 2 h of walking at 65% of maximal heart rate in 40 °C and ~ 20% relative humidity (RH) with NaHCO₃ (0.2 g/kg) or a placebo. Urine samples collected pre- and 1 h post-physical work were assayed for insulin-like growth factor binding protein 7 (IGFBP7), tissue inhibitor of metalloproteinase 2 (TIMP-2), and neutrophil gelatinase-associated lipocalin (NGAL). Results: The increase in IGFBP7 × TIMP-2 was lower with NaHCO₃ (Δ log 2.77 ± 1.40 [pg/min]²) compared to placebo (Δ log 4.19 ± 1.77 [pg/min]²) (interaction: p = 0.05). NGAL increased from pre to 1 h post in the placebo (Δ log 2.55 ± 0.99 pg/min) and NaHCO₃ (Δ log 1.94 ± 1.06 pg/min) trials (main effect of time: p < 0.001), but there was no main effect of condition (p = 0.19) or interaction (p = 0.08). Conclusion: These findings suggest that acute NaHCO₃ supplementation may be a beneficial intervention for individuals attempting to mitigate AKI risk during physical work in the heat.