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EFFECTS OF SODIUM BICARBONATE ON MARKERS OF KIDNEY INJURY DURING REPEATED SPRINTS IN THE HEAT

Abstract

PURPOSE: To investigate if sodium bicarbonate (SB) supplementation reduces markers of acute kidney injury (AKI) after maximal repeated sprints in the heat. METHODS: Using a randomized, crossover, double-blind design, 10 endurance athletes (4 female) ingested capsules containing 0.2 g/kg of SB or placebo 1 hr before exercise. Participants completed a 22 min cycling warm-up followed by 4 sets of 5x6-sec maximal sprints (24 sec rest between sprints, 5 min rest between sets) on a cycle ergometer in a heat chamber (40 °C, 20% RH). Core temperature (Tc) was recorded at baseline and post-exercise. Urine samples were collected pre-capsule ingestion and pre-, post-, and 1 hr post-exercise to measure urine flow rate (UFR), specific gravity (USG), and pH. Urine samples from pre-ingestion and 1 hr post-exercise were analyzed for the product of insulin-like growth factor-binding protein 7 and tissue inhibitor of metalloproteinase 2 (IGFBP7•TIMP2), a biomarker of AKI risk. Blood was collected pre-ingestion, pre-, and post-exercise to estimate bicarbonate (HCO3). RESULTS: Blood HCO3 was higher in the SB post-ingestion (SB: 26 ± 2 mmol/L, Placebo: 22 ± 2 mmol/L; p = 0.03) but not different pre-ingestion or post-exercise (p > 0.05). There were no differences between conditions for USG or UFR (p > 0.05). Tc increased from pre- to post-exercise (p < 0.01), with no differences in post-Tc between SB (38.1 ± 0.4 °C) and placebo (38.0 ± 0.4 °C) (p = 0.25). SB increased urine pH at pre- (6.9 ± 0.9 vs 6.1 ± 0.2; p < 0.01), post- (7.6 ± 0.8 vs 6.0 ± 0.2; p < 0.01), and 1 hr post-exercise (8.1 ± 1.1 vs 6.0 ± 0.2; p < 0.01) versus placebo, respectively. IGFBP7•TIMP2 increased from pre- to 1 hr post-exercise (p = 0.01), but there was no condition effect (p = 0.06). Although not statistically significant, concentrations at 1 hr post were 2.5x lower on average in the SB (0.30 ± 0.30 ng/mL2/1000 vs 0.74 ± 0.79 ng/mL2/1000), which may have clinical relevance. Additionally, 6 participants in the placebo exceeded the 0.3 ng/mL2/1000 threshold for increased risk of AKI, while only 4 participants passed this threshold in the SB. Notably, a negative correlation was observed between post-exercise blood HCO3 and ΔIGFBP7•TIMP-2 (R = -0.64, p < 0.01). CONCLUSION: SB supplementation before repeated maximal sprints in the heat may attenuate the risk of AKI, but further research is needed.

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