Effect of Sodium Bicarbonate on [HCO3-], pH, and Gastrointestinal Symptoms

Context: Sodium bicarbonate (NaHCO3) is often ingested at a dose of 0.3 g/kg body mass (BM), but ingestion protocols are inconsistent in terms of using solution or capsules, ingestion period, combining NaHCO3 with sodium citrate (Na3C6HSO7), and coingested food and fluid. Purpose: To quantify the effect of ingesting 0.3 g/kg NaHCO3 on blood pH, [HCO3-], and gastrointestinal (GI) symptoms over the subsequent 3 hr using a range of ingestion protocols and, thus, to determine an optimal protocol. Methods: In a crossover design, 13 physically active subjects undertook 8 NaHCO3 experimental ingestion protocols and 1 placebo protocol. Capillary blood was taken every 30 min and analyzed for pH and [HCO3-]. GI symptoms were quantified every 30 min via questionnaire. Statistics used were pairwise comparisons between protocols; differences were interpreted in relation to smallest worthwhile changes for each variable. A likelihood of > 75% was a substantial change. Results: [HCO3-] and pH were substantially greater than in placebo for all other ingestion protocols at almost all time points. When NaHCO3 was coingested with food, the greatest [HCO3-] (30.9 mmol/kg) and pH (7.49) and lowest incidence of GI symptoms were observed. The greatest incidence of GI side effects was observed 90 min after ingestion of 0.3 g/kg NaHCO3 solution. Conclusions: The changes in pH and [HCO3-] for the 8 NaHCO3-ingestion protocols were similar, so an optimal protocol cannot be recommended. However, the results suggest that NaHCO3 coingested with a high-carbohydrate meal should be taken 120-150 min before exercise to induce substantial blood alkalosis and reduce GI symptoms.