Hydration Status With Caffeinated Beverages Versus Water: Does Habitual Caffeine Intake Matter?

The Beverage Hydration Index (BHI) allows comparison of fluid retention profiles for different beverages relative to water. Whether caffeine with or without electrolytes differentially impairs hydration status after 4 h is unclear. PURPOSE: The effects of commercially-available caffeinated beverages were compared to water on hydration measures to understand whether caffeine habitual intake is an influencing factor. METHODS: Twenty-eight healthy adults participated in a BHI protocol. Beverages were administered in four 250 mL aliquots over 30 min: 500 ml of caffeinated beverage (CAF) with 280 mg, CAF of 280 mg plus electrolytes (CAF + E) or CAF with 100 mg + E and carbohydrates (CAF + CE) along with 500 ml water (1st and 4th aliquot). Urine output was recorded over 4 h. Habitual caffeine intake ranged from 0 to 535 mg/day and groups were stratified by naïve (< 25 mg/day, n = 9) and regular users (> 25 mg/day). Multi-frequency bioelectrical impedance over the post-ingestion period examined change in total body water (TBW). RESULTS: Caffeine dose relative to body mass (BM) was higher for CAF and CAF + E (4.2 ± 0.7 mg/kg BM) compared to CAF + CE (1.6 ± 0.3 mg/kg BM). At 4 h, BHI for CAF (0.86 ± 0.16) and CAF + E (0.91 ± 0.16) was lower (p < 0.001) versus water (1.0 ± 0.0) and CAF + CE (1.01 ± 0.12). Urine mass with CAF and CAF + E was significantly greater (p < 0.01) by 244 g and 162 g versus CAF + CE. After 4 h, net loss in TBW was greater (p = 0.003) with CAF (-1.2 ± 0.6 kg) and CAF + E (-1.1 ± 0.7 kg) compared to CAF + CE (-0.8 ± 0.4 kg). Caffeine habitual intake of participants had no effect on BHI (p = 0.785) across all drinks between naïve (0.94 ± 0.2) and habitual users (0.95 ± 0.12). The % fluid retained after 4 h (based on BM change) for caffeinated beverages was lower (p < 0.001) for CAF (-71.2 ± 21.5%) and CAF + E (-65.1 ± 26.3%) versus CAF + CE (-46.4 ± 18.8%) and did not differ (p = 0.52) based on caffeine habituation. CONCLUSION: A low carbohydrate-electrolyte beverage with moderate levels of caffeine had similar hydration properties compared to water. This differs from beverages where caffeine doses are higher and contain limited levels and/or no electrolytes. Habitual caffeine intake of participants had no apparent influence on diuresis when ingesting a moderate dose of caffeine along with water in a relatively short time frame. Funded by a grant from Liquid IV, El Segundo CA Supported by: Unilever; The Coca-Cola Company