What Does the Beverage Hydration Index Actually Measure? A Construct-Validity Audit

This evidence audit examines what the Beverage Hydration Index (BHI) directly measures and whether a higher BHI supports the broader interpretation that a beverage provides better hydration in a physiologically or functionally meaningful sense. Direct BHI studies indicate that the index is influenced by gastrointestinal absorption kinetics, renal handling, population characteristics, and observation window. A targeted criterion-validity search did not identify a prospective study validating BHI against an independent meaningful endpoint such as cognition, symptoms, clinical outcomes, or exercise performance. Evidence from pre-exercise hyperhydration is treated only as adjacent context and not as a direct validation test of BHI. The report concludes that BHI is best interpreted as a reproducible short-term urine-retention / fluid-balance response to a standardized beverage challenge rather than a universal ranking of hydration quality.