The eight-glasses-a-day rule never had a study behind it, and what is replacing it is not another number.
Two threads, kept honest:
- A cross-sectional study this summer found Black young adults had higher kidney-stress markers, but the gap mostly vanished once hydration was accounted for. That is an association, not proof that drinking more fixes anything.
- Earlier work from the same group tied underhydration to neighborhood deprivation regardless of race, so the gap may be diet and circumstance, not a choice to drink less.
- The Adapt-Thirst trial, logged on the NIH registry but independently run out of Salzburg and not yet recruiting, is testing why thirst misfires in some people.
There is no correct dose. Anyone selling you one figure is selling the old bottle with a new label.
