Water and the heart: association, not proof

The claim likely comes from a 2002 cohort study of 20,297 Adventist Health Study participants who had no heart disease, stroke, or diabetes at baseline. Over six years, 246 fatal coronary heart disease events occurred; five or more glasses of water a day were associated with lower fatal-CHD risk than two or fewer. This is an observational association, not proof that water prevents a heart attack: the study did not assign water intake and cannot establish causation. Fluid needs vary, so five glasses is not a universal medical prescription. [1–3]