St. Andrews, Scotland – A team of researchers at the University of St. Andrews in Scotland has challenged conventional wisdom regarding hydration, concluding that milk is a more effective fluid for maintaining hydration levels than water. The findings, stemming from a comparative study examining the physiological responses to 13 different beverages, suggest that the composition of liquids plays a crucial role in fluid retention.
The study, led by Professor Ronald Maughan of the Faculty of Medicine at St. Andrews, evaluated variables including fluid intake volume, energy density, electrolyte concentration, and the presence of diuretic agents. Researchers discovered that beverages containing moderate amounts of sugar, fat, or protein demonstrated a superior ability to conserve fluids over extended periods compared to water alone. The results, published in the American Journal of Clinical Nutrition, indicate that the body’s biological response to ingested liquids is key to effective hydration.
The mechanism behind milk’s superior hydrating properties lies in its molecular structure. The presence of lactose, proteins, and fats slows the emptying of the stomach, prolonging hydration. This delayed gastric emptying allows for a more sustained release of fluids into the body, unlike beverages lacking these nutrients. According to the research, the sodium content in milk also contributes to enhanced hydration. Sodium acts like a sponge, retaining water within the body and reducing urine production.
“The sugars, proteins and fats naturally present in milk aren’t just about energy; they influence how our bodies process fluids,” explained researchers in a statement. The study compared both whole and skim milk, finding that both outperformed water in hydration indices.
The research builds on earlier work questioning the primacy of water as the ultimate hydrator. A 2023 study from the same university, as reported by LaSexta, found that while water provides rapid hydration, beverages with added nutrients offer a more prolonged effect. This earlier research also noted that the volume of liquid consumed impacts the speed at which it’s absorbed into the bloodstream, but that nutritional composition ultimately determines how long the body retains those fluids.
The findings have implications for athletes and individuals engaged in strenuous physical activity, where maintaining optimal hydration is critical. The study suggests that incorporating milk into post-exercise recovery routines could be more beneficial than relying solely on water. Although, researchers caution against interpreting the results as a dismissal of water’s importance, emphasizing that all fluids contribute to overall hydration.
As of February 16, 2026, the University of St. Andrews has not issued further statements regarding potential applications of the research or plans for additional studies.