In an intriguing new study by sports hydration experts from Loughborough University, Professor Ron Maughan and his team tracked how long 13 common drinks remain in the human body after being consumed, producing a “beverage hydration index” based on their findings. According to the team, it is known that some fluids last longer in your body than others, providing more long-term hydration. For the trial, published in the American Journal of Clinical Nutrition, they recruited 72 men in their mid-20s and asked them to drink a litre of water each as a baseline marker. The amount of water remaining in the men’s bodies after two hours — ie that they hadn’t excreted through urine — was assigned a score of 1.0. and other drinks were then measured and scored in comparison to the water.

Results showed that four drinks – oral rehydration solutions (the kind used to treat diarrhoea); skimmed milk; whole milk and orange juice – had a significantly higher hydration index than plain water. While the first three had high hydration index scores around 1.5, orange juice also performed slightly better than water with a score of 1.1.

What makes milk so good?

“Normally when you drink, it signals the kidneys to get rid of the extra water by producing more urine,” Professor Maughan said. “However, when beverages contain nutrients and electrolytes like sodium and potassium, as milk does, the stomach empties more slowly with a less dramatic effect on the kidneys.”

Interestingly, caffeinated drinks, including coffee, and sugary beverages had hydration indexes no worse than water, once more dispelling the myth that they promote fluid loss. Although the study was not on athletes and did not relate hydration to exercise, it could prove useful when deciding what to drink after training on a daily basis.

*This article was first published in Athletics Weekly. For more of the latest running and athletics news, plus performance features and much more, grab a copy of the magazine or check out