Coffee does not cause dehydration, despite popular belief

Drinking coffee does not lead to dehydration, researchers have said, dispelling a common myth about the morning favourite.

Published in PLOS One, researchers at the University of Birmingham School of Sport and Exercise Sciences say there is no link between moderate coffee consumption and dehydration.

On the contrary, they found that coffee contributes to daily fluid requirements just as other fluids do.

Early research that showed caffeine as a mild diuretic has led to a common misconception that caffeinated beverages, lead to dehydration.

However, drinks containing caffeine cannot be directly compared with pure caffeine.

Sophie Killer, lead author of the study, said: "Despite a lack of scientific evidence, it is a common belief that coffee consumption can lead to dehydration and should be avoided, or reduced, in order to maintain a healthy fluid balance.

"Our research aimed to establish if regular coffee consumption, under normal living conditions, is detrimental to the drinker's hydration status."

The team sampled regular coffee drinkers and measured the effect of moderate consumption to drinking equal volumes of water, looking at hydration status and fluid balance.

Fifty male participants were asked to drink four mugs of either black coffee or water for three days. After a 10 day resting period, they were then asked to swap, with coffee drinkers having water and vice versa.

Researchers looked at body mass, total body water and analysed blood and urine samples to assess hydration status. Findings showed no significant differences in total body water between those who drank coffee or water.

"We found that consumption of a moderate intake of coffee, four cups per day, in regular coffee drinking males, caused no significant differences across a wide range of hydration indicators compared to the consumption of equal amounts of water," Killer said.

"We conclude that advice provided in the public health domain, regarding coffee and dehydration, should be updated to reflect these findings."