Coffee does not dehydrate you, says new study

A new study published in the journal PLOS ONE says that drinking a moderate amount of coffee does not lead to dehydration. There is a common belief that drinking coffee or other caffeinated drinks can lead to dehydration, and it has long been known that caffeine acts as a mild diuretic. However, the effects of coffee consumption on fluid balance cannot be directly compared to pure caffeine.

Prior to the latest research, only two studies had specifically investigated the effects of caffeine in the form of coffee on hydration. This was the first study to directly assess the effects of moderate consumption of coffee compared to equal volumes of water.

Researchers at the University of Birmingham School of Sport and Exercise Sciences found that drinking moderate amounts of coffee does not lead to dehydration and actually contributes to daily fluid requirements just as other fluids do.

“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,” said Sophie Killer, a doctoral researcher and lead author of the study.

The team measured the effects of moderate consumption of black coffee compared to the consumption of equal volumes of water on fluid balance and hydration status. They tested 50 male participants in two different phases who were already habitually drinking three to six cups of coffee per day.

During the first phase, the participants were asked to drink four mugs of black coffee or water per day for three days. The second phase asked participants to switch, so that those who drank coffee switched to water and visa-versa. Females were not involved in the study because the team wanted to control against possible fluctuations in fluid balance resulting from menstrual cycles.

Researchers used a variety of hydration measures, including body mass, total body water, and blood and urine analyses. They found no significant differences in total body water or any of the blood measures of hydration status between those who drank coffee and those who drank water. They also found no difference in 24-hour urine volume or urine concentration between the groups.

The team wrote that the data from the study suggests that coffee, when consumed in moderation by habituated males, provides similar hydrating qualities to 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,” said Killer. “We conclude that advice provided in the public health domain, regarding coffee and dehydration, should be updated to reflect these findings.”

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