‘Dehydrating’ effects of coffee — we were told wrong!
All this time, we were made to believe that we should avoid coffee because it is a diuretic (stimulates urination) and it will dehydrate us. They were so wrong.
Researchers at the University of Birmingham in the U.K. studied the fluid levels of 50 men who had a habit of consuming about three to six cups of coffee each day.
In order to compare the hydrating effects of coffee and water on these men, each participant had to complete two stages. In the first stage, they drank coffee as their main source of hydration; about 4 mugs of black coffee a day for 3 days. On the second stage, the participants went off coffee and drank equal amounts of water.
The study of the effect of coffee, and caffeine, on fluid balance can be split into two distinct areas: caffeine intake during exercise and caffeine intake at rest in the general population. The research shows that moderate caffeine consumption does not lead to dehydration in the general population. Also concluded is that during exercise, caffeine is beneficial for endurance performance. But does coffee cause dehydration? According to them, no.
The mild, short-term diuretic effect of caffeine is not strong enough to counter-balance the benefits of fluid intake from coffee drinking. After all, black coffee contains more than 95% water.
Killer SC, Blannin AK, Jeukendrup AE (2014) No Evidence of Dehydration with Moderate Daily Coffee Intake: A Counterbalanced Cross-Over Study in a Free-Living Population. PLoS ONE 9(1): e84154. doi:10.1371/journal.pone.0084154