A discussion on coffee consumption and dehydration

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A guest post by Dr Sophie Killer

There has been a lot of uncertainty over the role of coffee and other caffeinated beverages in hydration. Due to early research showing the short term effect of pure caffeine as a mild dehydrating agent, there appears to be a common assumption that caffeinated beverages, such as coffee, also have this effect1. However, can the effect of coffee consumption on fluid balance be directly compared with that of pure caffeine? We aimed to investigate this in a study, recently published in PLOS ONE2. Interestingly, prior to publication of our study only two studies had specifically investigated the effects of caffeine in the form of coffee on hydration status3,4, with mixed and inconclusive results.

Our study is the first to directly assess the effects of a moderate consumption of coffee compared to equal volumes of water. In a sample of regular coffee drinkers, we measured the effects of moderate consumption of black coffee compared to the consumption of equal volumes of water on fluid balance and hydration status. 50 male participants were tested in two phases, where they were required to drink four mugs (200ml) of either black coffee or water per day for three days. In the second phase, those who had initially drunk coffee switched to water and vice versa. The two phases were separated by a ten day ‘wash out’ period.

To assess hydration status, we used a variety of well-established hydration measures including body mass and total body water, as well as blood and urine analyses. 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. As such, we conclude that moderate coffee consumption contributes to daily fluid intake and does not lead to dehydration.

Our paper is now available to view online, here.

1 Eddy, N. and Downs, A. (1928) Tolerance and cross-tolerance in the human subject to the diuretic effect of caffeine, theobromine, and thoephylline. J Pharmacol Exper The,r 33:167-174.
2 Killer S.C., Blannin A.K. and Jeukendrup A.E. (2014) No evidence of dehydration with moderate daily coffee intake: a counterbalanced cross-over study in a free-living population, PLOS ONE.
3 Neuhauser-Berthold, B.S., Verwied, S.C. and Luhrmann, P.M. (1997a) Coffee consumption and total body water homeostasis as measured by fluid balance and bioelectrical impedance analysis. Ann Nutr Metab 41:29-36.
4 Grandjean A, Reimers K, Bannick K, Haven M. (2000) The effect of caffeinated, non-caffeinated, caloric and non-caloric beverages on hydration. Journal of the American College of Nutrition, 19(5):591-600.


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