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  • Writer's pictureChristie Robson

Does caffeine actually dehydrate you?

You’ve probably heard the saying before that coffee dehydrates you. But in fact, drinking moderate* amounts of coffee, and around exercise, doesn’t actually dehydrate you.


If this has just put a smile on your face, keep on reading before you go and grab another coffee…



Many studies over the recent years have looked at different beverages and their effect on hydration status. Drinks included: water, sparkling water, orange juice, beer, milk, oral rehydration solutions (ORS) and coffee. They found that ORS, milk and orange juice were top performers when it came to hydration and retaining fluid, with similar results to drinking plain water. And interestingly, coffee didn’t result in a significantly lower urine output or dehydration.


That’s a similar finding to a study published in the Journal of the American College of Nutrition (Grandjean et al., 2000) which looked at the effects of moderate coffee consumption on hydration levels in healthy adult men and women. The study found that moderate coffee consumption (up to 3 cups per day) did not lead to dehydration and had no negative effects on hydration levels.


Moderate coffee intake: ~3-4 cups per day. This will depend if you’re having espresso, instant, coffee pods, coffee bags or iced coffee drinks. Typical espresso shots contain 80-100mg per shot. So a double shot latte, long black or 8-10oz coffee could be giving you over 200mg of caffeine.
Recommended caffeine daily intakes = 400mg/ day for adults and 200 mg for pregnant women

Another study published in the European Journal of Clinical Nutrition (Armstrong et al., 2005) looked at the effects of moderate coffee consumption on hydration levels in endurance athletes. The study found that moderate coffee consumption before and during exercise did not lead to dehydration and had no negative effects on performance. (Woohoo!) Another interesting aspect is that these effects are in regards to coffee itself, not caffeine. So it’s thought that compounds in coffee may contribute to it’s hydrating benefits.




However, before you go and install coffee on tap, it’s important to keep in mind that just like everything, too much of a good thing can be a bad thing. Studies have found that excessive intakes of caffeine (or coffee) over 500mg/day can lead to dehydration (being a diuretic), along with other health consequences. That’s about 5 espresso shots. But, this threshold will vary depending how sensitive you are to caffeine, and if you’re a habitual drinker. It’s thought that habitual coffee drinkers are less sensitive to caffeine and therefore don’t dehydrate as much.


So, having coffee before you head out for a session can actually be beneficial for you - providing some hydration and also enhancing focus, reducing perceived exertion, and possibly enhancing fat oxidation. We'll explore more of this another time; but for now, you can make your coffee and have it too! Just stay in moderation and don't drink it too late to help your sleep!



Happy eating and training,

Christie



References:
  1. Grandjean, A. C., Reimers, K. J., Bannister, P. A., & Haven, M. A. (2000). The effect of caffeine on fluid balance in man. Journal of the American College of Nutrition, 19(1), 91-94.

  2. Armstrong, L. E., Pumerantz, A. C., Roti, M. W., Judelson, D. A., Watson, G., Dias, J. C., ... & Maresh, C. M. (2005). Fluid, electrolyte, and renal indices of hydration during 11 days of controlled caffeine consumption. European Journal of Clinical Nutrition, 59(9), 976-982.

  3. https://www.trainingpeaks.com/blog/how-well-do-different-drinks-really-hydrate-you/

  4. Killer SC, Blannin AK, Jeukendrup AE. No evidence of dehydration with moderate daily coffee intake: a counterbalanced cross-over study in a free-living population. PLoS One. 2014 Jan 9;9(1):e84154. doi: 10.1371/journal.pone.0084154. PMID: 24416202; PMCID: PMC3886980.



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