Ask Emma: Is coffee dehydrating?


Dear Emma,

I have heard many in the coffee industry refer to coffee as dehydrating, is this true? How much water should I drink to offset my coffee drinking?!


Parched in Portland

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Hi Parched,

This is one of the more common misconceptions of coffee’s effect on the body. Although it is true that caffeine and related compounds do have diuretic (urine forming due to increased blood flow to kidneys) action, us regular coffee drinkers likely do not feel those effects as our bodies develop strong tolerances for such levels. I am happy to report that you are officially in the clear to consume a ‘reasonable’ amount of coffee, and should consider this coffee intake a part of your recommended daily hydration. Recent reviews on this topic noted that ‘normal’ levels of consumption that deliver the amount of caffeine in about two cups of coffee (McCusker and others 2003) will result in little or no diuretic action (Maughan and Griffin 2003; Ganio and others 2007). In fact, most recent studies agree that there is no evidence that normal caffeine consumption in coffee results in loss of hydration (Armstrong and others 2005; Grandjean and others 2000). The exception to this is found in people who ingest a few cups of coffee after being deprived for a period of days or weeks (Maughan and Griffin 2003). These individuals can then experience a short term period where they have to visit the restroom more often than usual. Those of us who regularly consume more than 2-3 cups of coffee per day likely have developed a tolerance for this amount of caffeine and therefore its possible diuretic effect. Remember, brewed coffee is likely more than 97% water, why not enjoy it for all of its benefits, including hydration?


Armstrong LE, Pumerantz AC, Roti MW, Judelson DA, Watson G, Dias JC, Sokmen B, Casa DJ, Maresh CM, Lieberman H & Kellogg M. 2005. Fluid, Electrolyte, and Renal Indices of Hydration During 11 Days of Controlled Caffeine Consumption. International Journal of Sport Nutrition & Exercise Metabolism 15(3):252-265.

Ganio MS, Casa DJ, Armstrong LE & Maresh CM. 2007. Evidence-Based Approach to Lingering Hydration Questions. Clinics in Sports Medicine 26(1):1-16.

Grandjean AC, Reimers KJ, Bannick KE & Haven MC. 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.

Maughan RJ & Griffin J. 2003. Caffeine ingestion and fluid balance: a review. Journal of Human Nutrition & Dietetics 16(6):411-420.

McCusker RR, Goldberger BA & Cone EJ. 2003. TECHNICAL NOTE: Caffeine Content of Specialty Coffees. Journal of Analytical Toxicology 27(7):520-522.