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Does Coffee Dehydrate Us?

Updated: Nov 20, 2023

We all love a cup o’ Joe. But is this popular beverage causing us to be dehydrated? In this article, we get to the bottom of this common claim.


Introduction

We have all been told to not drink too much coffee as it will dehydrate us. But is this truly the case? I mean, there is a plausible rationale that might explain this—and we will touch upon in this article—but as is often the case with the human body, such plausible physiological mechanisms can fail to pan out in reality. Luckily, I have investigated this claim thoroughly. So sit back, relax, and read on to learn what the best available science says.


The relationship between coffee and health.

Coffee consumption is associated with a range of health benefits and little risks. Learn more by reading our earlier article on coffee and health.


Why Coffee Might Dehydrate

The reason we’re told that drinking coffee is dehydrating is because caffeine—one of the main substances in coffee—is a diuretic. What this means is that caffeine makes us pee, and if we pee more, we lose more water from our body. In fact, urine is more than 90% water, so it doesn’t take a genius to figure out that peeing more often could dehydrate us. Further, caffeine may prevent sodium reabsorption in the kidneys, which could lead to more water ending up in our urine (1).


However, we must keep in mind that coffee grounds are just 1–2% caffeine; so the vast majority of a brewed coffee is water (2). So maybe the increased production of urine is offset by the water we drink from the coffee. However, maybe taking caffeine in other forms (e.g., pills or gums) would cause us to be dehydrated as in this case it's not consumed in liquid form. To get to the bottom of this, we need to investigate studies that instructed people to drink coffee or consume caffeine and then monitored urine production or hydration status. Thankfully, such studies exist.


Different types of coffee.

Research on Coffee or Caffeine and Hydration

In a study where 50 men were either given 4 cups of coffee per day (200 millilitres (mL) each) for 3 days, or 4 cups of an equal amount of water per day for 3 days, there were no differences in total body water content from the beginning to the end of either trial, or between trials (3). In a larger analysis of 28 investigations (including 379 individuals) where caffeine was consumed as the intervention, the combined result showed that while caffeine did produce a small increase in urine (+109 mL, or +16%) compared to non-caffeine consumption, the results were not consistent across trials, and whether this would be enough of an effect to cause dehydration is unlikely (1). In fact, when the authors dug a little deeper, they noticed that this effect seemed to disappear when caffeine was consumed during exercise (1). In addition, the doses of caffeine in these studies were quite large (the median dose was 300 milligrams (mg), which is the amount provided by ~4 cups of coffee), so the small increase in urine must be interpreted within this context.


A more recent study showed no real difference between the urine produced after drinking coffee with a caffeine content equivalent to ~3 cups of coffee compared to an equal quantity of water (4). However, when these participants drank coffee with a caffeine content equivalent to ~6 cups of coffee, they produced nearly twice the volume of urine compared to an equal quantity of water (4). Keep in mind that these drinks were consumed in one sitting, so these results may not translate to the real-world, where no one is drinking 6 cups of coffee in one go.


Caffeine and exercise and sports performance.

If you want to know all about how caffeine improves exercise performance, including how much to take, we have covered that before as well.


Summary

All in all, it seems that coffee (or caffeine) is unlikely to cause dehydration. The brand new international society of sports nutrition position stand on coffee and sports performance agrees with this conclusion, stating that ‘...caffeine ingestion prior to exercise does not lead to dehydration’ and that any small increase in urine production when caffeine is consumed at rest is ‘minor’ (2). Further, the 2021 international society of sports nutrition position stand on caffeine and sports performance stated that ‘...the majority of research has confirmed that caffeine consumption does not significantly impair hydration status [or] exacerbate dehydration…’ (5).


To put a bow on it all, here are my three key takeaways:

  1. The consumption of small to moderate amounts of caffeine—through coffee or otherwise—is unlikely to dehydrate you at rest

  2. The consumption of moderate- to high-amounts of caffeine immediately before and during exercise does not seem to cause dehydration

  3. The consumption of high amounts of caffeine at rest—through coffee or otherwise—may increase urine production slightly, but this is unlikely to cause dehydration


If you’re interested in becoming a better footballer, or if your child is, why not book in to our supplemental football coaching services by reaching out to our team of expert coaches at [email protected].


Thanks for reading and, as always, we hope you have a lovely weekend!


Patrick Elliott, BSc, MPH

Health and Nutrition Science Communication Officer at Training121


Health Disclaimer: this article is for informational and educational purposes only, and is not a substitute for professional advice. For health advice, speak to a physician or other qualified health-care professional, and for nutrition advice, speak to a qualified nutrition professional (e.g., registered dietitian). The use of information on this site is solely at your own risk.


References

(1) Zhang Y, Coca A, Casa DJ, Antonio J, Green JM, Bishop PA. Caffeine and diuresis during rest and exercise: A meta-analysis. J Sci Med Sport. 2015;18(5):569–74. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4725310/


(2) Lowery LM, Anderson DE, Scanlon KF, et al. International society of sports nutrition position stand: coffee and sports performance. J Int Soc Sports Nutr. 2023;20(1):2237952. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10375938/


(3) 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;9(1):e84154. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3886980/


(4) Seal AD, Bardis CN, Gavrieli A, Grigorakis P, Adams JD, Arnaoutis G, Yannakoulia M, Kavouras SA. Coffee with High but Not Low Caffeine Content Augments Fluid and Electrolyte Excretion at Rest. Front Nutr. 2017;4:40. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5563313/


(5) Guest NS, VanDusseldorp TA, Nelson MT, Grgic J, Schoenfeld BJ, Jenkins NDM, Arent SM, Antonio J, Stout JR, Trexler ET, Smith-Ryan AE, Goldstein ER, Kalman DS, Campbell BI. International society of sports nutrition position stand: caffeine and exercise performance. J Int Soc Sports Nutr. 2021;18(1):1. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7777221/


Technical Terms

Caffeine: A substance found in coffee that is a central nervous system stimulant, meaning that it improves attention and cognitive performance, and also improves a range of exercise performance outcomes.


Hydration: The process of replacing the lost fluid, particularly water, in something.


Diuretic: Any substance that promotes the increased production of urine (diuresis).


Median: The median value of something is the value bang smack in the middle of all other values, which divides the numbers so that an equal amount are below, and an equal amount are above. In other words, it is the middle value.

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