Will coffee dehydrate you?

Will coffee dehydrate you? If you are concerned about the detrimental effects of coffee on your hydration status, this article is for you.

Definitions

• coffee (noun): a beverage made by percolation, infusion, or decoction from the roasted and ground seeds of a coffee plant (1)
• caffeine (noun): a bitter alkaloid C₈H₁₀N₄O₂ found especially in coffee, tea, cacao, and kola nuts and used medicinally as a stimulant and diuretic (2)
• diuresis (noun): an increased excretion of urine (3)

How much caffeine is in coffee?

The amount of caffeine in coffee drinks is highly variable. For example, the following have been found to affect how much caffeine is in brewed coffee: species (i.e. Robusta vs Arabica), temperature of brewing water, coffee to water ratio, volume of coffee drink, origin of coffee beans and method of growing, among other factors (4).

The table below shows some averages based on Australian data (5):

• Short black (espresso takeaway cup): ~145mg
• Long black (regular takeaway cup): ~163mg
• Flat white/latte (regular takeaway cup): ~159mg
• Cappuccino (regular takeaway cup): ~198mg
• Mocha (regular takeaway cup): ~156mg
• Instant coffee (regular takeaway cup): ~87mg
• Cola soft drink (375ml can): 39-41mg
• Energy drink (250ml): 58-84mg

However, actual values in your coffee can be all over the place. For example, reported ranges include 25-214mg per espresso (6) and 95–165mg per coffee drink (7).

Why focus on coffee?

Although caffeine is present in other beverages and foods, coffee is likely the most commonly consumed in Australia and other countries.

Moreover, there are some health benefits associated with coffee consumption, which is why many people are encouraged to drink it. In addition, caffeine can improve performance.

Will coffee dehydrate you?

While many people say the answer is yes, the truth is it depends. There is variability within results of studies that have investigated this topic. This is likely partially due to individual differences in genes and caffeine metabolism.

The general trends are:

• Lower doses of caffeine from coffee (either less than 300mg/day or 5mg/kg per day) doesn’t seem to increase diuresis (7, 8)
• Higher doses of caffeine (either more than 500mg/day or 6mg/kg/day) increase diuresis and can lead to a significant loss of body water (7)
• Exercise decreases diuresis, reducing the effect of pre-exercise ingested caffeine (7, 8)
• The effects of caffeine from coffee on diuresis are larger in females than males (8)
• The effects of caffeine on diuresis are smaller in individuals who are usual caffeine users (6)

But water out (in urine) is only part of the equation. You need to consider that there is fluid in a coffee beverage, either if you drink it black or with milk. In practice, the net fluid balance is not likely to be negative unless you are drinking supernormal amounts of coffee, or you have a health condition that makes you produce abnormal amounts of urine.

Summary and recommendations

• The amount of caffeine in coffee is highly variable, making it difficult to establish a limit of beverages that may increase diuresis
• The amount of caffeine in coffee is highly variable, making it difficult to use coffee as a controlled source of caffeine for athletic performance
• The effect of caffeine in diuresis depends on genetics, gender, usual caffeine intake, body weight and whether it is taken prior (or during) exercise
• If your coffee intake is large enough that you notice a significant effect on urine production and/or you are dehydrated for other reasons, ensure you are taking in sufficient fluids (with meals and/or with the addition of electrolytes)
• Last but not least, this article is about coffee and diuresis. Caffeine consumption can have detrimental effects on some aspects of health (for example, sleep) so consider the whole picture before making decisions on your intake

References

1. “Coffee.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/coffee. Accessed 14 Oct. 2023.
2. “Caffeine.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/caffeine. Accessed 14 Oct. 2023.
3. “Diuresis.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/diuresis. Accessed 14 Oct. 2023.
4. Olechno E, Puścion-Jakubik A, Zujko ME, Socha K. Influence of Various Factors on Caffeine Content in Coffee Brews. Vol. 10, Foods. 2021.
5. Food Standards Australia New Zealand. Australian Food Composition Database – Release 2​​ [Internet]. Canberra; 2022. Available from: https://www.foodstandards.gov.au
6. Burke, L., Deakin, V. EBOOK Clinical Sports Nutrition 5e, 5th Edition. McGraw-Hill Australia; 20150918. Retrieved from vbk://978174376312420150918.
7. Seal AD, Bardis CN, Gavrieli A, Grigorakis P, Adams JD, Arnaoutis G, et al. Coffee with High but Not Low Caffeine Content Augments Fluid and Electrolyte Excretion at Rest. Front Nutr. 2017;4:40.
8. 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 Sep;18(5):569–74.

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