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Does Coffee Dehydrate You? - Coffee Quiz

For several decades until recently, since a study in the late 1920s, many believed coffee to cause dehydration even when consumed in small amounts. 

But what if I told you that this particular study was conducted with only three participants?

Does Coffee Dehydrate You? - Coffee Quiz

And what if I just happened to mention that the conclusion wasn’t reached by measuring dehydration but just the slightly increased amount of urine produced after drinking the beverage?

Would you still believe the study to be valid?

Personally, I would still have my doubts. So, I did some more research.

Thankfully, there are many studies that have taken interest in the same topic!

Coffee and its benefits

Before diving into how that study came to pass as a common belief and how coffee affects the hydration of your system, let’s talk for a second about coffee as a beverage.

Due to its misunderstood reputation, it is not uncommon for all the benefits of this drink to escape one’s notice most of the time.

Coffee, often only considered a mere caffeine vehicle, has a lot of nutritional value to offer as well.

See, coffee is a beverage that contains a lot of micronutrients beneficial to the human body, from essential vitamins to antioxidants and minerals like magnesium and potassium.

These nutrients have been linked to a healthy diet, and some of them are great for tuning your system as a whole.

It has also been linked to combating illnesses like type 2 diabetes, nervous system degenerative diseases (Parkinson’s and Alzheimer's), and some kinds of cancer. (Click here to read more about coffee and cancer.)

And these benefits remain regardless of the caffeine content of your drink. Both normal and decaf will have those advantages for your organism!

At least when drunk in moderate amounts! (3-5 cups a day).

Japanese coffee cup

Coffee as a diuretic

Now that we've mentioned caffeine, of course, I think it’s high time we dove more into the main subject of this post, which is coffee’s association with dehydration.

Caffeine is, among other things, a diuretic. This means that it sends more blood to your kidneys, making them release more water from your body after consumption.

Remember that one study we spoke of earlier?

That’s exactly where the researchers based their conclusion.

What they didn’t consider, however, even in their small participant population, was that the net fluid loss after coffee’s consumption wasn’t negative overall.

And it must also be mentioned that the urine increase occurred only when the participants abstained from coffee (and all drinks containing caffeine, for that matter) for more than 60 days.

When their bodies were used to it, usually after just a few days, the diuretic effect vanished.

Additives and their effects for Infrequent drinkers

Speaking of net fluid loss, we have to take other elements into account, like additives inside your cup.

There is an exceptionally wide variety of coffees one can make or find in the market. And a lot of different additives, from sweeteners and milk to alcohol, that should by no means be forsaken.

As a cup of coffee isn’t just caffeine, micronutrients, and water but also everything else we use to alter its taste and mouthfeel, we have to consider how this might affect our body, combined with caffeine’s diuretic effect.

For infrequent drinkers, while black coffee or coffee with milk is of absolutely no harm, sweeteners and excess sugar amounts can do some damage.

While a small amount, like a couple of teaspoons, is harmless, there are coffee beverages on the market that also contain a lot of syrup as well as added sugar.

black coffee

Decaffeinated coffee and Dehydration

Decaffeinated coffee is, in many cases, an exception among coffees.


Dehydration isn’t one of them.

Normal coffee doesn’t dehydrate you in average (or even large) amounts. It just isn’t enough to tip the balance of fluids in your system.

If your diet already doesn’t contain enough liquids or nutrients and you consume a very large amount of caffeinated, very high-sugar coffee, then yes, you might experience some mild dehydration.

But decaf is completely devoid of that problem because it has no diuretic effect whatsoever.

Of the chemicals inside decaf, there are none that could cause your body to lose water, let alone to a dehydrating degree!


To answer the initial question…

No, coffee does not dehydrate you!

When drank in moderate or even large amounts by frequent drinkers, it has no negative impact on your hydration at all.

When you are an infrequent drinker, it will probably cause you to want to visit the restroom a bit more often, but the total amount of liquid excreted is just slightly higher than if you were drinking water.

Decaffeinated coffee has no impact either because none of its chemicals affect your body’s hydration in a negative way. If anything, it is beneficial for your body with all its micronutrients and antioxidants.

That said, it is important that you keep sweeteners in mind, as they are known for their dehydrating effect in excess amounts. If you pair them up with the diuretic effect, it could definitely destabilize your body.

Overall, hydration comes down to your own diet and lifestyle. Your daily cup of joe isn’t going to change that!

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Japanese Coffee Blog is a collection of articles related to the Japanese Coffee and Charcoal Roasted Sumiyaki coffee which is unique roasting only found in Japan. Coffee culture in Japan has evolved isolated from around the world and has much uniqueness not found in the rest of the world.

Authored by popular Japanese Tea Blogger Kei Nishida, he hopes to reveal the wonderful world of Japanese coffee from a different angle to educate and entertain people who love Japan, Japanese Tea, and now Japanese Coffee.

Author: Kei Nishida

Kei Nishida

Kei Nishida is a writer, a Japanese Green Tea and Coffee enthusiast, and the founder and CEO of Japanese Green Tea Company and Japanese Coffee Company.

His popular Japanese Green Tea and Health Blog has been the go-to place for anything related to Japanese tea.

He is an author of multiple books, and you can find his work in multiple publications and magazines.

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