Does too much caffeine cause dehydration?

March 25, 2019 4 min read

Does too much caffeine cause dehydration?

Achieving a healthy disposition and well-being can be as simple as keeping yourself hydrated.

Can’t put two and two together?

Studies show that poor hydration leads to poor health. [1] In fact, dehydration can have an adverse impact on mood, brain and cardiovascular functions and has been “associated with poor outcomes” among hospitalized elderly. [2, 3]

(If you want to learn more about dehydration, check out this article: Dehydration: causes, signs, and symptoms)

So what does this mean for coffee-lovers and caffeine junkies?

Some people say that caffeine can make you dehydrated.

But is there any truth to this? Or is it just another #fakenews alert?


Does caffeine cause dehydration?

The idea that caffeine intake causes dehydration can be traced back to a 1928 study. It noted increased urination in people who drank beverages with caffeine in them.

But drinking any beverage in larger volumes, with or without caffeine, causes you to urinate more. And this includes water itself.


One of the reasons why caffeinated drinks like coffee, tea, soda, and energy drinks, have been infamously known for causing dehydration is this:

Caffeine is a diuretic, especially when consumed in over 500 mg. [4]

Diuretics make you pee more. This means that not only do they make you go to the toilet more, they also bring down your sodium and water levels, which may have adverse effects on your body temperature and food absorption. 


So if you’re starting to worry that your daily caffeine fix will lead to this, hold your horses.

The amount of caffeine in a regular cup of coffee or tea would barely cause dehydration. In fact, the opposite happens – drinking a cup of joe adds to your daily fluid intake. 


Dry mouth syndrome

Another reason why some may think caffeine causes dehydration is how dry it makes their mouth feel after drinking coffee.

According to Ali Webster, PhD, RD, and associate director of nutrition communications at the International Food Information Council Foundation (IFIC), this may be because of tannins, compounds found in caffeinated products.

When tannins bind to the saliva, they give off that “drying, astringent feeling.” [5]


Caffeine does NOT cause dehydration

But as it turns out, caffeine causing dehydration is nothing but an urban legend.

While caffeinated products may have a mild diuretic effect, they don’t lead to dehydration. In fact, they can contribute to your overall daily water needs.

But it won’t send you more times to the toilet than any other drink.


According to Lisa Renn, accredited practicing dietitian and spokesperson for the Dietitians Association of Australia: [4]

"There is evidence that caffeine in higher amounts acts as a diuretic in some people, but moderate intake is actually not that significant.” 


Supporting studies

Here is some scientific evidence that caffeine (and coffee) does NOT result in dehydration:

In 2005, Lawrence Armstrong, a professor in the Department of Kinesiology at the University of Connecticut and director of the Human Performance Laboratory, did a longer-term study. [6]

Dr. Armstrong and his team gave 59 healthy males a controlled diet for 11 days. Each man got doses of caffeine commensurate with their body mass. The caffeine came in capsules, twice a day. The team studies what Live Science calls 20 hydration biomarkers, including urine volume and fluid-electrolyte balance to measure any possible dehydration. Live Science reported: [6]

The study found that the evaluated hydration indicators, including urine volume, were similar for all of the treatment groups. This finding demonstrates that caffeine does not have a dehydrating effect when compared to the control group (participants who received a placebo and did not consume any caffeine). The scientists also found that a higher dose of caffeine was no more likely to dehydrate a person than smaller doses were.

And as Dr. Armstrong aptly explained:

The fact that we don't have hospital emergency rooms filled [with patients] because they [drank] caffeinated beverages is clear evidence ... If there were negative health effects, [they] certainly would have been identified.


According to Mayo Clinic, "drinking caffeine-containing beverages as part of a normal lifestyle doesn't cause fluid loss in excess of the volume ingested." The study noted: [4

    While caffeinated drinks may have a mild diuretic effect, meaning that they may cause the need to urinate, they don't appear to increase the risk of dehydration.


    A 2014 article on BBC reports a study that found no difference in hydration levels between water and coffee: [7]

    A second study found no difference in hydration between those drinking water or coffee, leaving us with conflicting findings. Then came new research earlier this year from Sophie Killer at Birmingham University in the UK, who not only measured the volume of urine, but tested their blood for signs of kidney function as well as calculating the total amount of water in the body. The men in the study drank four cups of coffee a day, far more than the average coffee-drinker. Yet there was no evidence they were any more dehydrated than those who drank water alone. This research was funded by the Institute for Scientific Information on Coffee, whose members are coffee companies, but it has been published in a peer-reviewed journal and the authors confirm that the Institute played no role in gathering or analysing the data or writing up the research.



    While caffeine has a mild diuretic effect, it does NOT cause dehydration. It may make you use the loo more frequently, but not more than any other drink. And neither will it impact your body’s sodium levels and water volume.

    So fret not – you can still have your daily cup of joe and still be your most hydrated you!

    Tina Sendin
    Tina Sendin

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