Bottles of alcohol behind a bar helping to illustrate the kind of drinking that leads to dehydration

How do Alcohol and Caffeine Affect my Hydration?

October is a busy month. Halloween is right around the corner and before it’s even out of the way, shops are already stocking up with mince pies.

Of course, in more recent years, October has also been associated with Breast Cancer Awareness month, ADHD Awareness month and National Cholesterol month, although the list doesn’t stop there.

Unless you’ve been a bit out of touch with social media recently, likely chances are you’ve heard about ‘Go Sober for October’. But just in case you haven’t, the campaign was started by Macmillan Cancer Support to help raise money for people living with cancer and encourages people to give up alcohol for all of the 31 days in October.

So with a countless number of people giving up alcohol this month for a fantastic cause, we at Aquarate HQ, wanted to know more about how drinking alcohol might affect hydration.  After all, we’ve probably all heard that alcohol can lead to dehydration at some stage in our lives. But how?

Firstly, our kidneys help control the amount of water in our bodies through monitoring the plasma osmolality within our blood. This means keeping track of the concentration of particles, such as mineral salts, sugars, and water, to name a few.  It is our kidneys that can block or allow certain particles into our urine to maintain balance within our bodies. However, alcohol can upset this balance, causing us to lose necessary water. 

Of course, it’s also widely recognised that alcohol is a diuretic. Or for those of us who don’t remember our biology lessons at school, alcohol makes you want to use the toilet more.

In other words, alcohol reduces the production of the antidiuretic hormone – Vasopressin – which the body uses to reabsorb and hold onto water. With less antidiuretic hormone, the body is able to lose more water through increased urine output. 

Interestingly, studies have shown that drinking wine and spirits increases urine output more than beer due to the lower percentage of alcohol found in beer (Polhuis et al., 2017).

Did you know that for every 10g of alcohol you drink, urine output increases by 100mL?

(Eggleton, 1942)

Research also shows that alcohol is only one of 2 diuretic agents found in the modern diet (Hobson & Maughan, 2010). The second belongs to the methylxanthine family and is otherwise called – you guessed it – caffeine!

But before we start worrying about that morning cup of coffee, caffeinated drinks have only been reported to have a mild diuretic effect, which means moderate caffeine consumption may cause us to use the toilet more, but doesn’t seem to increase the risk of dehydration. Or to put it another way, that cup of tea or coffee gives us more water than we might lose from the effects of caffeine.

In fact, the NHS noted from a 2014 study, that there was no significant difference in hydration levels between those who drink coffee, and those who drink water. 

However, the sample size was small (50) and only used healthy men. It is difficult to know what differences there would be – if any – had the study been carried out with women. It should also be pointed out that the men in the study were used to drinking at least 3 to 6 cups of coffee per day, so may have built up a tolerance. 

So overall this study could be considered good news for us British folk who enjoy a cup of tea or coffee! But do be aware that decreased kidney function could impact how much caffeine a person should drink. 

Fun fact: During WW2, Britain bought all the tea in the world! It was to help keep up morale.

(Keen, 2016)

So what are the take home points?

Like most things in life, moderation is key! Height, weight, and gender all have a role to play, so always know your limits.

If you enjoyed this blog post, we’d love to hear from you! Please comment below with any thoughts or tips you may have to help stay hydrated during the day or on a night out.


Eggleton, M G. “The diuretic action of alcohol in man.” The Journal of physiology, Volume 101, Issue 2, 1942, Pages 172-91. Available at: 

Hobson, R.M. and Maughan R.J, “Hydration Status and the Diuretic Action of a Small Dose of Alcohol”, Alcohol and Alcoholism, Volume 45, Issue 4, July-August 2010, Pages 366–373. Available at: 

Keen, P.G.W., “The year Britain bought up all the tea in the world”, Teabox, 2016. Available at:

NHS, “A small amount of coffee will not dehydrate you”, 2014. Available at:

Polhuis, K.C.M.M., Wijnen, A.H.C., Sierksma, A., Calame, W. and Tieland, WM, “The Diuretic Action of Weak and Strong Alcoholic Beverages in Elderly Men: A Randomized Diet-Controlled Crossover Trial.” Nutrients, Volume 9, Issue 7: 660. 28 Jun. 2017. Available at:

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