Does drinking alcohol actually cause dehydration?


Today I came across this article: Drinking water doesn’t prevent a hangover, study says, which includes the memorable line: “[the] study concluded, the only way to prevent a hangover is to drink less alcohol.”

Now, at first sight, you might think that surely this simply another piece of work from the University of the Bleedin’ Obvious.

But hang on. Alcohol does dehydrate you, doesn’t it? Everyone knows that! After all, don’t you wee more when you go drinking, and wake up all sweaty and with a dry mouth after a ‘heavy night’? Surely this is all evidence of fluid loss? Am I really about to suggest we should consign ‘alcohol causes dehydration” to the collection of alcohol-based myths such as mixing drinks gives you a worse hangover (only if you drink more as a result), a night cap will help you sleep (only temporarily, overall it tends to disrupt sleep), drinking beer will cause a ‘beer belly’ (too much of any type of drink can cause weight gain), and so on?



There are many alcohols; ethanol is the one we drink.

Firstly, what is alcohol or, more specifically (the word ‘alcohol’ actually refers to a group of compounds), ethanol? It’s a simple molecule, containing only two carbon atoms, an oxygen and some hydrogen atoms. It’s produced, as we all learned at school (or possibly when attempting home-brewing), by yeast during the process of fermentation. Feed this clever little single-celled organism some sugar and voilà, it produces ethanol (C2H5OH) and carbon dioxide via a remarkably simple equation:

C6H12O6 –> 2C2H5OH + 2CO2


Marula fruit naturally ferments.

Humans learned this trick a long time ago and have been brewing for literally thousands of years. In fact it doesn’t even require human intervention – marlula fruit is particularly famous for becoming naturally alcoholic (although stories of monkeys and elephants using it to get drunk might be somewhat exaggerated).

We like drinking because, of course, of what it does to us. In medical terms, it’s a central nervous system depressant with significant psychoactive effects (sounds fun, eh?) In English, it reduces anxiety, making drinkers feel relaxed and happy. This accompanies a decrease in motor skills of course, which is why drinking and driving is illegal virtually everywhere (although exact definitions of what this means do vary).

But while alcohol is all natural, it’s not what you’d consider healthy. Every now and then someone drags out some data that suggests that low to moderate alcohol intake is good for you, but this sadly appears to be more wishful thinking than good science. In terms of disease, alcohol consumption has been linked with stroke, high blood pressure, several liver diseases, pancreatitis, a weakened immune system and a handful of cancers including mouth, throat, liver and breast cancers.

In fact, alcohol has been categorised by the International Agency for Research on Cancer as a group 1 carcinogen, which puts it in the company of such other delights as asbestos, radium isotopes, ultraviolet radiation, diesel exhaust and tobacco.


Give up alcohol before you worry about your latte ingredients.

Of course, the dose makes the poison. Lots of people enjoy low to moderate alcohol consumption quite safely. Still, I have to admit to being amused by health nuts that insist on a diet consisting of little more than raw vegetables, make a fuss about so-called GMOs, campaign for additives (none of which are anywhere close to being group 1 carcinogens) to be removed from food, and then post pictures of themselves drinking wine. You really want to improve your health? Never mind caramel colour IV in your latte, give up the booze.

So, alcohol isn’t a health food, or indeed drink. But to get back to the original question, does it cause dehydration? Well, it would appear that while it does do a lot of bad stuff health-wise, that’s not one of the bad things it does. In a study, men drank six pints of beer and were then subjected to a number of tests. As the subsequent PubMed article states: “All subjects had a slight hangover, but none was fluid depleted”.

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Twin doctors Chris and Xand van Tulleken in a recent BBC documentary.

In a recent BBC Horizon documentary, twin doctors Chris and Xand van Tulleken collected all their urine during a night in which Xand drank 21 units of alcohol in one sitting (while his brother only had one drink), and next morning demonstrated that the volumes were the same. In other words, the excessive alcohol consumption had not, as is widely believed, had a significant diuretic effect.

Admittedly, this was only two people, and the PubMed study only involved six participants – small sample size is often an issue with such work. The Dutch study I mentioned at the start was much larger, which is one reason it’s useful. In that study, drinking water appeared to make little difference to the severity of the hangover experienced. The only thing that really mattered was, not surprisingly, how much alcohol had been consumed.

In fact it’s not well-understood what does cause hangovers. It would appear it’s linked to an immune system response. In very simple terms, getting blind drunk is a little like self-imposed flu. Drinking plenty of fluids won’t do you any harm, but it’s not actually a solution. Of course, there’s no virus involved here to keep the immune system on the warpath, so for most healthy people the best, and probably only, hangover cure is time.

So in summary, yes, we probably can chuck “alcohol causes dehydration” in with all the other alcohol myths floating around out there, but that’s not an excuse to have a pint after your workout.

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The Chronicle Flask’s festive chemistry quiz!

Tis the season to be jolly! And also for lots of blog posts and articles about the science of christmas, like this one, and this one, and this one, and even this one (which is from last year, but it’s jolly good).

But here’s the question: have you been paying attention? Well, have you? Time to find out with The Chronicle Flask’s festive quiz! I haven’t figured out how to make this interactive. You’ll have to, I don’t know, use a pen and paper or something.

Arbol_de_navidad_con_adornos_de_personajesQuestion 1)
Which scientist invented a chemical test that can be used to coat the inside of baubles with silver?
a) Bernhard Tollens
b) Karl Möbius
c) Emil Erlenmeyer

Question 2)
Reindeer eat moss which contains arachidonic acid… but why is that beneficial to them?
a) a laxative
b) an anti-freeze
c) a spider repellant

1280px-ChristmasCrackers_2Question 3)
Which chemical makes crackers and party poppers go crack?
a) gunpowder
b) silver fulminate
c) nitrogen triiodide

640px-Glass_of_champagneQuestion 4)
We all like a glass of champagne at this time of year, but what’s in the bubbles?
a) carbon dioxide
b) nitrogen
c) oxgyen

Question 5)
What’s the key ingredient in those lovely bath salts you bought for your grandma?
a) calcium carbonate
b) magnesium sulfate
c) citric acid

The Bird - 2007Question 6)
Which chemical reaction is responsible for both perfectly browned biscuits and crispy, golden turkey?
a) Maillard reaction
b) Hodge reaction
c) Caramel reaction

Question 7)
Sucrose-rodmodelWhere are you most likely to find this molecule at this time of year?
a) in a roast beef joint
b) in the wrapping paper
c) in the christmas cake

Question 8)
Let it snow, let it snow, let it snow… but which fact about (pure) water is true?
a) It glows when exposed to ultraviolet light
b) It expands as it freezes
c) It’s a good conductor of electricity

Ethanol-3D-ballsQuestion 9)
Where are you likely to find this molecule on New Year’s Eve?
a) in a champagne bottle
b) in the party poppers
c) in the ‘first foot’ coal

OperaSydney-Fuegos2006-342289398Question 10)
Who doesn’t love a firework or two on New Years Eve?  But which element is most commonly used to produce the colour green?
a) magnesium
b) sodium
c) barium

(Answers below…)

1a) Bernhard Tollens (but his science teacher was Karl Möbius).
2b) It’s a natural anti-freeze.
3b) Silver fulminate (it always surprises me how many people guess gunpowder. That would be exciting).
4a) carbon dioxide.
5b) magnesium sulfate which, funnily enough, also causes ‘hard’ water.
6a) the Maillard reaction, although Hodge did establish the mechanism.
7c) In the cake – it’s sucrose (table sugar).
8b) it expands as it freezes and is thus less dense than liquid water (which is why ice floats). We take this for granted, but most things contract (and become more dense) as they turn from liquid to solid. You should be grateful – live probably wouldn’t have evolved without this peculiar behaviour.
9a) In the champagne – it’s ethanol (or ‘alcohol’ in everyday parlance).
10c) barium – copper produces green flames too, but barium salts are more commonly used in fireworks.

So how did you do?
Less than 4: D, for deuterium. It’s heavy hydrogen and it’s used to slow things down. Enough said.
4-6: You get a C, by which I mean carbon. Have another slice of coal.
7-8: You’ve clearly been paying attention. B for boring, I mean boron.
9-10: Au-ren’t you clever? Chemistry champion!

Happy New Year everyone! 🙂

Are you a Christmas chemist and you didn’t know it?

So Christmas has been and gone and we’re all forlornly looking at pine-needles around the tree and the mountainous pile of recycling in the kitchen, promising ourselves that we’ll eat nothing but salad come January first. But in the meantime, let’s take a bit of time out from the sales, watching Christmas telly and eating endless chocolates (I’m pretty sure anything eaten between December 24th-31st doesn’t count) and think about all the chemistry we’ve done over the last few days – yay!

Cracker snaps contain silver fulminate.

Cracker snaps contain silver fulminate.

Pulling crackers
Pulled a cracker over Christmas? Of course you have, and probably more than one. Did you wonder what caused the bang and the strangely appealing chemically smell? Of course you didn’t, but never fear, I shall tell you anyway. It was probably silver fulminate, AgCNO. This particular chemical is a primary explosive, but not a particularly useful one due to its extreme sensitivity. It’s so sensitive to any kind of shock (including the touch of a feather, a drop of water, or even just a particularly loud noise) that it’s completely impossible to collect more than the most minute amount without it blowing up unexpectedly. It was first prepared by Edward Charles Howard in 1800, who was working on preparing fulminates. None of them are stable, and one has to wonder if he had any eyebrows or eardrums by the time he’d finished. Anyway, silver fulminate has found one sort of practical use, and that’s in novelty snaps like the ones in crackers. There’s a tiny amount of silver fulminate on one piece of cardboard, and an abrasive on the other. When you pull, the two rub against each other and BANG! Paper hats, plastic toys and bad jokes abound. What happened after an explosion at a French cheese factory? All that was left was de brie.

Release the pressure and carbonic acid converts into water and carbon dioxide. Quickly.

Release the pressure and carbonic acid converts into water and carbon dioxide. Quickly.

Opening bottles of fizzy stuff
Most people are probably already vaguely aware that the bubbles are carbon dioxide, but there’s more to it than that, oh yes. Have you ever noticed that the liquid in the bottle looks completely bubble-less until you actually open it? If not, check next time. It’s really quite amazing. Why is this? Well, there’s a bit of chemistry going on. Brace yourself for an equation:

CO2 + H2O ⇌ H2CO3

There on the left you have carbon dioxide and water, and on the right something called carbonic acid. The double arrow thingy means the reaction is reversible, and the thing about reactions like this is that they will sit there quite happily, perfectly balanced, until something happens to change them. In the case of fizzy bottles, opening them will do that. It lets out the carbon dioxide and that causes the reaction to make yet more water and carbon dioxide in an attempt to compensate. That’s where all the bubbles come from, and it’s also why fizzy drinks taste peculiarly sweet if they’re left to go flat – like all acids (testing this is not recommended, but trust me) carbonic acid tastes sour and when it gets used up the sweetness due to sugars and sweeteners starts to take over. Contrary to popular belief, putting a spoon in the bottle will do absolutely nothing whatsoever to stop your champers from going flat. Sticking some kind of air-tight stopper in it, on the other hand, will definitely help.

The blue flame is due to complete combustion.

The blue flame is due to complete combustion.

Setting fire to the christmas pudding
Or rather, the generous splash of alcohol you’ve just poured on it. Have you noticed that the flame is a lovely blue colour, very different from the warm yellow of coal and candles? That’s because when you burn alcohol, specifically ethanol, CH3CH2OH, you get something called complete combustion. This happens when there’s enough oxygen to only produce carbon dioxide and water as products. Ethanol has an oxygen atom built in, so it burns more completely than hydrocarbon fuels like coal and candle wax, which tend to produce carbon atoms (also known as soot) and carbon monoxide as well. The reason the flame is blue rather than yellow is because that yellow colour is caused by carbon atoms getting so hot that they glow. By definition, in complete combustion there’s no carbon, so no yellow. Instead the gas molecules in the flame get so hot they start glowing instead, giving off blue light. All together now, oooooh!

Alpha-pinene gives christmas trees their smell.

Alpha-pinene gives christmas trees their smell.

Sniffing a Christmas tree
What is that lovely smell? Mostly a molecule called pinene, specifically alpha-pinene. It’s a funny-looking thing isn’t it? Looks a bit like a waiter rushing with a full drinks tray. Anyway, there are two forms of this molecule: alpha and beta.  Alpha is the most common one in nature, particularly in conifers (which Christmas trees are). Peculiarly, it somehow manages to be both an insect repellant while also, apparently, being used by insects as a chemical communication system. I don’t know how this works, ask an entomologist.

Christmas lights owe their glow to tungsten.

Christmas lights owe their glow to tungsten.

Switching on the Christmas lights
These days, LED lights are slowly taking over, but there are still enough filament bulbs kicking around in boxes of decorations that they’ll probably persist for a few years yet. Electricity consumption be dammed, they do make a much prettier glow. And why is that? It’s partially due to tungsten, element number 74. It has the highest melting point of all the elements (there’s a handy fact for your next trivia quiz) and as a result it is, or at least used to be, used to make the filament in incandescent light bulbs. Heat it up and it starts to glow long before it reaches its melting point of 3422 oC. The bulbs are also filled with an inert gas, usually krypton (nothing whatsoever to do with Superman, sorry), which stops the tungsten from reacting with the oxygen that would be present in ordinary air. In fact, filling a bulb with krypton makes it even brighter and longer-lasting than just pumping all the air out leaving a vacuum, because the krypton helps to disperse the heat.

So there you go, just a few of the many, many bits of chemistry you’ve done so far this Christmas. Enjoy the rest of the chocolates, have a happy New Year, and to those out there with January mock exams coming up, good luck!