News

Breaking the seal



30 November 2015

If you've ever had a long night out at the pub, you will have run across the strange phenomenon called 'breaking the seal'.
If you've ever had a long night out at the pub, you will have run across the strange phenomenon called 'breaking the seal'.

If you've ever had a long night out at the pub, you will have run across the strange phenomenon called 'breaking the seal'.

Yep, we're talking yellowish bodily fluids.

Your bladder holds up well until around the third (or fifth) drink. Then you just have to 'go' (and urinate). The timing goes like this - everything is fine until that third (or fifth) drink, and then you 'break' the magical 'seal'. For the rest of the night, you have to keep popping back to your new best friend, the toilet.

Of course, there is no special 'seal' keeping the urine inside your bladder - only your normal urinary sphincter.
The answer is straightforward.

Drink a six-pack, urinate a ten-pack.

Going deeper, there are two parts to the answer: physiology - alcohol makes you generate more urine than usual; and psychology - you drink a lot more liquid than usual.

As far as water is concerned, your body is a dynamic powerhouse. In each 24-hour day, about 50,000 litres of water crosses the many, many membranes in your body - and practically all of it (yep, 50 tonnes) crosses right back again. Only a few litres of liquid actually leave your body - as urine, water vapour from your mouth, sweat and so on.

They are replaced by water in the food you eat and in the liquids you drink. So there's a natural balance.

But alcohol interferes with the ability of your body to maintain this balance - and proper hydration. For every 200 mL of beer you drink, your kidneys generate 320 mL of urine. (So when I said "Drink a six-pack, urinate a ten-pack", I really should have said "Drink a six-pack, urinate a 9.6-pack" - but I figured it was OK to round up.) So when you guzzle down alcoholic drinks, you generate more urine than drinking the same amount of plain water.

Dehydration is quite serious - you can die of it. So your body has several mechanisms to keep you well hydrated.

One of these involves a hormone that confusingly has two common names - Vasopressin or ADH (Anti-Diuretic Hormone). 'Diuretic' just means related to urination. So the main job of ADH is to stop you from urinating.
Suppose you're lost in the desert and you run out of water. Your brain makes lots of ADH, and so you virtually stop making urine. That's a good survival tactic. But suppose you drink alcohol. The awkward side-effect of drinking alcohol is that your brain makes hardly any ADH, and so your kidneys start making lots of urine.

But the other factor related to 'breaking the seal' is simply volume. If you're heading for a Big Night Out, you're probably not going to drink half a dozen big glasses of water or milk. But you might easily drink half a dozen big glasses of beer.

So let's compare your bladder to a dried-out sponge.

Start dripping water onto this sponge, and for quite a while, it will just soak it up and store it. But eventually, the sponge will become totally saturated with water. Add just one more drop of water on the top of the sponge. Now a single drop of water will form on the bottom of the sponge. Add more drops, and a continuous trickle begins to form. At this stage, the 'seal' is broken.

Your bladder has a capacity of around 600-800 mL. But of course, you need to 'go' long before your bladder is completely full.

You throw down the first few beers pretty quickly. But remember, alcohol massively reduces your production of ADH. So for every 200 mL of beer you drink, your kidneys generate 320 mL of urine. By the time you get up to a litre of beer, you're getting a little dehydrated, and your kidneys will cut back a little - but overall, the volume of urine you generate is still greater than the volume of water contained in the beer.

So you do get slightly dehydrated, because you are urinating like crazy.
What if you drink lots of water to compensate for the extra volume of urine you generate? Your body will hang onto only about 30-50% of the extra water - the rest just goes down the toilet bowl. You end up better off than having not drunk the extra water - but you'll still be dehydrated.

The moral is quite straightforward - you don't buy beer, you only rent it. And it's very unlikely you'll ever regret not drinking too much.