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New study just further debunked the 8 glasses of water a day rule

Over-drinking is real.

FIONA MACDONALD
11 OCT 2016
 

For those of you who struggle to drink the advised eight glasses of water a day, we've got good news: a new study suggests that this 'rule' doesn't have to apply to everyone.

Instead, the research shows there's a simple way to figure out exactly how much water you need to drink each day - just listen to your body. 

 

That might sound pretty vague, but the researchers were able to show for the first time that when people no longer need to drink water, it physically becomes difficult to swallow. So, more specifically, listen to your throat.

This is the first time that the mechanism that regulates fluid intake and stops us from over-drinking has been identified, and it reinforces the fact that everyone's water needs are different.

"If we just do what our body demands us to we'll probably get it right - just drink according to thirst rather than an elaborate schedule," said lead researcher Michael Farrell from Monash University in Australia.

The good news is that even if you do drink eight glasses of water a day religiously, it's probably not going to do you any harm - some people might need more than that, and some people might need less.

But with that in mind, we know when we need to drink more water because we're thirsty, so how do we know when we've had enough?

Over-drinking is actually a real problem, and can lead to something called water intoxication - or hyponatremia - which is where sodium levels in the bloodstream become abnormally low, and can lead to everything from lethargy and nausea to seizures, coma, and even death.

 

But until now, no one had figured out how the body regulated this, and whether there was a hard-wired response to stop us from drinking too much water.

To investigate, Farrell and his team asked 20 participants to rate the amount of effort it took to swallow water under two conditions: after exercise when they were thirsty, and then later on when they were persuaded to drink an excess amount of water.

The team found that there was a three-fold increase in effort after people had drunk too much water - a sign that the body was regulating how much water it consumed by making it physically harder to drink. 

"Here for the first time we found effort-full swallowing after drinking excess water which meant they were having to overcome some sort of resistance," said Farrell. "This was compatible with our notion that the swallowing reflex becomes inhibited once enough water has been drunk."

The team also used functional magnetic resonance imaging (fMRI) to measure activity in the brain just before people drank water under these two conditions, and when they were over-drinking, there was a lot more activity in the right prefrontal areas of the brain.

That suggested that the frontal cortex was stepping in to override the hard-wired swallowing inhibition, so that the participants could drink as much water as the researchers required.

The study definitely has its limitations - it was a small sample size, and not only was the swallowing inhibition mechanism self-reported, it also wasn't correlated with sodium levels in the bloodstream to confirm that it was being triggered by over-drinking.

But it's a positive first step in beginning to understand how our bodies control fluid intake, and it could help people make better choices about drinking - particularly if they're often struggling to meet daily requirements and forcing themselves to swallow down enough water.

"There have been cases when athletes in marathons were told to load up with water and died, in certain circumstances, because they slavishly followed these recommendations and drank far in excess of need," said Farrell.

But he also noted that elderly people in particular often don't drink enough, so should be mindful of their fluid intake.

More research is now needed to confirm these results and verify that the swallowing inhibition response is a result of over-drinking, but in the meantime, it's a good idea to stay hydrated, but listen to your body. If it really doesn't want to swallow any more water, it might be onto something.

The research has been published in the Proceedings of the National Academy of Sciences.

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