main article image
(iStock)

How Many Glasses of Water a Day You Really Need, According to Science

There is such a thing as too much water!

FIONA MACDONALD
21 FEB 2018
 

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

Instead, a compelling 2016 research paper shows there's a simple way to figure out when you've had enough - just listen to your body. 

 

That might sound pretty vague, but a team of researchers from Monash University in Australia has showed that when people no longer need to drink water, it physically becomes difficult to swallow.

So, more specifically, listen to your throat. This handy built-in mechanism 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.

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.

 

In the study, 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.

 

We're only just starting to understand how our bodies control fluid intake, but this kind of research might 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.

Really, when it comes to the eight glasses of water a day myth, 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 was published in the Proceedings of the National Academy of Sciences.

 

More From ScienceAlert

Neanderthals may have used their stone tools to start fires

We really don't give those guys enough credit.

15 hours ago