Drinking too much water in the body puts it in danger of water
intoxication or hyponatremia, when vital levels of sodium in the blood
become abnormally low potentially causing symptoms ranging from lethargy
and nausea to convulsions and coma.
A multi-institute study led by Monash University has revealed for the
first time the mechanism that regulates fluid intake in the human body
and stops us from over-drinking, which can cause potentially fatal water
intoxication. The study challenges the popular idea that we should
drink eight glasses of water a day for health.
‘A 'swallowing inhibition' is activated by the brain after excess liquid is consumed, helping maintain tightly calibrated volumes of water in the body.’
The study showed that a 'swallowing inhibition' is activated by the
brain after excess liquid is consumed, helping maintain tightly
calibrated volumes of water in the body.
Associate Professor Michael Farrell from the Monash Biomedicine
Discovery Institute oversaw the work by University of Melbourne PhD
student Pascal Saker as part of a collaboration with several Melbourne
"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," Associate Professor Farrell said.
Building on a previous study, the researchers asked participants to
rate the amount of effort required to swallow water under two
conditions; following exercise when they were thirsty and later after
they were persuaded to drink an excess amount of water.
The results showed a three-fold increase in effort after over-drinking.
"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," Associate Professor Farrell said. "This was compatible with our notion that the swallowing reflex becomes inhibited once enough water has been drunk."
Associate Professor Farrell, who works in the Monash University
Department of Medical Imaging and Radiation Sciences, used functional
magnetic resonance imaging (fMRI) to measure activity in various parts
of the brain, focusing on the brief period just before swallowing.
The fMRI showed the right prefrontal areas of the brain were much
more active when participants were trying to swallow with much effort,
suggesting the frontal cortex steps in to override the swallowing
inhibition so drinking could occur according to the researchers'
"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," he
Associate Professor Farrell said elderly people, however, often didn't drink enough and should watch their intake of fluids.
The study, 'Overdrinking results in the emergence of swallowing inhibition: an fMRI study'
is published online in the journal Proceedings of the National Academy of Sciences
in the United States of America. It was carried out in collaboration
with the Florey Institute of Neuroscience and Mental Health, University
of Melbourne and Baker IDI & Diabetes Heart Institute.