Monash University
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.
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 institutes.
"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' instructions.
"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 said.
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.
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 Proceedings of
the National Academy of Sciences. It was carried out in collaboration with
the Florey Institute of Neuroscience and Mental Health, University of Melbourne
and Baker IDI & Diabetes Heart Institute.
