Study finds novel mechanism that prevents overdrinking of water

By Jane Lewis
A swallowing inhibition mechanism appears to be activated after excess water has been drunk, helping maintain an appropriate fluid balance within the body, suggests an Australian study published in the Proceedings of the National Academy of Sciences.

Associate Professor Michael J. Farrell, Associate Director of Monash Biomedical Imaging at Monash University, Melbourne, and one of the authors of the paper, told Medicine Today that the over-arching message of the study was that it appears as though there are ‘good mechanisms in place to ensure we drink the right amount of water.’

‘If you try to drink in excess of that – for example, because you are attempting to comply with recommendations about water consumption, rather than because you are thirsty – you’ll probably find there is a lot of effort required to get the water down,’ he said.

For the study, functional magnetic resonance imaging (fMRI) was used to measure regional brain responses in 20 healthy participants (aged 23 to 45 years) who were asked to swallow small amounts of either water or a sugar solution, delivered in random order, under two different conditions: after exercise when thirsty and after drinking excess water. In addition, participants rated the effort required to swallow.

After overdrinking, participants reported a threefold increase in effort required to swallow (with little difference between water and sugar solution). fMRI showed the right prefrontal areas of the brain were much more active at this time, suggesting that an increase in goal-directed activity is required to overcome the swallowing inhibition.

‘The findings presented here support the view that swallowing inhibition is probably a “hardwired” process that successfully maintains fluid balance within the body, thereby avoiding the detrimental effects of overdrinking that can cause water intoxication and eventually death,’ the authors concluded.

Commenting on overdrinking in people under the influence of the drug ecstasy, Associate Professor Farrell suggested the hormone vasopressin may be involved. ‘We know from past research that brain regions involved in thirst are quite sensitive to vasopressin levels. Normally when you drink water, your vasopressin levels go down. It could be that when people using ecstasy drink water, the drug overrides that effect, and they don’t experience swallowing inhibition.’
Proc Natl Acad Sci USA 2016; 113: 12274-12279.

Picture credit: © Ivan Jekic/iStockphoto. Model used for illustrative purposes only.