Can you drink too much water? fMRI research says you can

Many of us struggle to drink the recommended eight glasses of water per day, but a new study using fMRI suggests that we're not supposed to.

The study, led by researchers at Monash University in Australia, found the mechanism in the body that regulates fluid intake stops humans from over-drinking.

The response to over-drinking is an activation of swallowing inhibition. The researchers, guided by Michael Farrell, PhD, MSc, found that when the body has consumed enough liquid, it will naturally make it more difficult to consume anymore.

In the study, participants were asked to rate the amount of effort required to swallow water under two conditions—following exercise and later after the workout when asked to drink water in excess. Results showed that it was three times more difficult for participants to drink water under the second condition when time had passed between working out and drinking more water, showing that the swallowing reflex becomes inhibited once enough water has been consumed.

"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,” Farrell said. "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.”

Farrell used functional magnetic resonance imaging (fMRI) to measure activity in parts of the brain associated with swallowing. He found that the right prefrontal areas were more active when participants were forcing themselves to swallow, suggesting that this part of the brain steps in to inhibit swallowing.

Drinking too much water makes humans susceptible to water intoxication and hyponatremia, a condition in which levels of sodium in the blood become too low. It can cause lethargy, nausea, convulsions and even comas.

"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," Farrell said.