We all know that drinking water regularly is good for the body. But new research has revealed that drinking water when we feel thirsty boosts our brain’s performance in mental tests.

Researchers from the University of East London and the University of Westminster in the UK analyzed the potential effects of water on cognitive performance and mood among 34 participants with an average age of 29 years.

The study, published in the journal Frontiers in Human Neuroscience, involved participants taking part in a “water” and a “no water” experiment one week apart.

The “water” experiment required the people to complete a number of mental tests after eating a cereal bar and drinking some water. The “no water” test meant the participants consumed just the cereal bar alone. The amount of water drunk by the participants in the “water” test depended on their level of thirst.

Lead study author, Dr. Caroline Edmonds of the University of East London School of Psychology, told Medical News Today, “Our study found that reaction times were faster after people drank water, particularly if they were thirsty before drinking.”

In both experiments, the participants were asked to fast overnight, consuming no food or drink after 9pm before the day of testing. The participants were assessed via three measurements – a thirst scale, a mood scale and with a computer-administered variety of tasks called the Cambridge Neuropsychological Test Automated Battery (CANTAB).

The researchers analyzed particular areas of the participants’ brain, including reaction time, verbal recognition memory, visual memory and learning.

The participants who drank around three cups of water (775 milliliters) just before completing the tests had a 14% increased reaction time compared with those who did not drink any water.

The study authors say that as well as showing that water consumption can increase cognitive performance, this is moderated by the participants’ subjective feelings of thirst. The authors say:

The present study revealed water consumption to have contrasting effects on different cognitive processes. Water consumption was found both to impair ‘set shifting’ performance, and to facilitate speed of responding, but in a manner that was dependent upon subjective thirst.

More specifically, water consumption appeared to have a corrective effect on the response times for thirsty individuals, bringing their speed of responding up to the level of non-thirsty individuals”

In terms of mood, the results revealed that when participants were dehydrated, they were more tense, sad and confused.

But the study also showed that drinking water can have negative effects on cognitive performance. Dr. Edmonds told MNT the study “also showed that people performed worse on a complex rule-learning task after drinking.”

In a test called the Intra-Extra Dimensional Set Shift (IED) test, the participants were monitored for “attention flexibility” and tested on their error rates in discriminating a series of visual images. Depending on how the researchers ran the test, participants who drank water before doing it performed worse than those who drank no water.

The study authors add that further research is needed to examine how the brain effects of water are mediated by thirst mechanisms, as well as determining why water consumption can also have negative effects on cognitive performance.

Dr. Edmonds told MNT: “This study shows that water can be helpful for cognitive performance, and sometimes it can be helpful to be thirsty – we need to do more studies to find out why.”

So is there an ideal amount of water that we should be drinking for strong mental performance? Dr Edmonds told us there is no simple answer:

We don’t really know the answer to that question at the moment.

This study is part of a program of research that is investigating how much water we should consume to affect cognitive performance.

[There is also] a whole host of other research questions, such as what cognitive tasks are affected, and how far in advance of performance on these tasks is optimal for improving performance.”