16 August 2016 - The Conversation - Memory and attention are affected by much lower levels of dehydration than previously thought

We’re often told we should drink eight glasses of water a day, check that our urine is not too yellow, and limit caffeinated drinks because they make us lose hydration.
Such everyday advice implies that dehydration is a common problem, but the traditional view when it comes to the science is that this view is not supported by research. Rather it has been assumed that if your lifestyle does not include prolonged activity, or the temperature is not particularly high, most of the time the level of fluid in your body will be in the normal range.
However, our new research, published in The American Journal of Clinical Nutrition, is challenging this received wisdom. We found, for the first time, that the functioning of our brains can be compromised by just a minor degree of dehydration.
Previous studies have found when there is a water loss of around 2% of body weight then memory, attention and mood are adversely affected. This is typically associated with periods of extended physical activity – and much dehydration research has focused on this area, rather than the everyday water loss that we examined.
Water makes up nearly two-thirds of the body and is an essential nutrient, necessary for all aspects of bodily functioning including the distribution of oxygen and other nutrients, the removal of waste products and the regulation of temperature. Its importance is illustrated by a person dying within as little as three to five days if they do not drink. However, the body can be affected by dehydration well before the point of death.
It is well accepted that the performance of athletes will suffer if they lose too much fluid. During a single match, a footballer may run 12 or more kilometres and lose up to 3% of their body weight. If they initially weigh 75kg they will have lost 2.25kg – that is nearly five pounds of weight – which reflects a loss of half a gallon of water.