Water. More than two thirds of your body is water. A source from the Journal of Biological Chemistry puts the percentage of water in the various parts of your body as follows:

  • brain and heart – 73%
  • the lungs – 83%
  • the skin – 64%
  • muscles and kidneys – 79%
  • Interestingly, even your bones are 31% water!

All this water in your body serves several important functions, including the regulation of internal body temperature, being a mode of transport for nutrients, flushing out toxins and waste, lubricating joints and forming saliva and keeping the skin healthy. Just think about dried out PlayDoh and you will get the picture!

Now consider your brain, the master that orchestrates everything else going on in your body. It is a soft, spongy organ that is literally floating in a watery, salty fluid enclosed by layers of membranes. This fluid is the CerebroSpinal Fluid (CSF) whose job is to support and cushion the brain and nourish it.

Your body constantly loses water through sweating, urinating and generally functioning as it should. You also constantly replenish the water by eating and drinking. When you lose more water than you take in, the normal water content in your body is reduced and this upsets the delicate balance of various minerals such as salts and sugar in your body. This is dehydration and it is bad news because this balance is essential for the body to function properly.

When the amount of water in and around the brain is reduced, your brain is dehydrated. It was recently observed that dehydration causes shrinkage of brain tissue and an associated increase in ventricular volume. This means that with dehydration, there is less brain and more space in your head!

Interestingly, research evidence for poor cognitive performance as a result of dehydration is limited. What we do know for certain is that the effects of dehydration on attention and memory are significant. Being dehydrated by just 2% impairs attention, psychomotor and immediate memory skills and awareness and assessment of your own subjective experience. This means that the dehydrated brain will be distractible, find it hard to focus, have poor eye-hand and motor coordination, not remember things in the short-term and be somewhat confused.

One study showed that while neuronal activity increased with dehydration, it was not associated with better cognitive performance. Simply put this means that the dehydrated brain has to work harder to achieve the same level of performance. This is metabolic inefficiency and over time, it will affect executive functions such as planning and visuo-spatial processing (for instance locating your car in the suffocatingly hot and huge mall carpark).

What Are Some Behaviours That Signal Dehydration?

Mild to moderate dehydration is characterized by thirst, restless or irritable behaviour. You might also see the following behavioural signs:

  • confusion
  • dizziness
  • lightheadedness
  • difficulty talking
  • blurred vision

Severe dehydration will lead to lethargy or unconsciousness, seizures and eventually death. Remember that by the time your brain is that dehydrated, you cannot spot the signs yourself!

But maybe you just want to stay focused and do your best on a test or in that interview. Do yourself and your brain a favour, and stay sensibly hydrated.

Shrimathi Swaminathan
Clinical Psychologist

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