Does Mild Dehydration Affect Brain Function? Explained

Last Tuesday we had a games period before mathematics, which is already a dangerous combination for me. We played football outside and it was very hot. I had forgotten my water bottle at home, but I did not tell anybody because I thought one school day without it would be fine.

After games, our maths teacher gave us a small test. I knew how to solve the first question because I had practised it the night before. But I read it again and again and the numbers were just not staying inside my head. I also had a little headache and everybody was irritating me, even though they were not really doing anything.

My teacher saw that my bottle was missing and asked how much water I had drank. That made me wonder about dehydration and brain function. I always thought dehydration was something that only happened to people lost in a desert. I did not know it could start in a normal classroom.

What does mild dehydration mean?

Dehydration means the body is losing more fluid than it is receiving. We lose water when we sweat, breathe, go to the toilet or become sick. If we do not replace it, the body slowly starts running short.

The word “mild” confused me. How can dehydration be mild? My mother explained that it means the body has lost some water, but the person is not dangerously ill. They may still walk, talk and do their work. They might just feel thirsty, tired, dizzy or have a dry mouth.

The Mayo Clinic says dehydration happens when the body uses or loses more fluid than it takes in. It also says mild or moderate dehydration can usually improve by replacing fluids, while severe dehydration needs medical treatment. So there is a big difference between forgetting water during games and becoming seriously dehydrated.

Why would the brain even notice?

I thought water was mostly for sweat and thirst. But our brain also needs the body to have the right balance of water and minerals. Water helps the blood carry oxygen and nutrients, and it helps the body control its temperature.

When the body starts losing water, it has to make small adjustments to keep everything working. Feeling thirsty, tired or uncomfortable may also make a difficult task feel even more difficult. My maths question did not actually become harder, but it definitely felt harder to me.

I searched “dehydration cognitive effects” online, but most explanations used very big words. What I understood was that scientists test different parts of thinking, such as attention, reaction time, working memory and the ability to stay alert. These are not all the same thing. Dehydration might affect one type of task but not another, which is why the answer is not so simple.

What did the scientists find?

In 2012, researchers published a study called “Mild Dehydration Affects Mood in Healthy Young Women” in The Journal of Nutrition. It involved 25 healthy young women who completed different tests while hydrated and mildly dehydrated.

The average water loss in the dehydrated condition was about 1.36 percent of body mass. That number looked very small to me. But the women reported more headaches, tiredness, difficulty concentrating and a feeling that tasks were harder. Still, most of their measured thinking performance did not become worse.

I had to read that part two times. The women felt worse and found the tasks harder, but many of their actual test results did not change much. So feeling mentally foggy and performing badly are connected, but they are not always exactly the same.

Another study published in the British Journal of Nutrition in 2011 tested 26 healthy young men. Their average dehydration was about 1.59 percent of body mass. Researchers found changes in vigilance and working memory, along with more fatigue and tension.

But both studies was small and involved young adults, not ten-year-old children sitting in a maths class. Exercise and a medicine that increases urine were also used during parts of the experiments. This means the results are interesting, but they cannot decide what happens to every person in every normal situation.

Why the answer is still a bit messy

I thought science would give one neat answer. Drink less water, brain works badly. Drink more water, brain works perfectly. But it does not work so nicely.

A 2015 review in Nutrition Reviews looked at hydration, mood and mental performance. It said mood, fatigue and alertness are more consistently affected when dehydration causes a loss of more than 2 percent of body mass. But the effects on thinking were less consistent. The review also said more research was needed for smaller water losses that happen in ordinary life.

When I searched “dehydration focus concentration,” some pages made it sound like one missed glass of water will switch off the brain. That is not what the studies say. Mild dehydration may affect how a person feels and may affect certain thinking tasks, but the size of the effect can change between people and situations.

Was my bad maths test really because of water?

I cannot prove that. Maybe I was tired from football. Maybe I was worried about the test. I also slept late the previous night because I was watching cartoons when I was not supposed to.

Hunger, heat, poor sleep, stress and illness can all make concentration more difficult. So I can simply not understand the maths chapter properly, which is probably also part of my problem.

The words “mild dehydration symptoms brain” appeared when I searched, but that phrase made dehydration sound like a brain disease. A headache or one forgetful afternoon does not automatically mean something is wrong with the brain. Hydration and memory may be connected in some situations, but water cannot replace sleep, food, practice or medical care.

And drinking one glass does not turn someone into a genius. I drank water after my teacher noticed, but I still got one answer wrong.

Small signs I started noticing

Now I notice when my mouth feels dry, my urine looks darker, or I have not gone to the toilet for a long time. I also notice thirst, tiredness, dizziness and headaches. These can happen with dehydration, but they can happen for other reasons too.

My mother told me not to wait until I feel horrible. I take my bottle to school and sip after games instead of drinking a lot at once. Our teacher also lets us keep bottles near our desks, as long as nobody turns them into water guns.

But confusion, fainting, unusual sleepiness, very little urine or a fast heartbeat should not be treated like a small classroom problem. A parent, teacher or doctor needs to help. Medline Plus explains that severe dehydration may require urgent medical treatment.

Also, some people with heart or kidney conditions may receive special instructions about fluids. They should follow their doctor, not a ten-year-old with a blue water bottle.

Learn more about how the extra hydrogen water helps our body to be fit and more active!

What I understand now

Mild dehydration does not make the brain stop working. But it may make some people feel tired, irritated or less able to concentrate, specially during heat or exercise. Research also shows that the effect is not identical for everybody.

I still forget my bottle sometimes. Yesterday I remembered the bottle but forgot my maths notebook, so clearly water has not fixed everything.

But now, before games period, I take a few sips and check that the bottle is full. It is a very small habit and it cannot promise perfect marks. At least next time a maths question disappears from my head, I will have one less reason to wonder why.

Sources

Author bio: Written by a curious ten-year-old who likes asking “why” about everyday things like water, sleep and food. This article was shared with support from the team at Dvine H2O, who care about clean and safe drinking water for families.