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Why is being hydrated actually so important..?

You've definitely heard about how you should always be well hydrated, but why exactly is that?

Well, water makes up for around 50-70% of the human body weight and is essential for the body to work properly. It helps with metabolism, keeps electrolytes balanced, transports nutrients, lubricates joints and organs, and gives structure to cells and tissues.

When your body lacks enough water (dehydration), it can cause serious issues and impair brain function. Many studies show the importance of staying hydrated to maintain or even improve cognitive function.

Effects of Dehydration

The body typically loses about 2550ml of water daily, including 300ml through breathing, 450ml through sweat, 1600ml through urine, and 200ml through feces. 

Exercise, humidity, heat, and health conditions can increase water loss to over 3100ml/day, so it's crucial to replenish fluids by drinking about 2 litres (8 cups) of water, along with other beverages and food.

When water loss exceeds intake, blood volume drops, leading to low blood pressure and increased plasma osmolarity. This triggers mechanisms like decreased urine output and increased thirst. 

Effects of Dehydration on Cognitive Function 

The brain, consisting of 75% water, relies on hydration for metabolic support, structural integrity, and nutrient transport, crucial for proper brain function.

Studies have shown that even mild dehydration, around 2% loss of body water, can impair cognitive function. This can manifest as difficulties in concentration, slower reaction times, memory issues, and mood changes. Such water loss can occur during routine daily activities, especially in adults who drink only about 1 litre (or 4 cups) of water a day.

Physiological symptoms of mild dehydration affecting the brain include light-headedness, dizziness, headaches, nausea, and fatigue. 

Daily headaches may often be attributed to mild dehydration, further contributing to cognitive decline.

In a study involving young adults, mild dehydration significantly impacted women's cognitive function, causing fatigue, headaches, and concentration difficulties, while men were less affected. Another study found similar effects during 24-hour water fasting, including increased sleepiness, fatigue, and worsened moods.

Rehydration improved mood but did not fully reverse fatigue, suggesting that prolonged dehydration can have lasting effects on the brain despite re-hydration

Effects of Hydration on Brain Function

In another study, habitual high-volume drinkers reduced their water intake to 1 litre per day, while low-volume drinkers increased theirs to 2.5 litres per day for 3 days. 

Results showed that increased water intake led to better mood, reduced sleepiness, and less thirst, while decreased intake resulted in worsened mood and increased thirst.

Increasing daily water intake, even by a few extra glasses, can have lasting positive effects on mood, energy, and cognition.

Whereas consistently drinking less than 1.2 liters per day and being dehydrated impairs cognitive function and daily functioning.

This is especially important for the elderly, who are more susceptible to cognitive decline when dehydrated. Similarly, well-hydrated younger children perform better academically and behaviorally.

This is why regular hydration, particularly around 2 litres per day or more for adults, supports cognitive functioning, while dehydration can negatively impact mood and memory.


Staying well-hydrated is crucial for cognitive function. 

Water, making up 50-70% of body weight, is essential for metabolism, nutrient transport, and brain function. Dehydration, even mild, can impair cognitive abilities, manifesting as concentration difficulties, slower reaction times, and mood changes. Rehydration is key to reversing these effects.

Ensuring regular hydration, especially around 2 litres per day, supports optimal cognitive functioning, while dehydration leads to fatigue, mood changes, and decreased attention.

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