Many people claim that if you don’t stay hydrated throughout the day, your energy levels and brain function start to suffer.

And there are plenty of studies to support this.

One study in women showed that a fluid loss of 1.36% after exercise impaired mood and concentration and increased the frequency of headaches 

Other studies show that mild dehydration (1–3% of body weight) caused by exercise or heat can harm many other aspects of brain function

Keep in mind that just 1% of body weight is a fairly significant amount. This happens primarily when you’re sweating a lot.

Mild dehydration can also negatively affect physical performance, leading to reduced endurance 

SUMMARY

Mild dehydration caused by exercise or heat can have negative effects on both your physical and mental performance