Your brain is strongly influenced by your hydration status.

Studies show that even mild dehydration, such as the loss of 1–3% of body weight, can impair many aspects of brain function.

In a study in young women, researchers found that fluid loss of 1.4% after exercise impaired both mood and concentration. It also increased the frequency of headaches.

Many members of this same research team conducted a similar study in young men. They found that fluid loss of 1.6% was detrimental to working memory and increased feelings of anxiety and fatigue.

A fluid loss of 1–3% equals about 1.5–4.5 pounds (0.5–2 kg) of body weight loss for a person weighing 150 pounds (68 kg). This can easily occur through normal daily activities, let alone during exercise or high heat.

Many other studies, with subjects ranging from children to older adults, have shown that mild dehydration can impair mood, memory, and brain performance.

Mild dehydration (fluid loss of 1–3%) can impair energy levels, impair mood, and lead to major reductions in memory and brain performance.