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This article is part of our series about hydration.

How much water do we really need? How does hydration actually work? And what are the specific health benefits associated with maintaining proper hydration? As we embrace the summer season and brace ourselves for the soaring temperatures, it’s crucial to prioritize our well-being by taking necessary precautions.

Stay tuned to discover the correlation between hydration and mental health.


Maintaining adequate levels of fluid intake is critical for important physiological functions. In addition to the long-known negative effects of reduced fluid intake on physical performance, there is now growing evidence that acute dehydration can also impair cognitive function (1). These effects can result in work accidents and may particularly impact vulnerable populations such as children and adolescents whose brains are still developing, and elderly individuals who may have difficulty regulating appropriate fluid levels. As a result, there has been significant scientific and public attention focused on recommended daily water intake, with ongoing debates on appropriate policies in workplaces and schools.

We wanted to share two studies exploring the impact of dehydration on cognitive performance (1) and mood (2).

Scientists have reported that dehydration affects brain structure and function in healthy adolescents  (1). They used functional magnetic resonance imaging (fMRI) in 10 healthy adolescents (average age 16.8, with five females). Each participant underwent two conditions: a thermal exercise protocol and a nonthermal exercise control condition. The thermal exercise protocol participants were required to wear three layers of clothing which promoted more sweating and more weight loss compared to the control condition.

The study found that dehydration led to a significantly stronger increase in fronto-parietal blood-oxygen-level-dependent (BOLD) response during an executive function task compared to the control condition, which may negatively affect planning and visuo-spatial processing. BOLD response is a measure of brain activity that reflects changes in blood flow and oxygenation levels in response to neural activity. Given there was no change in cognitive performance after dehydration suggests an inefficient use of brain metabolic activity following dehydration. The study found that during an executive function task, dehydrated participants showed increased neuronal activity in order to achieve the same level of performance as when hydrated. This suggests that a prolonged state of reduced water intake can have a negative impact on executive functions such as planning and visuo-spatial processing. As brain metabolic resources are limited, the study suggests that proper hydration is important to maintain brain function.


By now we all know that staying hydrated is good for our bodies. But did you know that even mild hydration can affect mood?


A study investigated the effects of mild dehydration on cognitive function, and mood in healthy young women (2). The results showed that the women who were mildly dehydrated had worse mood, more difficulty concentrating, and more headaches.

The study involved 25 female participants with an average age of 23 years (2). They took part in three different 8-hour experiments, each with a different level of hydration: exercise-induced dehydration with no diuretic (DN), exercise-induced dehydration with a diuretic (DD), and optimal hydration (EU). The 3 experiments were conducted ~28 d apart during the 7-d placebo phase of each woman’s oral contraceptive schedule to control for their menstrual cycle (2).

The researchers evaluated their cognitive performance, mood, and dehydration symptoms during each experiment, both at rest and during three exercise sessions (2). For the DN and DD trials, the participants who experienced at least a 1% level of dehydrationere compared to their equivalent EU trials. The average dehydration achieved during the DN and DD trials was 1.36% of their body mass. The study found that dehydration caused negative effects on mood, with participants reporting feeling tired, fatigued, and having difficulty concentrating or performing tasks (2). Headache symptoms were also reported. However, most aspects of cognitive performance were not affected by dehydration. The study also found that the marker of hydration, serum osmolality, was greater in dehydrated trials compared to trials where participants were properly hydrated.

It’s not clear what exactly causes the negative mood changes that occur during dehydration. One possibility is that certain neurons in the brain detect dehydration and send signals to other parts of the brain that control mood, leading to negative feelings and other symptoms. It’s possible that these negative symptoms are a warning signal that humans have evolved to alert them before more serious consequences of dehydration occur, such as impaired performance that could affect survival.

In conclusion, the study found that mild dehydration (1.36% of body mass) had negative effects on mood, and ability to concentrate, and caused headaches in women (2). They also perceived tasks to be more difficult.Overall, the study suggests that there should be an increased emphasis on optimal hydration, especially during and after moderate exercise, to prevent negative effects on mood and cognitive function.


Interested to learn more about hydration? Explore our other articles.

Introduction to hydration article

The benefits of hydration

Hydration and heart failure


Silviya Demerzhan, Ph.D.

Chief Scientific Officer, Nordic Executive Medicine
Medical review by: Dr. Mahir Vazda MD


  1. Kempton MJ, Ettinger U, Foster R, Williams SCR, Calvert GA, Hampshire A, et al. Dehydration affects brain structure and function in healthy adolescents. Hum Brain Mapp. 2010 Dec 14;32(1):71–9.
  2. Armstrong LE, Ganio MS, Casa DJ, Lee EC, McDermott BP, Klau JF, et al. Mild Dehydration Affects Mood in Healthy Young Women1,2. J Nutr. 2012 Feb 1;142(2):382–8.