Hydration and cognitive performance

Since childhood, we have been taught that humans are mostly composed of water. And it absolutely makes sense since it is estimated that this substance makes up roughly 60% of our organism. Within these water management systems of the human body, the brain ranks first: supplying only 1/50th of body weight, it receives 18 to 20 percent of circulating blood. The water balance in the body has its own warning systems, so in situations when any organ needs an increased supply of fluid due to intense stress, the organism will alert us.

Water the brain as you do with flowers

Considering that the brain is mostly made up of water, it seems to be logical that the body’s water balance has an impact on brain structure. Daniel-Paolo Streitbürger and his associates in their study examined changes in brain structure, specifically those in white matter, gray matter, and cerebrospinal fluid during states of normal hydration, hyperhydration, and dehydration. Interestingly enough, a significant decrease in gray matter and white matter volume associated with dehydration was found in various brain regions. Most likely, this state of affairs shows some parallels between degenerative processes and the decline in cognitive abilities since a decrease in the volume of white and gray matter is also observed with the development of Alzheimer’s disease, expressed in the deterioration of intellectual performance.

Dehydration vs cognitive function

The human being is a unique creature, made up of many interdependent organs with multiple processes occurring simultaneously. The factors affecting the influence of dehydration on brain functioning are complex and have an indirect character. There are many theories that explain the negative impact related to the lack of water. Under the influence of dehydration, the body’s plasma volume is reduced, which can restrict blood flow to the brain and contribute to cognitive dysfunction. Dehydration also improves the concentration of cortisol, whose elevated levels may increase the brain’s vulnerability to the development of issues with proper cognition. Though the specific mechanisms regarding the impact of dehydration are not fully understood, researchers share the claim that dehydration of more than 2% of total body weight has a negative impact on cognitive functioning.

Cognitive performance is determined by a person’s ability to use mental resources. The list of mental functions includes perception, attention, memory, thinking, language, and other complex intellectual processes. Evidence suggests the tasks that require attention, immediate memory, and psycho-motor skills, as well as assessment of the subjective state, are the most negatively affected by dehydration. In contrast, based on the study of Ana Adan, working memory, long-term memory, and executive function skills seem to be more preserved, especially if the method used to induce dehydration is moderate physical exercise.

Fatigue and headache? Not a good match!

Although studies have not always shown a direct negative effect of dehydration on cognitive performance, some researchers concluded that dehydration may cause changes in subjective assessments, such as the feeling of being more tired as well as higher levels of perceived effort and concentration. The increase in fatigue is overcome by a more pronounced fronto-parietal brain activation, which may be experienced by participants as elevated effort. To put it simply – people affected by dehydration in order to perform a task with the same effectiveness as those who are appropriately hydrated, need more cognitive resources, which means they have reduced efficiency of cognitive processes.

It’s highly possible that we all have experienced a nagging headache in our lives, and it can be especially unpleasant in situations where we need a high concentration level, e.g. at work or during a college assignment. While dealing with the things that are important to us, we are at some risk of forgetting about the need to hydrate ourselves. In this aspect, it is necessary to point out the link between dehydration and headache or migraine. In the findings of Faezh Khorsha and his associates’ study from 2020, which involved 256 women, the researchers reinforced the opinion that drinking an adequate amount of fluids daily can contribute to the reduction of severity, duration, and frequency of migraine attacks as well as lower attack-associated impairment compared to those who drank less.

Stay balanced, though!

In contrast, intake of fluids above the norm also does not carry benefits. It’s actually the opposite as going beyond the threshold of how much water our body tolerates, can be particularly harmful. The danger, above all, comes from the risk of inflammation which is caused by high fluid intake in the body, along with low sodium levels. Infiltrating the cells with liquid substances affects their structure and overall metabolic processes. In more extreme cases, an excess of water in the body can contribute to the development of hyponatremia – a condition where the amount of sodium drastically decreases. The reason for this state is a hypothalamic-kidney feedback loop that is overwhelmed by increased fluid intake. Such sodium imbalances are claimed to be associated with cognitive impairment too.

So, what’s the best drink?

Speaking of the effect of hydration on human cognition, it is worth mentioning the types of beverages we consume. In one of the studies, a scientific team attempted to evaluate fluid intake and hydration status in association with cognitive functions in the group of 230 adolescents (10–14 years old). Among the daily fluid types, intakes of soft drinks, sweetened tea and total sugar-sweetened beverages were negatively correlated with cognitive function. So, what does it mean, really? Although we shouldn’t draw any strong conclusions, it’s possible that interventions aimed at decreasing the consumption of sugar-sweetened beverages and increasing hydration status through healthy drink choices, such as water, could improve cognitive performance in adolescents. It is worth noting that drinks containing high amounts of alcohol, caffeine, and sugar are most likely to perform as diuretics in the body and promote dehydration.

Final note

To summarize the matters mentioned above, dehydration can affect brain structure and functioning. After all, the human brain is composed mostly of water and even mild dehydration can cause changes in brain volume, leading to impaired cognitive processes such as reduced attention, memory, or executive function. Severe dehydration can cause headaches, confusion, and in the more extreme cases even unconsciousness. Additionally, a lack of water can also lead to changes in blood volume and circulation, which may affect the delivery of oxygen and nutrients to the brain increasing the risk of dizziness or fatigue. As obvious as it may sound, it is important to maintain proper hydration levels to support optimal brain function. Now, let’s all raise a glass of water!

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