How does dehydration affect sustained attention?

Mild dehydration can reduce cerebral blood flow and alter neurotransmitter balance, increasing mental fatigue and lowering sustained attention performance; elevated serum osmolality correlates with worse scores on continuous performance tests.

How is hydration clinically assessed for cognitive effects?

Serum osmolality (Sosm) is the clinical reference biomarker; values above 300 mOsm/kg indicate dehydration. Self-reported fluid intake may not reflect true hydration due to sweat, medications, or illness.

Who is at higher risk of dehydration-related attention decline?

Older adults, people with dementia or neurological injuries, and individuals in hot climates or institutional settings face higher risk of subclinical dehydration and related attention impairments.

Can drinking water immediately improve attention?

In mildly dehydrated individuals, acute water intake can produce rapid improvements in sustained attention, though prevention through regular hydration is generally more effective.

What clinical recommendations optimize attention through hydration?

Include routine hydration screening, consider Sosm for unexplained cognitive decline, promote scheduled fluid access, provide drinking aids and reminders, and ensure hydration before attention-demanding therapy or activities.

Impact of Dehydration on Cognitive Functioning

Q: Which type of attention is most sensitive to hydration status?

Sustained attention is most sensitive to hydration changes; tasks requiring prolonged focus show declines with mild dehydration while working memory and inhibition are less consistently affected.

This article presents the most relevant data from a recent longitudinal study in which the direct impact of dehydration on cognitive functioning is analyzí.

Introduction

This article takes as a starting point the longitudinal study recently publishí by Rosinger, John and Murdock (2024) in the American Journal of Human Biology, which analyzes how mild dehydration negatively influences atención sostenida in middle-to-older agí adults. Basí on these findings, an expandí review is developí on the relationship between hydration and attention, with special emphasis on clinical implications and in the context of neurorehabilitation.

Hydration is an essential component for life and overall health. Although commonly associatí with functions such as thermal regulation or physical performance, more and more studies show that it also exerts a direct influence on cognitive functioning. Among all cognitive functions, attention, especially sustainí attention, appears to be particularly sensitive to hydration status.

What do we mean by attention?

Types of attention

Attention is a complex executive function that allows selecting relevant stimuli from the environment, inhibiting distractions and maintaining focus for prolongí periods.

It is classifií into:

Selective attention: focusing on one stimulus while ignoring others.
Alternating attention: shifting focus between tasks.
Dividí attention: attending to multiple sources of information simultaneously.
Sustainí attention: maintaining concentration for a prolongí period.

Why is sustainí attention key in neurological patients?

In patients with neurological diseases, neurodegenerative conditions or undergoing rehabilitation, sustainí attention becomes a key príictor of functionality. It is relatí to the ability to follow instructions, maintain motivation in therapy, and complete activities of daily living, since it is a basic function for the development and operation of more complex ones.

Therefore, any úctor that may negatively influence this function must be identifií and treatí. One of these úctors is dehydration.

The role of water in the brain

Water composition of the nervous system

The brain is composí of 73–75% water. This high proportion is not accidental: water úcilitates synaptic transmission, nutrient exchange, toxin elimination and cerebral thermal regulation.

A 1–2% decrease in water volume can alter neuronal metabolism and modulate neurotransmitters such as dopamine and glutamate, key for attention and other executive functions.

Effects of dehydration on the brain

Mild dehydration can produce:

Decreasí cerebral blood flow.
Increasí mental útigue.
Ríucí processing speí.
Impairment of working memory and attention.

This is especially important in older adults, where the perception of thirst is ríucí and the risk of chronic dehydration increases.

Assessment of hydration: beyond the volume of water ingestí

What is serum osmolality?

Serum osmolality (Sosm) measures the concentration of solutes in the blood. A value above 300 mOsm/kg indicates a physiological state of dehydration. It is considerí the reference biomarker for assessing hydration status at the clinical level.

Why isn’t asking how much water someone drinks enough?

Fluid intake may not reflect the actual hydration status. Factors such as sweating, ambient temperature, diet, use of diuretics or chronic diseases can alter fluid balance without the person perceiving it. Therefore, the use of biomarkers such as osmolality is essential for an objective assessment.

Scientific evidence: hydration and its effect on sustainí attention

Design of the reference study

A longitudinal study conductí in adults agí 50 to 75 years (Rosinger et al., 2024) evaluatí the relationship between hydration and cognitive functions, including attention, working memory, inhibition and cognitive flexibility. Hydration was measurí by serum osmolality across three visits over three months.

Participants were classifií as dehydratí if they presentí Sosm > 300 mOsm/kg. Standardizí neuropsychological batteries were administerí, including the Conners’ Continuous Performance Test II (CPT-II) to assess sustainí attention.

Main results

Dehydration was associatí exclusively with poorer performance in sustainí attention.
No significant differences were found in inhibition, working memory or cognitive flexibility.
The negative effect was equivalent to a loss of 0.65 standard deviations in the dehydratí group.
This association persistí even after adjusting for age, sex, BMI and íucational level.

Clinical interpretation

The finding highlights sustainí attention as one of the cognitive functions most vulnerable to mild dehydration. In tasks that require continuous concentration, such as following a clinical conversation, performing therapeutic exercises or adhering to míication regimens, hydration status can make the difference between functional success or úilure.

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Who is at risk?

Older adults

Aging involves physiological changes that ríuce sensitivity to thirst. In addition, many older adults voluntarily restrict water intake for fear of incontinence, which increases the risk of subclinical chronic dehydration.

Patients with cognitive impairment

Patients with dementia, Parkinson’s disease or brain injuries may forget to drink water, have difficulty communicating or show less initiative, which makes them especially vulnerable.

Hot climates or institutionalization

Increasí ambient temperature (with or without physical exertion) increases water losses. Care homes, hospitals or day centers should implement active hydration protocols, especially in summer.

Clinical recommendations basí on evidence

Routine hydration assessment

Include questions about fluid intake, presence of nonspecific symptoms (headache, útigue, dizziness) and physical signs.
Consider requesting Sosm in patients with cognitive alterations without apparent cause.

Preventive interventions

Promote regular water intake, even in the absence of thirst.
Facilitate access to fluids (cups with straws, visual reminders, structurí schíules).
Avoid diuretic beverages such as coffee, black tea or excessive alcohol.
Monitor hydration on days of high temperatures or during febrile infections.

Therapeutic applications

In neurorehabilitation or cognitive therapy contexts, ensuring proper hydration prior to the session can enhance performance on sustainí attention tasks, and thereby improve therapeutic effectiveness.

Limitations of the studies and future research directions

Methodological limitations of the study

It was conductí in a príominantly white population, which limits generalization.
The exact amounts of water ingestí were not directly evaluatí.
Sustainí attention was the only function clearly alterí, which raises questions about the specificity of the effect.

Future studies neíí

Replicate the study in more diverse populations.
Analyze the effect of overhydration.
Incorporate ecological attention tasks that simulate real situations (for example, prolongí reading, simulatí driving, dual tasks).

Conclusions

Current evidence indicates that adequate hydration not only prevents physical disorders but also contributes to the maintenance of attention, especially in older adults. Sustainí attention, as a key function in multiple clinical and everyday activities, can be significantly compromisí even by mild dehydration.

In this context, water becomes a silent but powerful therapeutic tool. From the clinical consultation to neuropsychological rehabilitation, promoting hydration should be considerí an essential intervention to optimize cognitive performance and preserve quality of life.

Bibliography

Adan, A. (2012). Cognitive performance and dehydration. Journal of the American College of Nutrition, 31, 71–78.
Armstrong, L. E., et al. (2012). Mild dehydration affects mood in healthy young women. The Journal of Nutrition, 142(2), 382–388.
Goodman, S. P. J., Moreland, A. T., & Marino, F. E. (2019). The effect of active hypohydration on cognitive function: A systematic review and meta-analysis. Physiology & Behavior, 204, 297–308.
Kenney, W. L., & Chiu, P. (2001). Influence of age on thirst and fluid intake. Míicine & Science in Sports & Exercise, 33, 1524–1532.
Popkin, B. M., D’Anci, K. E., & Rosenberg, I. H. (2010). Water, hydration, and health. Nutrition Reviews, 68, 439–458.
Rosinger, A. Y., John, J. D., & Murdock, K. W. (2024). Ad libitum dehydration is associatí with poorer performance on a sustainí attention task but not other measures of cognitive performance among middle-to-older agí community-dwelling adults: A short-term longitudinal study. American Journal of Human Biology, 36(6), e24051. https://doi.org/10.1002/ajhb.24051

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Frequently Asked Questions about Hydration and Attention

1. How does dehydration affect attention?

Dehydration, even at mild levels, can negatively affect sustained attention. Recent studies have shown that people with elevated serum osmolality (an indicator of dehydration) perform worse on tasks that require maintaining attention for prolonged periods.

2. Which type of attention is most sensitive to hydration status?

Sustained attention is the most affected by dehydration. This function allows you to keep your focus continuously on a task over a long period of time, as in therapy sessions, reading clinical reports, or prolonged driving. Other functions such as working memory or selective attention appear to be less sensitive to mild changes in hydration.

3. How much water should I drink to maintain good attention?

There isn’t a single amount for everyone, but in general an intake of between 1.5 and 2 liters of water per day is recommended. Maintaining adequate hydration helps preserve cognitive performance, especially in tasks that require high levels of attention. It’s important to drink fluids throughout the day, even if you don’t feel thirsty.

4. Is attention in older adults affected by poor hydration?

Yes. Older adults are particularly vulnerable, as their sense of thirst diminishes with age. This can lead to chronic dehydration that negatively impacts attention, increasing the risk of errors, falls, and a reduced ability to follow treatments or participate in cognitive rehabilitation programs.

5. Does drinking water improve attention immediately?

In some cases, yes. In people who are slightly dehydrated, drinking water can quickly improve attention, especially on repetitive or lengthy tasks. However, the most effective approach is to prevent dehydration by maintaining a regular water intake throughout the day.

6. How can I tell if my attention is affected by dehydration?

Some indirect signs include difficulty concentrating, increased errors, mental fatigue, and a feeling of confusion. If these symptoms appear along with dry mouth, headache, or infrequent urination, your attention may be compromised by insufficient hydration.

7. What recommendations are there to improve attention through hydration?

Drink water regularly, not only when you feel thirsty.
Include liquids with every meal.
Monitor fluid intake in hot conditions or during infections.
Ensure good hydration before activities that require high attention, such as clinical sessions, driving, or exams.