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  • Brian Bender, PhD

Dehydration and Cognitive Performance: How to Stay Focused

Updated: Jan 12, 2022

A feeling of brain fog is all too common for most of us. But an important part of your diet may be contributing to a lack of cognitive function and cognitive performance: hydration.

Role of Hydration in Cognitive Performance

Maintain focus and cognitive function with proper hydration.

As we age, there are some declines in mental performance that are to be expected. Some normal age-related changes include decline in tasks that involve attention-switching (multitasking), slower response times, and reduced speed of information processing.

There are many causes for this decline in cognitive performance. And for many, knowing these causes can help you make changes to slow or stop its progression.

For example, it is well known that physical exercise can help mediate declines in cognitive performance as we age. Physical exercise helps re-grow and re-arrange neurons in the brain and directly enhance cognitive performance. In fact, even 10 minutes of daily walking can improve outcomes.

Another well-known cause of mental decline is due to sleep deprivation. Both temporary and chronic sleep deprivation can impair brain function and lead to worsening cognitive performance.

However, it is becoming evident that another often overlooked cause of both temporary and chronic decline in mental clarity and cognition is proper hydration.

Previously, a loss of at least 2% of your body weight in water was enough to cause a negative effect on cognitive performance. However, newer research continues to show this mental decline can happen sooner.

Studies in both women and men show effects occurring between 1 and 2 % loss in weight due to water depletion. To put this into perspective, a 150 pound woman could begin to feel feelings of fatigue, anxiety, lower concentration, and degraded mood at as little as 1.5 to 3 pounds lost from dehydration.

And a randomized controlled trial published in the American Journal of Clinical Nutrition showed negative effects at less than a 1% loss, with evidence of a decline in subjective energy and increased anxiety and depression whereby the effects were reduced by drinking water.

All these studies appear to indicate that cognitive performance starts to become compromised even at mild levels of dehydration, effecting such things as mood, working memory, and concentration.

This is a challenge for athletes during training and during competition. In addition to operating at peak physical performance, peak mental performance is critical for most sports that require focus and a rapid and dynamic assessment of strategy and execution.

This is also a challenge for employees and employers alike, where dehydration can effect workplace safety and productivity through cognitive impairment.

Monitoring Hydration Status

Using your own feelings of “thirst” is not a bad approach for indicating dehydration. However, thirst is very subjective and may only start to develop at different levels of dehydration in different individuals. And for many, thirst does not develop until over 1% of body water mass is lost. And we’ve just learned, this degree of dehydration may already be imposing negative cognitive effects.

Elite athletes have been tracking hydration for decades, and it has been know that urine parameters such as color, specific gravity, and volume are the most valid markers of hydration status in athletes and military personnel in situations of acute dehydration.

The role of the kidneys is to filter the blood, whereby water concentration helps flush out these various proteins and metabolites. When your total body water content is low (a state of dehydration), the concentration of these urinary constituents is high leading to a darker color and higher specific gravity. On the other hand, when your total body water content is high (a state of proper hydration), the concentration of these same urinary constituents is low, leading to a lighter color urine approaching that of water and a lower specific gravity (also approaching that of water).

NASM urine color assessment.

Recent studies have also pointed to these same markers as valid hydration markers in less active individuals, too.

For example, a study of twenty women at normal levels of activity also identified urine specific gravity as the best physiological measure of hydration status.

For those without the means to easily these urine parameters directly, urine color is another approximation. The darker the color, the more dehydration one tends to be.

Staying Hydrated Throughout the Day

To maintain proper hydration through the day to fend off any fatigue or lack of mental clarity caused by poor hydration, the simple advice is to keep sipping water. But the advice is often easier said than done.

Some people have a harder time drinking water than others due to taste. In that case, flavored waters are perfectly acceptable. However, it is advised to significantly limit sugar-based flavorings, because sugar-sweetened beverages are a major source of extra, nutrient-poor calories. A squeeze of a lemon is often a go-to practice for many nutritionists.

But it’s important to find a practice that works for you that you can work into your normal routine and maintain day after day. The long-term effects of dehydration are still not well understood, but hydration’s links to cardiovascular health have been a source of study and hypothesized to contribute to long-term chronic diseases.

If you consistently find yourself feeling thirsty from day to day, try to find ways to add more water to your diet. One technique can be as simple as carrying around a water bottle all day. As mentioned by the National Athletic Trainers’ Association, the simple act of having water handy leads to being more consistently hydrated.

It’s also important to remember to re-hydrate after exercise or competition. Hydration is a key element to a quick recovery, and dehydration can delay both physical and mental recovery. In fact, it is possible for dehydration-related effects on cognition and mood to persist at least a day after the end of intense physical activity leading to dehydration.

Hydrate for Happiness

Hydrate well for good mental health.

We’ve all probably heard that staying hydrated is important for good health, but it’s important to remember the link to mental clarity and cognitive performance. Part of this, however, includes mood.

Hydration’s link to mood is interestingly been studied as it relates to happiness.

In studies of children and a small group of women, dehydration was linked to lower ratings of happiness.

But not to worry. As the author’s note, “…deleterious effects of [fluid deprivation] on alertness, happiness and confusion were immediately reversed by drinking…”

So remember to keep your water glass full! For focus. For health. For peak performance. And for happiness!



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