Mild Dehydration Impairs Coginitive Functions

Mild Dehydration Impairs Coginitive Functions
February 22, 2012 No Comments » Healthy Lifestyle Brian Fulton

Two recent studies have found that mild dehydration can alter a person’s mood, energy level, and ability to think clearly. Mild dehydration appears to affect people in the same manner whether they are exerting themselves or are sitting at rest. One study looked at twenty-five women aged 23 on average and was published in The December 2011 edition of the Journal of Nutrition. The other was performed on twenty-six men with an average age of 20 and was published was published in the November 2011 British Journal of Nutrition. Both studies were performed at the University of Connecticut’s Human Performance Laboratory. All of the participants were healthy, active individuals, who were neither high-performance athletes nor sedentary – typically exercising for 30 to 60 minutes per day.

Subjects were put through a battery of cognitive tests that measured vigilance, concentration, reaction time, learning, memory, and reasoning. They were tested when completely hydrated, then tested again after exercise-induced dehydration. Each participant took part in three evaluations that were separated by 28 days.

The female study noted headaches, fatigue, and difficulty concentrating from mild dehydration caused . Subjects also perceived tasks as more difficult when slightly dehydrated, but there was no substantive reduction in their cognitive abilities.

The other study, which looked and males showed that mild dehydration caused some difficulty with mental tasks, particularly in the areas of vigilance and working memory. While subjects in this group also experienced fatigue, tension, and anxiety when mildly dehydrated, adverse changes in mood and symptoms were “substantially greater in females than in males, both at rest and during exercise,” according to the study.

Why the human body is so adversely affected by mild dehydration is not entirely understood, but research has shown that neurons in the brain detect dehydration and may signal other parts of the brain, regulating mood when dehydration occurs. Mild dehydration is defined as an approximately 1.5 percent loss in normal water volume in the body. This sounds like an extremely small number, so why is it that we seem to be affected by such a minimal amount of water loss? One of the studies’ lead scientists is Lawrence E. Armstrong, a professor of physiology in University of Connecticut’s Department of Kinesiology in the Neag School of Education. Armstrong says that, “Our thirst sensation doesn’t really appear until we are 1 percent or 2 percent dehydrated. By then dehydration is already setting in and starting to impact how our mind and body perform.”

What we do know is that our brains have a much higher percentage of water than our bodies do, and as a result are much more sensitive to dehydration. This would make sense. Our brains are much more sensitive to many things that our bodies can tolerate (for example oxygen deprivation). I actually found it difficult to get definitive information on the percentage of water in our bodies and our brains. Different sources quote different numbers. The University of McGill information indicates the brain contains 95% water. The US Geological Survey’s Science for Schools site puts it at 70%.  What is clear is that our brains appear to have up to 20% more water than in our body in general with our brain actually floating in water (cerebrospinal fluid). This is why hydration is so important.

So, how do we stay hydrated? There is no shortage of information on this topic, and most of it is quite dependable. In order to stay properly hydrated, experts like Armstrong recommend that individuals drink eight, 8-ounce glasses of water a day, which is approximately equivalent to about 2 litres of water. As a rule, no matter what age you are or what health you are in, a good rule of thumb is that if you are not peeing at least four to five times per day then you are not properly hydrated. Urine should be very pale yellow in colour. Urine that is dark yellow or tan in colour indicates greater dehydration. As you might expect, proper hydration is particularly important for high-risk groups, such as the elderly, people with diabetes, and children.

Is it possible to drink too much water? The answer is “rarely”. This can occasionally happen in individuals who have lost a lot of electrolytes through exercise or use of diuretic medication, and then drink only water to make up for the fluid loss. If you fall into one of these categories, be aware of electrolyte loss and augment your water consumption with an electrolyte drink.

What you can take from this research is to following. Staying properly hydrated is important not only for the many reasons that we already knew, it is also important if you want to have proper mental clarity and focus. Who would have thought that symptoms such as fatigue, tension, impaired memory, mood swings and anxiety could appear as symptoms of dehydration, even before the thirst sensation kicks in?

My advice? If you are feeling tense, tired, anxious, foggy or just downright bitchy…. have a drink!!!  Water that is!    🙂

The Journal of Nutrition: Armstrong, L.E. et al, Mild Dehydration Affects Mood in Healthy Young Women, Dec. 2011, vol. 142 no. 2 382-388

British Journal of Nutrition, Ganio, Matthew, S. et al, Mild dehydration impairs cognitive performance and mood of men, November 2011, 106: pp 1535-1543

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About The Author
Brian Fulton
Brian Fulton Brian Fulton has been a Massage Therapist in Ontario Canada since 1999. His approach toward health and the human body is broad and holistic in nature. Brian is also the author of The Placebo Effect in Manual Therapy: Improving Clinical Outcomes (available on Amazon)