Is Dehydration Making Your Brain Lazy?


Can being dehydrated make you stupid? Dr. Briffa did a piece on his blog earlier this month talking about how dehydration can actually cause the brain to stop functioning properly. He says in his practice, he’s seen how dehydration can cause lethargy, particularly mental lethargy. And you can’t navigate the world in an effective way if you’re suffering from a lazy brain!

Past studies may have confirmed this by inducing dehydration in subjects through heat and/or exercise and finding brain function to be impaired. However, we can’t draw firm conclusions from these studies since the impaired cognitive function could have resulted from the heat or the exercise and not the dehydration itself.

In a new study, published in the British Journal of Nutrition, the authors controlled for these factors to see if dehydration really does impair the functioning of your brain. They subjected participants in the study to three different conditions on separate occasions. In the first condition, subjects walked on a treadmill at a steep incline and were given a diuretic drug to increase dehydration. In the second condition, the subjects did the same treadmill exercise, but were not given the drug (but were still deprived of water). In the third instance, the subjects did the same exercise again, but this time were kept hydrated with water.

The three different conditions were essentially done to test different levels of dehydration (the “drug group” being the most dehydrated, the “water group” being not dehydrated at all), while having equal levels of exertion and equal exposure to heat. After each of the trials, the subjects were given tests to assess mental function, fatigue level and mood.

Researchers found the more dehydrated the subjects were, the worse their “working memory,” which Briffa defines as: “The ability to actively hold information in the mind needed to do complex tasks such as reasoning, comprehension and learning.” The researchers also found levels of fatigue and measures of tension and anxiety were all greater the more dehydrated the participants were.

This study shows being dehydrated can actually make you less mentally capable while making you tired and negatively affecting your mood. Three good reasons to make sure you’re getting enough water. It would be a real shame to not be as mentally competent as you could be.

But how much water is enough? To say “drink when you’re thirsty” is generally pretty good advice, but if you’re getting to the end of the day hardly having drank any water, you may not be recognizing your own body’s thirst signals. One and a half to two liters is a pretty good reference — if you’re around that, you’re probably OK.

But don’t force feed yourself water just to hit a the target number of “eight glasses per day.” Remember that lots of things can affect your water needs. Environmental factors like your exercise level, your health conditions as well as the heat and humidity — all affect how much water you need to take in. Similarly, a six foot tall, 220-pound man is going to have higher requirements than a 5’6″ woman (both gender and size affect water needs). Diuretic beverages, including ones with caffeine or alcohol, also increase water needs.

The Healthy Foodie is Doug DiPasquale, Holistic Nutritionist and trained chef, living in Toronto

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