How Dehydration Affects Mental Acuity

Research shows that excessive heat can not only make your lethargic, it can slow your brain too.

How Dehydration Affects Mental Acuity

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Summer’s fast approaching, and with it comes the dangers of dehydration. Not only is it easy to become mildly dehydrated without knowing it, it can affect brain function as well as your body.

 In fact, there is a growing body of evidence that being just a little dehydrated is tied to a range of subtle effects, ranging from mood swings to a scrambled thought process. According to Mindy Millard-Stafford, director of Exercise Physiology Laboratory at Georgia Institute of Technology, when people are mildly dehydrated they don't do as well on tasks that require complex processing or on tasks that require a lot of their attention. 

How long does it take to become mildly dehydrated in the summer heat? 

Not long at all, studies show, especially when you exercise or engage in strenuous activities outdoors. Studies have shown that hiking at moderate intensity for one hour, can cause a person to reach about 1 ½- to 2 percent dehydration. For an average-sized person, 2 percent dehydration equates to sweating out about a liter of water. And most people don't realize how high their sweat rate is in high heat, studies show. For example, if you're running or hiking hard, that level can be reached in just 30 minutes. Also, at this level of dehydration, the feeling of thirst for most of us is just beginning.

How Much Water Do We Need? 

There are no exact daily requirements, but there are general recommendations. A panel of scholars convened several years ago by the National Academies of Sciences, Engineering and Medicine concluded that women should consume, on average, about 91 ounces of total water per day. For men, the suggested level is even higher at 125 ounces.

Note that this total includes water from all sources, including food and other beverages, such as coffee and tea. Typically, people get about 20 percent of the water they need daily from fruits, vegetables and other food. Also, water needs vary from person to person. For example, body weight and muscle mass matter. Also, physical activity and heat exposure can increase the amount of fluid a person needs.

How Can You Tell if You're Dehydrated? 

One easy way to check is by looking at the color of your urine. As a general rule of thumb, the darker the color, the more likely you are to be dehydrated. A color chart developed by physiologist and University of Connecticut professor Lawrence Armstrong can be a helpful guide.

Remember that older people are more vulnerable to dehydration. And, as we age, we're not as good at recognizing thirst. There's also evidence that older adults are prone to the same dips in mental sharpness as anyone else when mildly dehydrated. Also, all of us should remember to not wait until we're thirsty to begin hydrating. A good rule of thumb is to sip fluids throughout the day. No need to chug huge amounts at one time; there are some risks to overhydrating as well

Can Coffee, Tea and Other Caffeinated Drinks Have a Dehydrating Effect? 

The short answer is, no. The most recent evidence finds that coffee provides similar hydrating qualities to water. In other words, yes, your morning cup of coffee or any other caffeinated beverage you prefer can help keep you hydrated.



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