Dehydration can impair your ability to think clearly, a new study suggests. Researchers found that athletes who lost fluid equal to 2% their weight took a hit to their cognition. Even this mild to moderate level of dehydration - the loss of 2 pounds for someone who weighs 100 pounds and four pounds for someone weighing 200 - led to attention problems and impaired decision making, according to the report in Medicine & Science in Sports & Exercise. In particular, dehydration led to impairment in tasks requiring attention, motor coordination, and so-called executive function, which includes things like map recognition, grammatical reasoning, mental math, and proofreading, for example. “We’ve known that physical performance suffers at a threshold of 2% of body mass, particularly when it’s from exercise in a warm environment,” said study coauthor Mindy Millard-Stafford, a professor in the School of Biological Sciences and director of the physiology lab at the Georgia Institute of Technology.
