Dehydration Impairs Cognitive Performance

Drink water to ward off brain fog.

By Shirley Archer, JD, MA
Oct 12, 2018

Keep reminding clients to drink plenty of fluids. New research shows that cognitive abilities—attention, coordination, complex problem solving and reaction time—begin to decline with as little as 1% loss of body mass from dehydration, with more severe impairments showing up at 2%. Dehydration affects attention first and with more severity than other cognitive abilities.

Principal investigator Mindy L. Millard-Stafford, PhD, director of the exercise physiology laboratory at Georgia Institute of Technology, Atlanta, said that cognitive abilities affected in the study included “maintaining focus in a long meeting, driving a car [and doing] a monotonous job in a hot factory that requires you to stay alert.” She added that “higher-order functions like doing math or applying logic also dropped off.”

Researchers based their findings on a review and meta-analysis of 33 studies with a total of 413 participants. “There’s already a lot of quantitative documentation that if you lose 2% in water, it affects physical abilities like muscle endurance or sports tasks and your ability to regulate body temperature,” said Millard-Stafford. “We wanted to see if that was similar for cognitive function.”

The study was published in Medicine & Science in Sports & Exercise (2018; doi:10.1249/MSS. 0000000000001682).


Shirley Archer, JD, MA

Shirley Archer, JD, MA, is the 2008 IDEA Fitness Instructor of the Year and is IDEA's mind-body-spirit spokesperson. She is a certified yoga and Pilates teacher and an award-winning author based in Los Angeles, California, and Zurich, Switzerland. Two of her books, The Walking Deck and The Strength and Toning Deck, are now featured as iPhone apps. Contact her at

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