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 an internationally acknowledged integrative health and mindfulness specialist, best-selling author of 16 fitness and wellness books translated into multiple languages and sold worldwide, award-winning health journalist, contributing editor to Fitness Journal, media spokesperson, and IDEA's 2008 Fitness Instructor of the Year. She's a 25-year industry veteran and former health and fitness educator at the Stanford Prevention Research Center, who has served on multiple industry committees and co-authored trade books and manuals for ACE, ACSM and YMCA of the USA. She has appeared on TV worldwide and was a featured trainer on America's Next Top Model.

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