If you spend just two hours in the sun doing yard work without drinking any water, your cognitive abilities will start to decline. A new study found that cognitive functions like attention, coordination and complex problem solving diminishes as the body becomes dehydrated.

Researchers analyzed the data from multiple peer-reviewed research papers on the topic of dehydration and cognitive ability.

They found that while concentration was affected by dehydration, the ability to react quickly was not.

“The simplest reaction time tasks were least impacted, even as dehydration got worse, but tasks that require attention were quite impacted,” says Mindy Millard-Stafford, a professor in the School of Biological Sciences at Georgia Tech.

Multiple studies reviewed showed that dehydration caused participants to make errors during repetitive tasks that required attention, such as pressing a button in a specific pattern.

“Maintaining focus in a long meeting, driving a car, a monotonous job in a hot factory that requires you to stay alert are some of them,” says Millard-Stafford, the study’s principal investigator. “Higher-order functions like doing math or applying logic also dropped off.”

The authors, who were concerned about the risk of accidents while dehydrated, published their findings in the journal Medicine & Science in Sports & Exercise.

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