With record-breaking heat waves affecting much of the United States this summer, experts are warning about the hidden dangers of dehydration.Now a new study finds dehydration not only impairs people physically. It can also lead to cognitive decline.According to the recent study from the Georgia Institute of Technology in Atlanta, just a couple of hours of vigorous activity in the heat without drinking fluids or eating can greatly affect concentration.

Researchers found that dehydrated people taking tests which required attention to details or tests that were monotonous were most affected.

Functions such as complex problem-solving, coordination, and attention suffered the most, while activities involving quick reactions weren’t as affected.

“The simplest reaction time tasks were least impacted, even as dehydration got worse, but tasks that require attention were quite impacted,” said Mindy Millard-Stafford, PhD, director of the exercise physiology laboratory, a professor in Georgia Tech’s School of Biological Sciences, and a co-author of the study, in a released statement.

The authors state that maintaining focus in long meetings, driving a car, or having a monotonous job in a hot factory requires attention.

However, in the face of being dehydrated, these abilities decline, and diminished cognition can pose harm to the body.

What did they find?

To understand how heat affects cognition, the researchers analyzed data from 33 peer-reviewed research papers, which involved 413 participants. The team looked at test results of executive function, attention, motor coordination, and reaction time to specific tasks.

As the participants lost more water, they increasingly made more errors during attention-related tasks. For example, those activities that were more repetitive and unexciting, such as punching a button in various patterns for several minutes, suffered the most.

Although researchers don’t know exactly when cognitive impairments occur, they examined studies that involved between 1 and 6 percent loss of body mass due to dehydration.

They found that the most severe impairments occurred starting at 2 percent, and this drop in water weight can occur quickly.

“If you weigh 200 pounds and you go work out for a few of hours, you drop 4 pounds, and that’s 2 percent body mass,” Millard-Stafford said. “With an hour of moderately intense activity, with a temperature in the mid-80s, and moderate humidity, it’s not uncommon to lose a little over 2 pounds of water.”

Some of the earliest signs of dehydration include being thirsty, feeling dizzy, developing nausea, and headaches. When someone starts to develop heat cramps, it may be an early indicator of the progressive effects of dehydration.

In extreme cases, when dehydration isn’t prevented or effectively treated at home, many people end up having to go to the emergency department.