Study finds dehydration affects our brains

ATLANTA - We know we should be drinking at least 6 to 8 glasses of water a day, but many of us don't.

Georgia Tech researchers say it may be time to rethink how much fluid we're drinking.

They found dehydration can make it harder to pay attention and think clearly, especially when we're performing a repetitive task, like driving a car or staying focused on the job.

To find out how fluid loss affects brain function, Dr. Mindy Millard-Stafford, Director of Georgia Tech's Exercise Physiology Lab, and Matt Wittbrodt, a former Tech research assistant, tracked 13 healthy volunteers. They agreed to exercise, get dehydrated and then go through a monotonous test to measure how well they were able to focus on pushing a button for about 20 minutes.

"And it was pretty boring," Wittbrodt says.  "So, it also stressed their ability to pay attention over that 20 minutes."

The researchers found that even being mildly dehydrated, or losing 2 percent of their body weight, caused the volunteers to make more mistakes.

"So, a 200-pound athlete, who loses 4 pounds (of fluid), which is pretty easily done in the summer in Atlanta, under those conditions, if they don't rehydrate. they would probably have an impact on their mental performance," Millard-Stafford explains.

Just exercising in the Georgia heat dropped the volunteers' score by 8 percent.

The fluid loss, doubled the affect, dropping their ability to stay on task by 16 percent,

"That 16 percent decrease in performance is a pretty big decrease, especially if you're in an occupation where one mistake could have catastrophic consequences," Wittbrodt says.

And there's another reason to drink up.

Wittbrodt and Millard-Stafford used a functional MRI machine to look for changes in the dehydrated volunteers' brain structure. Wittbrodt says they saw signs their brains were stressed by competing challenges:  trying to pay attention to the task at hand, pushing the button, while trying to relieve the fluid imbalance.

"You have this cognitive demand that says, 'I need to complete this task,' Wittbrodt explains.  "And, we then also have the demand that says, 'I'm thirsty, I don't feel very good, and I need to rectify this.'

An area of the brain known as the thalamus, which relays sensory information, shrank on the fMRI images, while fluid-filled areas known as ventricles expanded with dehydration.

"It was remarkably consistent," Wittbrodt says.  "Every person who was dehydrated had their ventricles expanding, so we know it happens."

The researchers aren't sure why the volunteers' brains changed shaped.

Wittbrodt thinks the changes are a sign their brains were stressed by competing challenges.

"You have this cognitive demand that says, 'I need to complete this task,' Wittbrodt explains.  "And, we then also have the demand that says, 'I'm thirsty, I don't feel very good, and I need to rectify this.'

Millard-Stafford says most of us can rely on our thirst to tell us when we need to drink more fluid.

If you're going to be out in the Georgia heat, she recommends drinking water before and after you head outdoors.

"Also make sure your urine doesn't get bright gold and concentrated," she says. "That's another great way of understanding if you're getting sufficient fluid."