Even little dehydration can negatively affect mood and thinking, suggests findings from a growing body of evidence. Being just a little dehydrated is linked to a type of indirect effects like mood changes or muddled thinking.

Mindy Millard-Stafford who published an analysis of the evidence this month said that when people are a little bit dehydrated they often don’t perform their regular tasks efficiently those requires their complex processing or their attention. Mindy is a director of the Exercise Physiology Laboratory at Georgia Institute of Technology and her analysis is based on 33 studies.

Studies show that outdoors exercising will make your mildly dehydrated in the summer heat. Harder running can bring a person’s dehydration level to 2 percent in about 30 minutes, according to Doug Casa, a professor of kinesiology at the University of Connecticut, and CEO of the Korey Stringer Institute.

“Most people don’t realize how high their sweat rate is in the heat,” Casa says.

For the findings, researchers recruited participants including young, healthy and active women. Participants performed a bunch of cognitive tests and as well as agreed to follow a diet which restricts their fluid intake to no more than six ounces per day.

When conducting one of the tests that included a card game, designed to measure cognitive flexibility, the researchers found that dehydrated women had about 12 percent more total errors in the game. While their performance improved after they drank sufficient water.

“I absolutely think there could be big implications of having a mild cognitive deficiency with small amounts of dehydration,” Casa notes.