The Grapevine

Mild Dehydration Hard To Notice, But Can Still Impair Mental Performance

Having trouble focusing on your work? Ask yourself when you last had a glass of water today. According to a new meta-analysis, even mild dehydration can have an impact on your mental performance.

The study titled "Dehydration Impairs Cognitive Performance: A Meta-analysis" was published in the journal Medicine & Science in Sports & Exercise on July 10. 

Researchers at the Georgia Institute of Technology gathered 33 studies for the analysis, finding that being even mildly dehydrated can affect our mood and even our thinking.

"We find that when people are mildly dehydrated they really don't do as well on tasks that require complex processing or on tasks that require a lot of their attention," said lead researcher Mindy Millard-Stafford, director of the Exercise Physiology Laboratory at Georgia Tech.

Mild dehydration is said to occur when we lose more than 2 percent of the normal water volume of the body. For a person of average size, this would equate to sweating out a liter of water.

Survey results are mixed on whether people underestimate the importance of staying hydrated, but most of us may not even know when we cross this threshold. Mild dehydration does not take too long to kick in either, whether we are engaging in physical activity or merely dealing with summer heat. 

"If I were hiking at moderate intensity for one hour, I could reach about 1.5 percent to 2 percent dehydration," said Doug Casa, a professor of kinesiology at the University of Connecticut. And if you think resting indoors is enough to escape the risk, think again.

Another recent study, conducted by Harvard T.H. Chan School of Public Health, showed how heat can slow down the thinking power of students who lived in dorms without an effective cooling system. 

"Most people don't realize how high their sweat rate is in the heat," Casa added. 

Perceiving 1.5 percent dehydration can be hard since the symptoms may be too noticeable. Doctors have drawn attention to the summer heat, warning how dehydration may affect people who only drink water when a strong thirst prompts them to.

Infants, children, and older adults are at the highest risk of dehydration among all age groups. People with chronic illnesses (such as kidney disease or untreated diabetes) and those who spend a lot of time outside (especially in hot regions) are also at risk according to the Mayo Clinic.

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

The easiest way to find out whether you are drinking enough water is to note the color of your urine. A pale yellow or a pale straw color indicates you are good to go, while a darker yellow is a sign that you should increase your fluid intake.