Your Brain Feels the Heat, Even if You Don't

2018 is shaping up to be the fourth-hottest year on record (after 2016, 2015, and 2017). In light of that, we thought we’d take a moment to highlight reporting from last month on two studies which looked at how the brain is affected by two everyday heat-related factors: dehydration and air temperature.

First, here is NPR on an analysis by researchers at the Georgia Institute of Technology of 33 studies, who found that even mild dehydration can influence myriad aspects of brain functionality, from mood to cognition. The level of dehydration at which these effects begin to manifest is just 1.5% (of body mass loss), a degree which can result from as little as 30 minutes of moderate-to-strenuous exercise. For a person of average size, 1.5% dehydration means losing more than a pint of water, but many people do not yet feel thirst at that stage.

Overall, Millard-Stafford found that dehydration impairs cognitive performance, especially in the domains of attention, executive function (the part of the mind one uses to solve unforeseen problems and see others’ points of view, among other things), and motor coordination, and that this impairment grew more serious when the level of dehydration exceeded 2%.

A second NPR piece from earlier in July reported on a study authored by Harvard University researchers which aimed to learn how indoor air temperature affects many of those same domains. The study used an innovative method: each morning, the students who made up the two testing groups would take tests measuring attention, processing and cognitive speed, and memory which had been pushed to their cell phones overnight. One group lived in an air-conditioned dormitory with an indoor temperature of 71 degrees; the other lived in a dorm without air conditioning, where the indoor temperature averaged just below 80 degrees.

The students living in the dorm without air conditioning were found to have responses which were both slower and more often incorrect than those of their cooler peers. As indicated in the report, these results reinforce the findings of a number of studies in the past decade air temperature’s effect on cognition in adults (in whom it has frequently been examined through the lens of office productivity), and in young people (in whom it has been scrutinized as a variable in standardized test performance).