Study Shows Heat Hurts Cognitive Ability

Researchers put young people in old, hot dorms during a Boston heat wave, and found that their memories and cognitive speed was worse that their AC-chilled counterparts.
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Summer of 2016 was brutal—it broke two centuries of heat wave records, as the hottest year ever recorded. But that made it the perfect time to study how heat affects young, relatively healthy, probably very stinky and sweaty students living without air conditioning.

Turns out, suffering through a heat wave makes even the most resilient among us a little dull.

Researchers led by the Harvard T.H Chan School of Public Health studied how indoor temperatures impacted 44 students in their late teens and early 20s living for 12 days in Boston dorms. They found that people living in air conditioned environments performed better on math and memory tests than those forced to sweat it out.


Their findings are published today in PLOS Medicine.

Most research on heat and health focus on vulnerable populations: The elderly, sick, or very young, groups for which extreme heat can be deadly. This is the first field study on the effects of a heat wave on young, healthy individuals, Jose Guillermo Cedeño-Laurent, research fellow at Harvard Chan School and lead author of the study, told me in a phone call. They sought to study heat in a “real setting, in real life,” he said.

The student-participants were separated into two kinds of buildings: One group lived in six-story dorms built in the early 1990s and had central AC, while the others were in low-rises that were constructed between 1930 and 1950 and did not have AC. They picked their housing preferences on a first-come, first-serve basis. (Feel bad for the ones who got in late.)

The students were asked to take tests on their smartphones in the mornings when they woke up. One test asked them to quickly and correctly identify the colors of words, and the other asked them to do basic math problems. During the hottest days of that span, the students in the non-air conditioned building were 13 percent slower on the color-word tests, and 13 percent worse at the math tests. The ones chilling in the AC were faster and more accurate on their tests.

As heat waves get hotter and more frequent around the world due to climate change, the researchers write that they’re hoping studies like this one illustrate how bad it can get for even the most healthy among us. Cognitive function deficits “extend to larger sectors of the population and can have significant implications on educational attainment, economic productivity, and workplace safety,” they write in the study.

“By making the findings relatable to any of us, it makes the issue of climate change personal,” Cedeño-Laurent told me. “We on purpose elected this population because it’s normally considered to be resilient to heat exposure, but we found the effects on them… [suggesting] that these are effects that could be seen widely on the general population.”

And as we plug in and crank up our AC units every summer, we create a vicious cycle of damaging the environment with ozone-depleting refrigerants and energy consumption. We need better regulations around how we build energy-efficient buildings, and what goes into our ACs, the researchers say.

“This is a great opportunity for the US to show its leadership,” Cedeño-Laurent said. “This is low hanging fruit in the fight against climate change.”