Can't cool off this summer? Heat waves can slow us down in ways we may not realize.
New research suggests heat stress can muddle our thinking, making simple math a little harder to do.
"There's evidence that our brains are susceptible to temperature abnormalities," says Joe Allen, co-director of the Center for Climate, Health and the Global Environment at Harvard University. And as the climate changes, temperatures spike and heat waves are more frequent.
To learn more about how the heat influences young, healthy adults, Allen and his colleagues studied college students living in dorms during a summer heat wave in Boston.
Half of the students lived in buildings with central AC, where the indoor air temperature averaged 71 degrees. The other half lived in dorms with no AC, where air temperatures averaged almost 80 degrees.
"In the morning, when they woke up, we pushed tests out to their cellphones," explains Allen. The students took two tests a day for 12 consecutive days.
One test, which included basic addition and subtraction, measured cognitive speed and memory. A second test assessed attention and processing speed.
"We found that the students who were in the non-air-conditioned buildings actually had slower reaction times: 13 percent lower performance on basic arithmetic tests, and nearly a 10 percent reduction in the number of correct responses per minute," Allen explains.
The results, published in PLOS Medicine, may come as a surprise. "I think it's a little bit akin to the frog in the boiling water," Allen says. There's a "slow, steady — largely imperceptible — rise in temperature, and you don't realize it's having an impact on you."
The findings add to a growing body of evidence that documents the effect of heat on mental performance, both in schools and workplaces.
For instance, a 2006 study from researchers at Lawrence Berkeley National Lab found that when office temperatures rise above the mid-70s, workers' performance begins to drop off. Researchers reviewed multiple studies that evaluated performance on common office tasks. The study found that worker productivity is highest at about 72 degrees. When temperatures exceeded the mid-80s, worker productivity decreased by about 9 percent.
Another, more recent study compared worker performance in green-certified buildings and typical office buildings. They found a dip in cognitive function linked to conditions in the indoor environment, including higher indoor temperatures and poor lighting.
And, when it comes to performance in the classroom, a study funded by the Harvard Environmental Economics Program finds that taking a standardized test on a very hot day is linked to poorer performance. The study includes an analysis of test scores from students in New York City who take a series of high-school exams called the Regents Exams.
The author, R. Jisung Park, assistant professor at the University of California, Los Angeles, writes that compared with a 72-degree day, "taking an exam on a 90◦F day leads to a 10.9 percent lower likelihood of passing a particular subject (e.g. Algebra), which in turn affects probability of graduation."
There's still a lot to learn about how our brains and bodies respond to heat. "We all tend to think we can compensate, we can do just fine" during heat waves says Allen. But he says the "evidence shows that the indoor temperature can have a dramatic impact on our ability to be productive and learn."
DAVID GREENE, HOST:
For now, we’re going to turn to a story about a heat wave that is affecting much of the country this summer. NPR’s Allison Aubrey reports that all of this warmth can slow us down in ways we might not even realize.
ALLISON AUBREY, BYLINE: Angela Montes (ph) is in her mid-30s and very fit. Right now, she's training for Ragnar, a long-distance relay race. So when she went on a training run one afternoon last week in Oakland, Calif., where she lives, she never guessed that the unusually hot day would give her any trouble.
ANGELA MONTES: Two and a half miles in, I just started feeling really dizzy and nauseous. More than anything, I was just really, really nauseous, and then I just started vomiting.
AUBREY: After a few hours of rest in a cool place, she felt OK. But she says she was taken aback by the experience.
MONTES: When I imagine a heatstroke or heat-related illness, I actually imagine workers that are out working on the roads or farmers that are outside for hours a day.
AUBREY: Outdoor workers are at risk, but they can be more acclimated to the heat and may take precautions, such as staying hydrated. Jack Der-Sarkissian is a family doctor with Kaiser Permanente in Los Angeles. He's seen a lot of cases of heat-related illness similar to Angela Montes, people who work and live in air-conditioned spaces and are caught off guard when they exercise during a heat wave.
JACK DER-SARKISSIAN: Under normal conditions, they would feel fine, but under the heat, humidity, felt really ill. So that kind of came unexpectedly, and they think something else is going on.
AUBREY: It's not just our bodies that can feel lethargic during a heat wave. A new study from the Center for Climate, Health, and the Global Environment at Harvard finds high temperatures can muddle our thinking, too. Here's Joseph Allen, the co-director of the center. He says research on heat-related health effects tend to focus on the elderly, but this study is different.
JOSEPH ALLEN: Here, what we were interested in doing was trying to look at, what's the impact on a young, healthy, resilient population?
AUBREY: They studied students living in college dorms during a summer heat wave in Boston. Half of them lived in buildings that had central AC. The other half lived in dorms that did not.
ALLEN: So during the entire study, in the morning when they woke up, we pushed cognitive function tests out to their cellphones, and we have them take these standardized cognitive performance tests.
AUBREY: One was basic arithmetic. Another is designed to measure attention and cognitive speed.
ALLEN: And we found that the students who were in the non-air-conditioned buildings actually had slower reaction times - 13 percent longer reaction times, 13 percent lower performance on basic arithmetic tests and nearly 10 percent reduction in the number of correct responses per minute.
AUBREY: Now, the temperature difference was not huge - about 80 degrees in the un-air-conditioned dorms compared to 71 degrees in the modern dorms. But the surprise is that this difference in temperature can have a significant effect. Allen says people don't sense that their thinking has slowed down. It's subtle.
ALLEN: I think it's a little bit akin to the frog in boiling water - this slow, steady, largely imperceptible rise in temperature, and you don't realize it's having an impact on you.
AUBREY: There's a growing body of evidence that documents the impact of heat on performance both in schools and workplaces. For instance, researchers at the Lawrence Berkeley National Laboratory found that when office temperatures rise above the mid-70s, workers' performance begins to drop off a bit. And Allen and his colleagues have documented similar results.
ALLEN: When indoor temperature conditions are not in typically comfortable range, we perform 5 percent worse on cognitive function tests. So that's an impact you see just in a regular office building without even extreme temperature ranges.
AUBREY: Now, slowing down a bit is part of the fun of summer, so on weekends and vacations when we want to relax, we benefit from that, but at school and work, maybe not so much. So as our climate changes, Allen says, we need to be more aware of all the ways heat can influence our health and well-being. Allison Aubrey, NPR News. Transcript provided by NPR, Copyright NPR.