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Air con led to quicker thinking during heat wave

12 Jul 2018
Photo of sun and clouds. Courtesy: iStock/ELyrae
Courtesy: iStock/ELyrae

Students living without air con during a heatwave in the US performed worse in cognitive tests than students with air con. The study is the first to show the detrimental effects of indoor temperatures during a heat wave on young, healthy individuals’ thinking, according to the researchers.

“Most of the research on the health effects of heat has been done in vulnerable populations, such as the elderly, creating the perception that the general population is not at risk from heat waves,” said Jose Guillermo Cedeño-Laurent of Harvard T H Chan School of Public Health, US. “To address this blind spot, we studied healthy students living in dorms as a natural intervention during a heat wave in Boston. Knowing what the risks are across different populations is critical considering that in many cities, such as Boston, the number of heat waves is projected to increase due to climate change.”

Extreme heat is the leading cause of death of all meteorological phenomena in the US. Most previous research on the health impacts of extreme heat has used records of outdoor temperature. In the US adults spend 90% of their time indoors, however.

Cedeño-Laurent and colleagues asked 44 students in their late teens and early 20s to take tests on their smartphones first thing in the morning. The students had to describe the colour of displayed words, which assessed cognitive speed and ability to focus on relevant stimuli, and answer arithmetic questions, testing cognitive speed and working memory. The tests took place on 12 days in the summer of 2016; after five days there was a five-day-long heat wave followed by a two-day cooldown.

A total of 24 students lived in six-storey housing built in the early 1990s with central air con. The other 20 lived in low-rise buildings from 1930 – 1950 without air con. The team put a device to measure temperature, carbon dioxide levels, humidity and noise in each student’s room, and the students wore devices to track their physical activity and sleep.

During the heat wave, students living without air con had reaction times for the word-colour tests 13.4% longer than the students with air con. The students without air con also scored 13.3% lower on the addition and subtraction test. Together, the data showed that students in rooms with air con were both faster and more accurate in their responses.

The students’ cognitive performance differed most during the cooldown period, when outdoor temperatures began to drop but indoor temperatures remained high in the dorms without air con.

“Indoor temperatures often continue to rise even after outdoor temperatures subside, giving the false impression that the hazard has passed, when in fact the ‘indoor heat wave’ continues,” said Joseph Allen of Harvard T H Chan School. “In regions of the world with predominantly cold climates, buildings were designed to retain heat. These buildings have a hard time shedding heat during hotter summer days created by the changing climate, giving rise to indoor heat waves.”

 The researchers published their findings in PLOS Medicine.

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