Reduced cognitive function during a heat wave among residents of non-air-conditioned buildings: An observational study of young adults in the summer of 2016

Abstract

Background

In many regions globally, buildings designed for harnessing heat during the cold exacerbate thermal exposures during heat waves (HWs) by maintaining elevated indoor temperatures even when high ambient temperatures have subdued. While previous experimental studies have documented the effects of ambient temperatures on cognitive function, few have observed HW effects on indoor temperatures following subjects’ habitual conditions. The objective was to evaluate the differential impact of having air conditioning (AC) on cognitive function during a HW among residents of AC and non-AC buildings using a prospective observational cohort study.

Methods

We followed 44 students (mean age = 20.2 years; SD = 1.8 years) from a university in the Greater Boston area, Massachusetts in the United States living in AC ( n = 24) and non-AC ( n = 20) buildings before, during, and after a HW. Two cognition tests were self-administered daily for a period of 12 days (July 9–July 20, 2016), the Stroop color-word test (STROOP) to assess selective attention/processing speed and a 2-digit, visual addition/subtraction test (ADD) to evaluate cognitive speed and working memory. The effect of the HW on cognitive function was evaluated using difference-in-differences (DiD) modelling.

Findings

Mean indoor temperatures in the non-AC group (mean = 26.3°C; SD = 2.5°C; range = 19.6–30.4°C) were significantly higher ( p < 0.001) than in the AC group (mean = 21.4°C; SD = 1.9°C; range = 17.5–25.0°C). DiD estimates show an increase in reaction time (STROOP = 13.4%, p < 0001; ADD = 13.3%, p < 0.001) and reduction in throughput (STROOP = −9.9%, p < 0.001; ADD = −6.3%, p = 0.08) during HWs among non-AC residents relative to AC residents at baseline. While ADD showed a linear relationship with indoor temperatures, STROOP was described by a U-shaped curve with linear effects below and above an optimum range (indoor temperature = 22°C–23°C), with an increase in reaction time of 16 ms/°C and 24 ms/°C for STROOP and ADD, respectively. Cognitive tests occurred right after waking, so the study is limited in that it cannot assess whether the observed effects extended during the rest of the day. Although the range of students’ ages also represents a limitation of the study, the consistent findings in this young, healthy population might indicate that greater portions of the population are susceptible to the effects of extreme heat.

Conclusions

Cognitive function deficits resulting from indoor thermal conditions during HWs extend beyond vulnerable populations. Our findings highlight the importance of incorporating sustainable adaptation measures in buildings to preserve educational attainment, economic productivity, and safety in light of a changing climate.

Abstract

Jose Guillermo Cedeño Laurent and colleagues document the detrimental effects of heatwaves on cognition among a group of students

Author summary

Why was this study done?

• Heat waves (HWs) have devastating consequences for public health globally.

• Buildings can exacerbate temperature exposures during HWs by maintaining high indoor temperatures overnight even when high ambient temperatures have subdued.

• Prior experimental studies have documented the effects of temperature on cognitive function, but no field studies have observed how indoor temperatures during HWs impact cognition, even though adults in the United States spend upwards of 90% of their time indoors.

What did the researchers do and find?

• We evaluate the impact of having air conditioning (AC) during a HW on cognitive function among residents of AC and non-AC buildings using a prospective, observational cohort study.

• A cohort of university students was recruited from 2 campus residence types—AC ( n = 24) and non-AC ( n = 20)—and followed over 12 consecutive days in the summer of 2016.

• Students living in non-AC spaces experienced significant decrements on cognitive test performance. Results show an increase in reaction time (Stroop color-word test [STROOP] = 13.4%, p < 0001; 2-digit visual addition/subtraction test [ADD] = 13.3%, p < 0.001) and reduction in throughput (STROOP = −9.9%, p < 0.001; ADD = −6.3%, p = 0.08) during HWs among non-AC residents relative to AC residents at baseline.

What do these findings mean?

• Future studies are needed to understand the duration of these effects to determine how the implications could extend to larger sectors of the population and could have significant impacts on educational attainment, economic productivity, and workplace safety.

• Given that existing adaptation solutions (e.g., AC) represent a positive feedback loop amplifying the effects of climate change, our findings highlight the need to provide sustainable adaptation solutions to foster adequate cognition during extreme heat events.