How Heat Waves Affect Your Brain

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As heat waves roll across the U.S. in the summer, heat-related illnesses are a serious threat to Americans. Although we often hear about the dangers of overheating and dehydration, heat waves lead to even broader consequences for the people coping with them. A "heat dome” covered the East Coast and southern U.S. last month, and has now shifted to California.

A broad body of research shows extreme heat affects our ability to think and reason, and new studies this year have verified that heat affects cognition.

A new, longitudinal study in China used results from a cognitive test of the China Family Panel Study and matched it with weather data at the testing locations. Researchers found a significant decrease in math test scores when temperatures reached over 89 degrees compared to between 70 and 75 degrees. Test-takers living in warmer climates were affected less by the warmer temperatures, suggesting they were able to adapt to the heat.

A second study published this year investigated the cognitive performance of firefighters exposed to extreme heat. The review looked at seven studies of firefighters and found that acute heat stress did not impair simple cognitive tasks, such as memory recall and basic arithmetic. However, the study authors did find that extreme heat affected complex cognitive tasks, such as vigilance and working memory.

These new studies build on previous research that finds high temperatures affect how our brains function. A systematic review published in 2019 looked at how heat stress affected cognition in members of the U.S. military. Similar to the review of studies on firefighters, researchers found that heat stress impacted cognitive performance, especially at higher temperatures, during longer exposures and more complex cognitive tasks. This was especially true when heat stress was combined with another factor, such as physical activity.

An earlier systematic review came to the same conclusion: Heat stress significantly impacts people’s ability to complete complex cognitive tasks. This review found when participants felt hotter, less comfortable, and more irritable due to heat exposure, they performed worse on the complex cognitive tasks. This suggests that each person’s physical response to heat exposure is an important factor to consider. This review also found that cooling interventions, such as cooling packs placed on the skin and nutritional supplements to boost cognition, helped to alleviate some of the cognitive changes experienced during heat.

There is also evidence that heat affects our mental health. A 2022 study found an 8 percent increase in emergency department visits for mental health problems on the hottest days of the year compared to the coolest days. People are more likely to come to the hospital for self-harm, substance use, anxiety, and mood disorders as temperatures increase, the study found.

Medical experts believe the higher temperatures affect the brain chemicals—specifically serotonin and dopamine levels—that help to regulate mood, cognitive function, and our ability to perform complex tasks. Higher temperatures also lead to irritability and psychological distress, which are contributing factors to substance abuse and suicide. The clear evidence that exposure to high temperatures negatively impacts cognitive function likely explains the increased hospitalizations for dementia.

What’s the best way to preserve cognition when temperatures soar? Experts say to follow the same steps you would to prevent heat-related illnesses.

• If you don’t have air-conditioning in your home, consider going to a cooling center or public place with air-conditioning such as a library or mall.
• Take cool showers or baths.
• Wear loose, lightweight, light-colored clothing.
• Use your oven less to help reduce the temperature in your home.
• If you are outside, try to stay in the shade and use a hat.
• Drink plenty of fluids.
• Avoid activities or working outdoors during the warmest parts of the day.

The take-home message: Heat-related illnesses aren’t the only dangers during heat waves. Extremely warm temperatures also affect complicated cognitive tasks.