Heat and Your Brain

“What dreadful hot weather we have! It keeps one in a continual state of inelegance.”

~ Jane Austen.

The dry hot desert season is here, and there is finally an actual reason to complain about the heat. With afternoon temperatures well past 100°F, stepping outside can feel like a physical wallop. Our bodies are quite efficient at maintaining homeostasis in the face of environmental variations. However, enough heat exposure will eventually lead to increased body temperature, sweating, clammy skin, dehydration, fatigue, nausea, vomiting, and cramps. And it is not just the body that suffers. Extreme heat can affect the nervous system, causing headaches, dizziness, impaired balance, confusion, and loss of consciousness.

As for why the body and brain overheat, much of the blame falls on a part of the brain called the hypothalamus, which is responsible for maintaining optimal body temperature. When it is hot, the hypothalamus signals the body to start sweating. Excessive sweating to maintain body temperature can lead to dehydration and electrolyte imbalances which affect electrical conduction and keep nerves and the brain from working properly. Also, in some medical conditions like multiple sclerosis, the hypothalamus does not work as well as it should, so heat exposure results in significant problems for proper neurological function. In anyone, high enough temperatures cause the blood-brain barrier to break down so that unwanted proteins and ions build up in the brain, thus producing inflammation and symptoms of heat stroke. Eventually, protein structure starts to unfold, causing permanent injury and cell death in parts of the brain.

Even when heat stress is not quite so extreme, it affects cognitive and mental functioning, possibly through altered perfusion and metabolism in various parts of the brain. A 2018 study in the journal Nature Climate Change reported that people were more likely to express depressive feelings as temperatures rose, and that a 1°C rise in average monthly temperature was associated with an increase in the monthly suicide rate. Several studies show that as temperatures climb, we perform more slowly and inaccurately on cognitive tests and tasks.

In 2006, researchers evaluated how well participants carried out common office tasks and saw a consistent decrease in work productivity when the temperature rose above 75.2°F. In 2016, researchers studied college students, half of whom lived in buildings with air conditioning, where indoor temperature averaged 71°F, and the other half lived in dorms without air conditioning, where air temperature averaged 80°F. Over several days, researchers administered tests that included basic math problems and questions that measured attention and processing speed. Students in the buildings without air conditioning had slower reaction times, lower scores, and fewer correct responses on simple math tests. Fortunately, the impact of heat on cognitive performance appears temporary, and cooling mitigates it.

One fascinating potential heat effect on the brain that would be harder to combat is that the brain may get larger in the warm months. Researchers from Hartford, Connecticut, studied over 3,000 healthy people over a 15-year period. MRI scans showed brain volume increased as temperatures warmed during spring and summer and decreased in the colder months. Researchers believe that blood flow changes due to barometric pressure and air temperature affect brain volume. Hmm, maybe your head is as big and heavy as it feels with that awful June afternoon headache!

Anyway, this summer, be extra kind to your brain. Drink lots of water; use air conditioning and fans; wear light, loose clothing, and a hat in the sun; and stay in during the hottest times of day.

Post by: Nadia Fike

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Read more:

1. Book, G. et al. Effects of weather and season on human brain volume. PLOS One. March 24, 2021. https://doi.org/10.1371/journal.pone.0236303 2. Burke, M. et al. Higher temperatures increase suicide rates in the United States and Mexico. Nature Clim Change 8, 723–729 (2018). https://doi.org/10.1038/s41558-018-0222-x 3. Cedeno Lurent, G. et al. 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. PLOS. July 10, 2018. https://doi.org/10.1371/journal.pmed.1002605