by David Le Blanc
As the global population braces for additional changes in climate over the next several decades, many have wondered how these changes might affect human health. Naturally, the conversation quickly turns towards how changes in the climate might affect sleep. Quality sleep is pivotal to overall human health -- emotional, psychological and physiological. The NCBI-published study “Effects of Thermal Environment on Sleep and Circadian Rhythm” originally found in the Journal of Physiological Anthropology explains how interconnected sleep is with all functions of the body. Researchers Kazue Okamoto-Mizuno and Koh Mizuno note that “sleep is involved in healing and repair of your heart and blood vessels” among other reparative processes.
The two researchers write that not only is sleep necessary for health, but lack of quality sleep is extremely harmful. Okamoto-Mizuno and Koh Mizuno write that “ongoing sleep deficiency is linked to an increased risk of heart disease, kidney disease, high blood pressure, diabetes, and stroke.” This study and others found that sleep quality -- and resultant overall health -- is impacted significantly by changes in climate. This is especially true of uncomfortable increases in temperature, begging the question: how will the changing climate affect sleep and human health moving forward? Follow below to learn more about how climate affects sleep and how impending changes might further impact our health.
Climate and Health: A Self-Reinforcing Cycle
Fatal Physical Consequences of High Temperature Exposure
According to the WHO -- World Health Organization -- human health is negatively affected by changes in the climate in a number of key ways, both direct and indirect. The WHO brief “Climate Change and Health” notes that “climate change affects the social and environmental determinants of health – clean air, safe drinking water, sufficient food and secure shelter.” Due significantly to temperature increases across the globe, the WHO expects “climate change...to cause approximately 250 000 additional deaths per year, from malnutrition, malaria, diarrhea and heat stress” between “2030 and 2050.”
According to the WHO, the increase in the number of days during which extreme heat occurs will harm a shocking percentage of our population. This is because extreme heat contributes “directly to deaths from cardiovascular and respiratory disease, particularly among elderly people.” High temperatures also increase the amount of ozone in the atmosphere and create a hospitable environment for additional pollutants -- e.g. “pollen and other aeroallergen levels.”
Non-Fatal Physical Consequences of High Temperature Exposure
A recent Business Insider article outlined the non-fatal consequences of repeated exposure to high temperatures. In her article “A massive heat wave is sweeping the US. Here's how extreme summer heat affects your body and brain” for Business Insider, Aria Bendix writes “warming has serious effects.” These effects are not solely limited to extreme physical health issues, but also affect “mental well-being and cognitive ability.” Bendix explains that when the human body is exposed to extreme temperatures repeatedly, it “becomes more susceptible to exhaustion and heat stroke.”
Aria Bendix notes that -- in the short-term -- the human body might experience “heavy sweating, clammy skin, dehydration, tiredness, headache, dizziness, nausea, cramps, and a quick, weak pulse” as a result of increased body temperature. People exposed to high heat might also begin to experience brain fog, writes Bendix, affecting work, relationships, ability to drive and so much more. The Business Insider writer explains that many studies have shown “as temperatures climb, humans perform more slowly and more inaccurately on cognitive tests.”
Mental and Brain Health Consequences of High-Temperature Exposure
Air pollution -- which increases significantly in higher temperatures -- also severely impacts cognition and emotional health. In her article “Smog in Our Brains” for the American Psychological Association, Kirsten Weir writes that “over the past decade, researchers have found that high levels of air pollution may damage children's cognitive abilities.” High levels of air pollution also “increase adults' risk of cognitive decline and possibly even contribute to depression.” Weir references a study conducted by Randy Nelson, PhD -- an OSU neuroscience professor -- to support the link between depression and air pollution. In his study, Dr. Nelson reviewed the responses of mice to pollution exposure. Nelson and his team found that “mice exposed to the polluted air scored higher on tests of depressive-like responses.” The mice also experienced physical changes in brain structure -- further outlining the dystrophic effects of pollution.
Why is Sleep Important for Human Health?
As we already know, the quality and quantity of sleep attained by humans directly impacts their overall health. In their brief “Sleep Deprivation and Deficiency,” the NIH’s National Heart, Lung and Blood Association outlines the positive effects sleep has on the body. According to the NIH brief, quality sleep decreases “the risk of obesity” and “helps maintain a healthy balance of the hormones” that control hunger. Quality sleep also reduces the risk for diabetes by affecting “how your body reacts to insulin.” Sleep -- particularly deep sleep -- also supports normal growth, cell repair and fertility. Perhaps most importantly -- particularly during a global pandemic -- sleep provides significant support to the immune system, helping humans fight “common infections.”
How Climate Affects Sleep
According to Robinson Meyer in his article “Climate Change Is Already Making Americans Sleep Worse” for The Atlantic, “unusually warm nights are a public-health hazard” because of the ways in which they impact sleep. Meyer writes that “sleep is regulated pretty heavily by our body temperature—and especially by our core body temperature.” Meyer’s article for The Atlantic references the recent Science Advances study “Nighttime temperature and human sleep loss in a changing climate.” The study -- conducted by primary researcher Nick Obradovich and his team -- “investigate[d] whether anomalous nighttime temperatures harmed the sleep quality of individuals.”
Obradovich questioned if “climate change—through increases in nighttime heat—[will] disrupt sleep in the future?” Nick Obradovich explains in the study that “normal sleep-wake cycles are governed by...thermoregulation.” A “decrease in core body temperature” is necessary for preparing the body for quality sleep. If the core body temperature is too high, “the normal physiology of sleep” will inevitably be interrupted. Overall, the Science Advances study found that “as temperature anomalies become more positive, the incidence of nights with insufficient sleep increases.”
For tips on how to make hot nights more comfortable -- and quality sleep more achievable -- in homes without air conditioning, continue to Olive + Crate’s article on the topic.