How High Temperatures Are Affecting Human Health

Climate change combined with the El Niño phenomenon makes the summer of 2023 come extraordinarily early. The global average temperature in June this year has broken through the highest value recorded in June. In early July, it has broken the historical record for the highest temperature for two consecutive days, becoming the two hottest days on earth since records began.

High temperatures will accelerate the melting of glaciers, resulting in reduced food production and accelerated loss of biodiversity. But ordinary people must be most concerned about their own health problems, because high temperature will put huge pressure on the cardiovascular system and increase the risk of death for the elderly, weak, sick and disabled.

Specifically, high temperature will cause two significant changes in the human body, one is sweating, and the other is an increase in heart rate. The purpose is to reduce the body’s core body temperature (Tc), that is, the temperature of internal organs. If the core body temperature cannot be lowered, it will not only affect the various physiological functions of the body, but also cause the cardiovascular system to undergo a stress response due to overwhelm.

Usually, doctors mainly measure the patient’s core body temperature to predict the occurrence of stress response, but the core body temperature measures the temperature inside the large intestine, which is inconvenient to operate, so Dr. Rachel Cottle of Pennsylvania State University in the United States decided to find an alternative method to issue an early warning.

The researchers recruited 51 healthy young people, let them swallow a temperature sensor to accurately measure their core body temperature, and then let them do simple physical activities (such as walking) in a control room while measuring their heart rate. It turned out that when the ambient temperature gradually increased, their heart rate also increased, but it quickly peaked. At this time, if the ambient temperature continues to increase, their heart rate will start to increase again, and the rate of increase will become faster and faster. Even if the experiment is stopped, it will not drop. This shows that they have a stress response to the cardiovascular system.

The temperature turning point at which the stress response occurs is related to the humidity of the environment. If it is a dry environment, then the turning point of the temperature is 41°C; if the humidity of the environment is high, then the turning point of the temperature will drop to 34°C. More importantly, their core body temperature is still normal at this time, and it will not start to rise until 20 minutes later.

Dr. Cotter wrote up the results of the research and published it in the June 22, 2023 issue of the Journal of Applied Physiology . The article pointed out that core body temperature is not only difficult to measure, but also has a hysteresis effect. If a person finds that his heart rate starts to rise continuously, it means that his cardiovascular system stress response has already begun. At this time, measures should be taken quickly, otherwise it will be too late.

Of course, the occasional stress response may not be a big deal for young people, but it is not the same for older people. According to a study published in 2022, for every 1°C increase in ambient temperature, the mortality rate will increase by 2.1%, with the vast majority of deaths occurring in the elderly.

This is also confirmed by a paper published in the July 10, 2023 issue of Nature Medicine . The lead authors of the paper, from the Barcelona-based Institute for Global Health (IS Global), found that a European heatwave in the summer of 2022 would have killed 61,672 people over a three-month period.

One of the most valuable aspects of this study is the statistical approach the researchers employed. Because general hospitals seldom list high temperature as the direct cause of death, the researchers cooperated with the European Statistical Office (Eurostat) in Luxembourg to pull out the death data in recent decades, and then compared it with the temperature to calculate the cause of high temperature. The number of additional deaths, leading to the above conclusions.

The last serious heat wave in Europe was in 2003, when more than 70,000 people died from the heat. While the two numbers don’t exactly match up because of different metrics, the result shows that Europe is still not well prepared for hot weather.

According to the forecast of the International Meteorological Organization, the next few years will be El Niño years, and the high temperature weather is likely to intensify. Are you ready?