Exposure to high temperatures reduces the ability to fight infection, a study has found.
It may increase inflammation in the body and interfere with the immune system's functions, increasing susceptibility to infections and worsening existing heart problems.
The study results were shared at the American Heart Association’s Epidemiology and Prevention in Chicago.
Daniel Riggs, lead study author and assistant professor of medicine at the University of Louisville, told The National: “Exposure to heat results in physiological stress and high temperatures can activate the innate immune system and induce inflammation."
This is partly due to the heat-making toxins that leak from the intestines, leading to inflammation, he said.
The study involved recruiting participants during the summer months in Louisville, Kentucky, where temperatures are usually 29°C to 35°C, and analysing their blood for markers of inflammation and immune-system function.
“To estimate heat exposure, we used daily averages of ambient outdoor temperatures and the Universal Thermal Climate Index, a heat metric incorporating temperature, humidity, wind speed and ultraviolet radiation, designed to reflect a person’s thermal perception more accurately,” Dr Riggs said.
The analysis found for every 5ºC increase in UTCI, there was an increase in the levels of key markers of inflammation in the blood.
This indicates that relatively small changes in perceived temperature can significantly affect inflammation and immune-system markers.
The findings indicated that being exposed to the heat raises the number of some blood cells and a protein that leads to swelling and irritation in the body.
Higher temperatures were also linked to decreased levels of B-cells, crucial for producing antibodies to fight off infections.
“This suggests that exposure to high temperatures may impair our ability to fight off infectious agents,” Dr Riggs said.
Certain groups are more vulnerable to the adverse effects of heat.
“Older adults [over 65s] and people with cardiovascular disease are particularly at risk from the health effects of high heat,” Dr Riggs said.
This showed the need for protective measures, especially in hot climates such as the Middle East.
“The first heatwave of the summer is typically the most dangerous, as people have not had the opportunity to acclimatise to the higher temperatures," Dr Riggs said.
“Some practical strategies to minimise the harmful effects of heat exposure include increasing fluid intake, staying in cool or air-conditioned environments, wearing loose-fitting clothes and reducing activity levels."
As this study was published, the World Meteorological Organisation (WMO) issued a report highlighting record-breaking climate events in 2023.
Records were again broken, and in some cases smashed, for greenhouse gas levels, surface temperatures, ocean heat and acidification, sea-level rise, Antarctic sea ice cover and glacier retreat, the WMO said.
Heart attack risk
Another research published in Circulation reveals that extreme heat combined with fine particulate pollution (PM2.5) significantly increases the risk of fatal heart attacks, especially among women and older adults.
Analysing more than 202,000 fatal heart attacks in Jiangsu province, China, from 2015 to 2020, the study found the combination of extreme heat and high levels of PM2.5 to be particularly deadly.
Yuewei Liu, senior author of the study, emphasised the preventive angle.
“Our findings provide evidence that reducing exposure to both extreme temperatures and fine particulate pollution may be useful to prevent premature deaths from heart attack, especially for women and older adults,” Dr Yuewei said.
Both sets of research underline the critical importance of public awareness and action to mitigate the health risks associated with extreme temperatures and air pollution, and the need for adaptive strategies to protect vulnerable populations.
