Extreme heat exposure may impair immune response, increase inflammation
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Key takeaways:
- Exposure to hot weather may trigger an immune response leading to increased inflammation.
- The association was significant even after adjusting for sociodemographic and behavioral risk factors.
Researchers in Kentucky identified mechanisms by which heat exposure caused immune response that may increase inflammation.
The data were presented at the Epidemiology, Prevention, Lifestyle & Cardiometabolic Scientific Sessions.
“It’s important for physicians to communicate with patients about the risk of adverse health effects from heat exposure,” Daniel W. Riggs, PhD, assistant professor of medicine in the Christina Lee Brown Envirome Institute at the University of Louisville, said in a press release. “For example, cardiologists could conduct customized consultations and assessments to increase patient awareness about their susceptibility to the effects of high temperatures. Also, changes to treatment regimens may be important to consider to address other risks. For example, some medications could make people more susceptible to heat-related illness or some may not be as effective when the body is exposed to high temperatures.”
To assess the relationship between short-term heat exposure and markers of inflammation, Riggs and colleagues gathered circulating cytokine and immune cell data from 624 participants from a neighborhood in Louisville, Kentucky (mean age, 50 years; 59% women; 77% white). Measures of heat exposure were calculated on the day of participants’ clinical visit during the summers of 2018 and 2019.
The median daily temperature when participants’ blood was drawn was 24.5°C (interquartile range [IQR], 3.8°C).
After adjusting for sociodemographic and behavioral risk factors, the mean daily Universal Thermal Climate Index (UTCI) was associated with elevated total circulating monocytes (4.2% per IQR; 95% CI, 0.3-8.3) and classical monocytes (CD14+ and CD16) and lower nonclassical monocytes (CD14 and CD16+), according to the presentation.
Riggs and colleagues also observed elevated eosinophils (9.5% per IQR; 95% CI, 0.6-19.1) and natural killer T cells (9.9% per IQR; 95% CI, 2.8-17.5) and reduced B cells (6.8% per IQR; 95% CI, 12.1 to 1.1) on days with elevated mean UTCI.
Analysis of circulating cytokines showed that increased UTCI was associated with elevated levels of tumor necrosis factor-alpha (7% per IQR; 95% CI, 2.8-11.4), interleukin-5 and macrophage inflammatory protein-1 alpha.
Other measures of heat exposure such as temperature and net effective temperature showed similar but attenuated effects on circulating cytokines and immune cells, according to the presentation.
“Our study participants only had minor exposure to high temperatures on the day of their blood test; however, even minor exposure may contribute to changes in immune markers,” Riggs said in the release. “With rising global temperatures, the association between heat exposure and a temporarily weakened response from the immune system is a concern because temperature and humidity are known to be important environmental drivers of infectious, airborne disease transmission. Thus, during the hottest days of summer, people may be at higher risk of heat exposure, [and] they may also be more vulnerable to disease or inflammation.”
Reference:
- Heat exposure may increase inflammation and impair the immune system. https://newsroom.heart.org/news/heat-exposure-may-increase-inflammation-and-impair-the-immune-system. Published March 19, 2024. Accessed March 19, 2024.
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Riggs DW, et al. Abstract P297. Presented at: Epidemiology, Prevention, Lifestyle & Cardiometabolic Scientific Sessions; March 18-21, 2024; Chicago.
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