Whether it is a day on the lake or an afternoon working in the yard, exposure to high temperatures may harm your health by impacting your immune system, according to University of Louisville research.

Periods of extreme heat often result in an increase in deaths, mostly related to heart conditions. A UofL research study shows that heat also can impair the immune system and increase damaging inflammation, according to Daniel Riggs, assistant professor of environmental medicine and affiliated with UofL’s Christina Lee Brown Envirome Institute.

Riggs and his colleagues recorded levels of immune cells and biomarkers in the blood of 624 participants in Louisville during summer months. They then compared those levels with the Universal Thermal Climate Index for that day, which factors in air temperature, relative humidity, wind speed and ultraviolet radiation levels as a measure of heat exposure.

They found that when it was hotter, the participants had higher levels of immune molecules in their blood, indicating a general immune response and inflammation, as well as lower levels of B-cells, which allow the body to fight specific infections. This means that with higher heat, people may be more susceptible to infection and more sensitive to environmental exposures, which in turn can contribute to worsened heart disease.

“We know that certain changes in the immune system and increased inflammation are a leading mechanism in many types of cardiovascular disease. Our findings suggest that heat exposure could be contributing to these processes that ultimately lead to greater risk of cardiovascular disease,” Riggs said.

Riggs presented the research at the American Heart Association Epidemiology, Prevention, Lifestyle and Cardiometabolic Health Conference in March.