Research examining how the immune system responds to hot weather has provided new insight into what’s happening when mercury levels rise.

Researchers found a link between hot weather and measures of the body’s immune response, including levels of certain blood cells and indicators of inflammation. This is a step toward ultimately finding treatments that can help protect people from dangerously high fevers, which are associated with increased rates of heart attacks, strokes, and other cardiovascular diseases.

The study, presented Tuesday at the American Heart Association’s Epidemiology, Prevention, Lifestyle, and Cardiometabolic Health Conference in Chicago, is considered preliminary until full results are published in a peer-reviewed journal. It is considered.

Lead researcher Dr. Daniel W. Riggs, an epidemiologist and assistant professor in the department of environmental medicine at the University of Louisville School of Medicine in Kentucky, said previous studies have linked body temperature and inflammation.

Inflammation, which is associated with heart disease risk, is part of the body’s response to infection or injury. Different types of white blood cells are also part of the immune response. Some of these cells release proteins called cytokines that regulate inflammation. Other immune cells directly attack invaders such as bacteria and viruses.

Cytokines and immune cells can be measured as markers of how well the body has mounted defenses in response to a perceived threat.

Riggs said previous research on heat and inflammation had only looked at a few signals that indicate how the body is responding. He and his colleagues “wanted to get a more complete picture of what the relationship between high temperatures and these markers is.”

The researchers examined blood samples taken from 624 participants in the Green Heart Project, which is studying how planting greenery in the Louisville area improves air quality and reduces heart disease.

Study participants ranged in age from 20 to 70 years, with an average age of 50 years. Approximately 77% were white, 18% were black, and 59% were female. Each person provided her one blood sample in the summer of 2018 and her 2019.

The researchers measured 11 types of cytokines and nine types of immune cells in each sample. Weather on each blood draw day was assessed using the Universal Thermoclimatic Index, a measure of how temperature, humidity, and wind speed affect the level of human comfort. The 24-hour average UTCI during measurements was 78 degrees Fahrenheit.

They then matched the blood measurements with weather measurements and adjusted the results for differences in demographic factors such as gender, age, race, and education. The results were also adjusted for body mass index (a measure of obesity), air pollution, and whether people smoked or took anti-inflammatory drugs.

The results showed a link between hot weather and increased levels of several cytokines. One of these, TNF-α, “is one of the major inflammatory markers and plays an important role in cardiovascular disease,” Riggs said.

At the same time, hot weather is associated with increased levels of some classes of white blood cells known as monocytes, which may be a sign that heat is causing inflammation or boosting the immune response. said Riggs.

Fever was also associated with decreased levels of another class of monocytes known as non-classical, which reduce inflammation. Fever was also associated with decreased levels of white blood cells known as B cells, which fight infections and cleanse the blood. Low levels of these cells could mean someone is more susceptible to infection, Riggs said.

He was amazed to see so many types of cells change when exposed to high temperatures for short periods of time. Although the study did not examine the cause, Riggs said acclimatization to heat may lead to an increase in heat shock proteins, which are known to be involved in immune and inflammatory responses. .

“I think this is an important study,” said Dr. Judith Lichtman, chair of the department of chronic disease epidemiology at the Yale School of Public Health in New Haven, Connecticut. She has conducted research on how temperature affects stroke speed but was not involved in the new study.

Much of the research so far has looked at whether heat waves lead to increased hospitalizations and deaths, she says. “What’s so valuable about this study is that we’re trying to understand at the physical level the mechanisms that may be contributing to this increased risk.”

The study only covered one region, so the findings need to be replicated more widely, she said. And such studies don’t reveal how much outdoor heat people actually are exposed to. People may be staying indoors with air conditioning.

But overall, the study “opens up a new field of research,” Lichtman said. As the climate changes, understanding the effects of heat on the body becomes increasingly important, and if researchers can begin to understand how aspects of the environment affect health, We may also be able to come up with new ways to reduce vascular risks.”

Riggs said climate change is expected to increase the number of heatwaves. “Our future research will focus on the long-term effects of exposure to extreme heat on immune responses and inflammation, and how this relates to the progression of cardiovascular disease. .”

As part of the Louisville Green Heart Project, Riggs said, “We’re going to look at whether actually planting trees can reduce the impact on the immune system and inflammation.” Other ongoing research includes collecting additional blood samples. “The main limitation of this study is that it is only one time point,” he said, adding that additional samples will show whether the findings persist.

“The more we understand the mechanisms, the more clearly we can address prevention and treatment,” he said.