It is no secret that sizzling in the sun for long periods is bad for your health.
As well as the headaches and risk of heatstroke, sunbathing dramatically increases the chance of skin cancer, with 70 percent of cases of the disease linked to sun exposure.
But now, researchers have added two further serious harms to the list: heart disease and a wrecked immune system.
Scientists from the University of Louisville in Kentucky found that just a day in a hot outdoor environment can raise tell-tale signs of inflammation in the body by at least 10 percent.
Some of these signs – the release of inflammatory compounds that lead to a spiral of internal damage – are explicitly linked to the build-up of plaque in the arteries, leading to heart disease.
Researchers from the University of Louisville in Kentucky studied 624 adults, who had their blood taken during the summer months between May 2018 and September 2019
The study also showed a six percent drop in crucial immune system cells called B-cells, which help the body fight viruses and germs.
For the study, 624 adults had their blood taken once during the summer months between May 2018 and September 2019.
The average temperature on the days participants visited the clinic for blood tests was 76 degrees Fahrenheit (24.5 degrees Celsius).
The researchers analyzed the blood tests for multiple markers to show how well the immune system was performing.
They were looking specifically at levels of key compounds released by the immune system when it detects injury, like T and B cells, as well as cytokines (signaling molecules that can trigger inflammation).
They then looked at links between the markers and heat levels, including temperature and net effective temperature – which takes into account humidity, the temperature of the air and the speed of the wind.
They also compared Universal Thermal Climate Index (UTCI), which factors in temperature, humidity, wind speed and ultraviolet radiation levels.
They found that for every five degree increase in UTCI, there was an increase in natural killer T-cells, which suggests inflammation had occurred in the body.
This difference, the researchers said, was the equivalent of going to a day out of the heat, to a day with moderate thermal stress.
There was a 10 percent increase in killer T-cells in participants’ blood, which activate the immune system and trigger an inflammatory response in the body to protect against pathogens and injury.
While inflammation is a normal part of the body’s defenses against infection, a consistent inflammatory response over time (lasting weeks to months), or that occurs in healthy tissues, is damaging and plays a key role in the build-up of plaque in the arteries.
This can lead to the development of coronary artery disease and heart attacks.
Researchers also found a seven percent decrease in B cells, which suggests a reduction in the part of the immune system which remembers specific viruses and creates antibodies to tackle them.
‘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,’ said lead study author Daniel Riggs, assistant professor of medicine at the University of Louisville.
Prof Riggs added that adults older than age 60 and adults with existing cardiovascular disease are particularly at risk for heat-related cardiovascular events and deaths.
‘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, they may also be more vulnerable to disease or inflammation.’
