Recently, an analysis of DNA markers in more than 3,000 people published at the annual scientific meeting of the Gerontological Society of America (GSA) showed that long-term exposure to high temperatures is associated with molecular changes that may reflect accelerated aging.
High temperatures are known to stress the heart and kidneys and slow cognitive performance. But extreme heat can also have effects that are not initially visible. "This physical burden may not immediately manifest as observable health problems, but affects our bodies at the cellular and molecular level. This biological decline may develop into disability." said Eun Young Choi, a geriatrician at the University of Southern California in Los Angeles, and the author of the paper.
To find a sensitive measure of the impact of high temperatures on the human body, Choi and colleagues chose to study the "epigenetic clock," a set of DNA chemical modifications that change as humans age. Although there is debate over how well these measures represent aging, previous research has linked changes in these markers to environmental and social stress, pregnancy, and certain health conditions.
The researchers analyzed marker data from about 3,800 people aged 56 and older from 2016 to 2017. They cross-referenced the data with temperature maps of the United States, looking for correlations between molecular marker status and the number of days the heat index (a measure of perceived temperature and humidity) in the participants' locations exceeded 26.7°C or 32.2°C over different time periods. In addition, the researchers took into account factors such as racial and ethnic identity, smoking status, geographic location and income. It was found that, based on molecular markers, those who lived in areas with more hot weather "appeared older" than those who lived in cooler areas.
According to one metric, for every 10% increase in the proportion of hot weather, the molecular age of participants increased by about 0.12 years. Analysis of another set of molecular markers showed that people who lived in high-temperature areas for a long time accelerated their aging by 0.6%. However, short-term heat exposure, measured in days or months, was not associated with changes in these markers.
"This is a remarkable finding." Rina So, an environmental epidemiologist at the University of Copenhagen in Denmark, points out that this study is unique in that it focused on biomarkers in the blood rather than death or disease, and assessed the effects of both long-term and short-term exposure.
The study did not consider whether participants had air conditioning or assess how much time they spent outdoors. In addition, the study was not able to track individual specific responses to heat—a next step Choi hopes to conduct after obtaining molecular marker analysis data from blood samples collected in 2022.
Even so, researchers have struggled to determine whether high temperatures directly cause accelerated aging or whether other factors play a role. Linda Enroth, who studies public health and gerontology at the University of Tampere in Finland, said it is important to explore these potential links. "This is a brand new research method and idea that we urgently need," she said. "It is very important to understand how high temperature affects us."