Heart disease – The global analysis of more than 32 million cardiovascular deaths over 40 years measured higher fatalities when temperatures were highest or lowest compared to days with more moderate weather.
The second half of the 20th century witnessed the prevention of cardiovascular diseases, mainly by addressing traditional CVD risk factors such as tobacco use, hypertension, hyperlipidemia, diet, and physical activity. Despite this, CVDs remain the leading cause of death worldwide, claiming 18 million lives each year.
Climate change has caused extreme environmental temperature changes and an increase in mortality and introduced non-optimal temperatures among the main mortality risk factors worldwide. A recent global analysis showed that 9.4% of all deaths could be attributed to non-optimal high and low temperatures.
Dr. Barrak Alahmad, a researcher at the Harvard TH Chan School of Public Health at Harvard University in Boston (USA), led a study that carried out an analysis of deaths due to extreme temperatures and their relationship with heart disease, with databases of more than from 35 institutions around the world. The Multi-City Multi-Country Collaborative Research Network (MCC) is a consortium of epidemiologists, biostatisticians, and climate scientists who study the health impacts of climate and related environmental stressors on mortality rates.
Among types of cardiovascular disease, people with heart failure were the most likely to suffer the negative impact of frigid and sweltering days, experiencing a 12 percent increased risk of dying on days of extreme heat compared with those days of optimal temperature in a specific city. The extreme cold increased the risk of death from heart failure by 37%.
The findings were based on an analysis of health data from more than 32 million cardiovascular deaths in 567 cities in 27 countries on 5 continents between 1979 and 2019. The definition of extreme weather differed from city to city. It was defined as the top 1% or bottom 1 percent of the “minimum temperature of mortality.”
For every 1,000 cardiovascular deaths, the researchers found that days of extreme heat (above 86°F (30°C) in Baltimore) accounted for 2.2 additional deaths.
Frigid days accounted for 9.1 additional deaths.
Of the types of heart disease, the highest number of deaths occurred in people with heart failure (2.6 additional deaths on days of extreme heat and 12.8 on days of extreme cold).
Some limitations of the study include the underrepresentation of data from South Asia, the Middle East, and Africa. It could be that extreme heat had a more significant impact than initially measured due to this lack of data.
The researchers considered humidity and air pollutants, which could have explained the excess deaths in places with extreme temperatures. They also controlled for the lagged effect of temperature on human health (lagged effect) and climate zone.