According to research published on December 13, both extremely hot and cold temperatures increased the risk of death among people with cardiovascular diseases.

According to new research published on December 13 in the American Heart Association's flagship journal Circulation, both extremely hot and cold temperatures increased the risk of death among people with cardiovascular diseases, such as ischemic heart disease (heart problems brought on by narrowed heart arteries), stroke, heart failure, and arrhythmia.

Heart failure was the cardiovascular condition studied in this study that was most closely associated with the extra mortality brought on by extremely hot and cold conditions.

"The decline in cardiovascular death rates since the 1960s is a huge public health success story as cardiologists identified and addressed individual risk factors such as tobacco, physical inactivity, Type 2 diabetes, high blood pressure and others.

The current challenge now is the environment and what climate change might hold for us," said Barrak Alahmad, M.D., M.P.H., PhD, research fellow at the Harvard T.H. Chan School of Public Health at Harvard University in Boston and a faculty member at the College of Public Health at Kuwait University in Kuwait City.

Researchers explored how extreme temperatures may affect heart diseases - the leading cause of death globally. They analysed health data for more than 32 million cardiovascular deaths that occurred in 567 cities in 27 countries on 5 continents between 1979 and 2019.

The global data came from the Multi-Country Multi-City (MCC) Collaborative Research Network, a consortium of epidemiologists, biostatisticians and climate scientists studying the health impacts of climate and related environmental stressors on death rates.

Climate change is associated with substantial swings in extreme hot and cold temperatures, so the researchers examined both in the current study. For this analysis, researchers compared cardiovascular deaths on the hottest and the coldest 2.5% of days for each city with cardiovascular deaths on the days that had an optimal temperature (the temperature associated with the least rates of deaths) in the same city.

For every 1,000 cardiovascular deaths, the researchers found that:
1. Extreme hot days accounted for 2.2 additional deaths.
2. Extreme cold days accounted for 9.1 additional deaths.
3. Of the types of heart diseases, the greatest number of additional deaths was found for people with heart failure (2.6 additional deaths on extremely hot days and 12.8 on extremely cold days).

"One in every 100 cardiovascular deaths may be attributed to extreme temperature days, and temperature effects were more pronounced when looking at heart failure deaths," said Haitham Khraishah, M.D., co-author of the study and a cardiovascular disease fellow at the University of Maryland School of Medicine and the University of Maryland Medical Center in Baltimore.

"While we do not know the reason, this may be explained by the progressive nature of heart failure as a disease, rendering patients susceptible to temperature effects. This is an important finding since one out of four people with heart failure are readmitted to the hospital within 30 days of discharge, and only 20 per cent of patients with heart failure survive 10 years after diagnosis."

Researchers suggest targeted warning systems and advice for vulnerable people may be needed to prevent cardiovascular deaths during temperature extremes.

"We need to be on top of emerging environmental exposures. I call upon professional cardiology organisations to commission guidelines and scientific statements on the intersection of extreme temperatures and cardiovascular health. In such statements, we may provide more direction to health care professionals, as well as identify clinical data gaps and future priorities for research," Alahmad said.

The underrepresentation of data from South Asia, the Middle East and Africa limits the ability to apply these findings to make global estimates about the impact of extreme temperatures on cardiovascular deaths.

"This study contributes important information to the ongoing societal discussions regarding the relationship between climate and human health. More work is needed to better define these relationships in a world facing climate changes across the globe in the years ahead, especially as to how those environmental changes might impact the world's leading cause of death and disability, heart disease," said AHA Past President Robert A. Harrington, M.D., FAHA, who is the Arthur L. Bloomfield Professor of Medicine and chair of the department of medicine at Stanford University.