Study of more than 46m deaths globally reveals who is most at risk from non-optimum temperatures and which diseases are most affected

Monash University

The large international study of the health impacts of cold and heat has just been published in The Lancet’s eClinicalMedicine journal, finding that 4.4% of deaths between 2000 and 2019 can be attributed to short-term exposure to non-optimum temperatures across ten countries or territories.

The study is one of the most comprehensive multi-country analyses to examine how temperature-related mortality risks vary across different diseases, age groups, and sexes.

Led by Monash University researchers in Australia, the researchers analysed over 46 million deaths from nine causes across ten countries/territories revealing the demographics of those most affected and the diseases most likely to occur.

Dr Bo Wen and Professor Yuming Guo’s study identified three distinct exposure-response patterns:

• higher risks from cold than from heat for most causes;
• equivalent risks from cold and heat for respiratory mortality;
• higher risks from heat for injuries and external causes;
• the diseases most affected were mental health disorders (6.53%), nervous system diseases (6.40%) and cardiovascular conditions (5.71%)

Importantly, the research reveals the risks were not the same for everyone, according to Dr Wen. “We found that older adults were more vulnerable to cold-related nervous system diseases and neoplasms (cancers), while younger individuals were more affected by heat-related risks for injuries and external causes,” he said. “This study shows that public health strategies need to move beyond general warnings about heat or cold and instead focus on specific diseases and vulnerable groups.”

The study analyzed associations between temperature and mortality in 1117 locations from ten countries or territories (Australia, Brazil, Canada, Chile, Mexico, New Zealand, Philippines, South Korea, Taiwan, and Thailand) from 2000 to 2019.

Across the study period (approximately two decades, varying by country), the researchers estimated that 2·03 million deaths were attributable to non-optimum temperatures, corresponding to 4·38% of all deaths. For most causes of death, cold temperatures accounted for the largest proportion of mortality. However, for deaths related to infectious as well as injury and external causes, heat exposure contributed to the majority of the mortality.

According to Professor Guo, this is the largest multi-country study to date to characterise cause-, age-, and sex-specific mortality risks associated with non-optimum temperatures.

“Critically, differences in temperature-related mortality risks were observed between subgroups of age and sex,” Professor Guo said.

“With the impacts of cold and heat varying across causes of death.”

Read full paper Mortality risk due to non-optimum temperatures by cause of death, age, and sex: a multi-country time-series study in The Lancet’s eClinicalMedicine: https://www.doi.org/10.1016/j.eclinm.2026.103920

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