Experimental research in environmentally induced hyperthermic older persons: A systematic quantitative literature review mapping the available evidence

ABSTRACT

The heat-related health burden is expected to persist and worsen in the coming years due to an aging global population and climate change. Defining the breadth and depth of our understanding of age-related changes in thermoregulation can identify underlying causes and strategies to protect vulnerable individuals from heat. We conducted the first systematic quantitative literature review to provide context to the historical experimental research of healthy older adults – compared to younger adults or unhealthy age matched cases – during exogenous heat strain, focusing on factors that influence thermoregulatory function (e.g. co-morbidities). We identified 4,455 articles, with 147 meeting eligibility criteria. Most studies were conducted in the US (39%), Canada (29%), or Japan (12%), with 71% of the 3,411 participants being male. About 71% of the studies compared younger and older adults, while 34% compared two groups of older adults with and without factors influencing thermoregulation. Key factors included age combined with another factor (23%), underlying biological mechanisms (18%), age independently (15%), influencing health conditions (15%), adaptation potential (12%), environmental conditions (9%), and therapeutic/pharmacological interventions (7%). Our results suggest that controlled experimental research should focus on the age-related changes in thermoregulation in the very old, females, those with overlooked chronic heat-sensitive health conditions (e.g. pulmonary, renal, mental disorders), the impact of multimorbidity, prolonged and cumulative effects of extreme heat, evidence-based policy of control measures (e.g. personal cooling strategies), pharmaceutical interactions, and interventions stimulating protective physiological adaptation. These controlled studies will inform the directions and use of limited resources in ecologically valid fieldwork studies.

KEYWORDS:

• Aging
• chronic disease
• climate change
• heat exposure
• heat strain
• heat stress
• heatwaves

Disclosure statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Data availability statement

All associated data and the R code generated for analysis is available upon request.

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/23328940.2023.2242062.

Correction Statement

This article has been corrected with minor changes. These changes do not impact the academic content of the article.

Additional information

Funding

This research was funded in whole by the Wellcome Trust [224709/Z/21/Z: ‘Individualised heat-health early warning systems: A novel digital solution’].

Notes on contributors

Aaron J. E. Bach

Aaron J. E. Bach Dr. Aaron Bach is a thermal physiologist and research fellow in the School of Medicine at Griffith University (Australia). The focus of Aaron’s research is the impact of heat on vulnerable populations. This includes quantifying health impacts of heat in the workplace with steps toward mitigating occupational heat strain, and protecting older persons from extreme heat events by leveraging technology that provides real-time, personalised advice on sustainable cooling strategies. Dr Bach hopes his research provides tangible solutions to heat-induced health risks, striking a balance between scientific rigor and practical applicability.

Sarah J. K. Cunningham

Sarah J. K. Cunningham Sarah Cunningham holds a Bachelor’s degree in Applied Science, with a focus on Microbiology, from the Queensland University of Technology. She further education by pursuing a Diploma in Science, specialising in Biology, as well as a Graduate Diploma in Epidemiology from the University of Queensland. Building on her passion for public health, she earned a Master’s degree in Public Health from Griffith University. Sarah is presently working towards a Doctor of Medicine degree at the University of Queensland, reflecting her commitment to broadening her medical knowledge and expertise.

Norman R. Morris

Norman R. Morris Norman Morris is a physiotherapist who holds a joint research position as Professor (Cardiothoracic) at The Prince Charles Hospital, Brisbane and Griffith University on the Gold Coast. His program of research examines the factors that limit, and interventions that improve, exercise tolerance in individuals with chronic heart and lung disease and is undertaken in both clinical and laboratory-based settings.

Zhiwei Xu

Zhiwei Xu Dr. Zhiwei Xu is a mid-career researcher at the School of Medicine and Dentistry. His primary research interest is to identify and quantify the health impacts of climate change (particularly extreme heat) and develop accessible and sustainable adaptation strategies. As of July 2023, he has a Google Scholar H-index of 38 and has been cited 5,300 times, including citations in 54 policy documents from the United Nations, WHO, World Bank, European Union, and governments of Australia, Brazil, Finland, Germany, Nepal, and USA.

Shannon Rutherford

Shannon Rutherford Associate Professor Rutherford is a public health specialist with research career focussed on the links between environmental change and human health. With attention to building capacity to understand, assess and respond to the consequences at the local, national and global level. Her research spans climate and health in diverse settings - from heat and health adaptation policy in India and worker health in Bangladesh garment factory workers. She leads several transdisciplinary research teams. These include projects aimed to reduce the health impacts of heat on older populations, the Queensland Heat-Health Community of Practice and the Citizen Science for Cool Schools project.

Sebastian Binnewies

Sebastian Binnewies Dr. Sebastian Binnewies serves as a Senior Lecturer in the School of Information and Communication Technology at Griffith University and is the incumbent Director of the Griffith App Factory. He has numerous publications in top-tier academic forums and has a track record of successfully securing substantial external grant funding. Dr. Binnewies has a wide range of research interests that include data science, text analytics, and knowledge representation & reasoning, with a dedication to multidisciplinary approaches in technology and data interpretation.

Robert D. Meade

Robert D. Meade Dr. Robert D. Meade is a Postdoctoral Fellow at the Human and Environmental Physiology Research Unit and a recent recipient of a Masters in Public Health from the Harvard T.H. Chan School of Public Health. His research is directed at understanding the physiological impacts of heatwaves and evaluating the effectiveness of commonly recommended heat-mitigation strategies in older adults with and without common age-associated chronic health conditions (e.g., type 2 diabetes, hypertension). He is also interested in the design of translational physiological research for complimenting public health research and practice.