A study analyses the impact of summer heat on hospital admissions in Spain
The study concludes that the causes of hospitalisation in which the heat has the most notable impact are: metabolic and obesity-related disorders, kidney failure, urinary tract infection, sepsis, urolithiasis.
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The research, published in Environmental Health Perspectives, included data from more than 11.2 million hospital admissions between 2006 and 2019. These data were restricted to admissions through emergency departments in 48 provinces in mainland Spain and the Balearic Islands and were provided by Spain's National Institute of Statistics. The team also calculated values for daily mean temperatures, daily mean relative humidity and concentrations of different air pollutants (PM2.5, PM10, NO2 and O3). With the help of different models, they estimated the relationships between temperature and the different causes of hospitalisation for the summer season (June to September) and by province.
As expected, the statistical analysis showed that high temperatures had "a widespread impact on cause-specific hospitalisations". Although heat increased the risk of hospitalisation in all age groups, children under 1 year and over 85 years were the most vulnerable groups, with the highest risk of hospital admission. Sex differences were also found, with men showing a higher risk of hospitalisation for injuries than women on the hottest days, while women had a higher risk of admission for parasitic, endocrine and metabolic, respiratory or urinary diseases.
"The underlying mechanisms by which heat triggers adverse health outcomes remain unclear, but appear to be related to the way our body regulates its own temperature," says Hicham Achebak, Inserm and ISGlobal researcher and holder of a Marie Sklodowska-Curie postdoctoral fellowship from the European Commission. "Under heat stress, the body activates cutaneous vasodilation and sweat production to lose heat. The subsequent reactions may affect people differently depending on a number of factors, such as age, gender or pre-existing health conditions. We know, for example, that women have a higher temperature threshold above which sweating mechanisms are activated and are more susceptible to the effects of heat," he adds.
Obesity and metabolic disorders
The group of diseases most affected by the heat were metabolic disorders and obesity. The risk of hospital admission for these diseases on the hottest days almost doubled compared to days of optimal or comfort temperature. "There are several reasons for this. For example, in people with obesity, heat loss responses work less effectively because body fat acts as an insulator, making them more susceptible to heat disorders," says Hicham Achebak.
Relative humidity, air pollution and heat waves
As for other variables included in the study, relative humidity did not appear to be relevant to heat with emergency hospital admissions, except for the risk of acute bronchitis and bronchiolitis, which was higher on days with lower relative humidity. In addition, high air pollution days appeared to exacerbate the risk of heat-related hospitalisation for metabolic disorders and obesity, as well as diabetes, but not for the other health outcomes.
"We observed that the added effects of heat waves - or extremely high temperatures for consecutive days - were small and specific to a subset of diseases, mainly non-respiratory infectious diseases, endocrine and metabolic disorders or diseases of the nervous system, among others. For this reason, we believe that current heat-health early warning systems should be activated not only during heat waves, but also during non-persistent extreme temperatures", says Joan Ballester Claramunt, ISGlobal researcher and last author of the study.
Reference
Hicham Achebak, Grégoire Rey, Zhao-Yue Chen, Simon J Lloyd, Marcos Quijal-Zamorano, Raúl Fernando Méndez-Turrubiates, Joan Ballester. Heat exposure and cause-specific hospital admissions in Spain: a nationwide cross-sectional study. Environmental Health Perspectives. 2024. https://doi.org/10.1289/EHP13254
About ISGlobal
The Barcelona Institute for Global Health (ISGlobal) is the result of an innovative alliance between the "la Caixa" Foundation and academic and governmental institutions to contribute to the efforts of the international community to address health challenges in a globalised world. ISGlobal consolidates a node of excellence based on research and medical care that has its origins in hospitals (Hospital Clínic and Parc de Salut MAR) and academia (University of Barcelona and Pompeu Fabra University). Its working model is based on the generation of scientific knowledge through Research Programmes and Groups, and its translation through the areas of Training and Analysis and Global Development. ISGlobal is accredited as a "Severo Ochoa Centre of Excellence" and is a member of the CERCA system of the Generalitat de Catalunya.