Study analyzes impact of summer heat on hospitalizations

A team from the Barcelona Institute for Global Health and the French National Institute of Health and Medical Research (Inserm) analyzed hospitalizations associated with high summer temperatures in Spain over more than a decade. The study concludes that the reasons for hospitalization most affected by heat include:

• Metabolic disorders and obesity.
• Kidney failure.
• Urinary tract infection.
• Sepsis.
• Uurolithiasis.
• Poisoning with medicinal and other non-medicinal substances.

The study, published in the journal Environmental Health Perspectives, included data from more than 11.2 million hospitalizations from 2006 to 2019. These data were limited to emergency hospitalizations from 48 provinces of mainland Spain and the Balearic Islands and were provided by the Spanish National Institute of Statistics.

The team also calculated average daily temperature, average daily relative humidity and concentrations of various air pollutants (PM2.5, PM10, NO2 and O3). Using various models, they assessed the relationships between temperature and various causes of hospitalization during the summer season (June to September) and by province.

As expected, the statistical analysis showed that high temperature had an "overall effect on cause-specific hospitalizations." Although heat increased the risk of hospitalization in all age groups, children under 1 year of age and adults over 85 years of age were the most vulnerable groups with a higher risk of hospitalization. Gender differences were also found, as on hotter days men had a higher risk of hospitalization due to injury than women, whereas women had a higher risk of hospitalization due to parasitic, endocrine and metabolic, respiratory or urinary diseases.

“The mechanisms by which heat causes adverse health effects remain unclear, but they appear to be related to the way our body regulates its own temperature,” says Hicham Achebak, researcher at INSERM and ISGlobal and fellowship holder Marie Skłodowska-Curie from the European Commission.

"Under conditions of heat stress, the body activates cutaneous vasodilation and sweating to lose heat. The subsequent responses may affect people differently depending on a number of factors, such as age, gender, or existing health conditions. We know, for example, that Women have a higher temperature threshold above which sweating mechanisms are activated and they are more susceptible to the effects of heat," he adds.

Obesity and metabolic disorders The group of diseases most affected by heat included metabolic disorders and obesity. The risk of hospitalization for these diseases on the hottest days was almost double compared to days of optimal or comfortable temperature.

"There are several reasons for this. For example, in obese people, heat loss processes work less efficiently because fat tissue acts as an insulator, making them more susceptible to heat disorders," says Hicham Achebak.

Relative Humidity, Air Pollution and Heat Waves Among the other variables included in the study, relative humidity did not play a significant role in the relationship between heat and emergency hospitalizations, except for the risk of acute bronchitis and bronchiolitis, which was higher on days with low relative humidity. Humidity.

In addition, days with high air pollution seemed to increase the risk of heat-related hospitalization for metabolic disorders and obesity, as well as diabetes, but not for other diseases.

"We observed that the additive effects of heat waves - or extremely high temperatures for several days in a row - 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 early warning systems for heat health should be activated not only during heat waves, but also during variable temperature extremes,” says Joan Ballester Claramunt, ISGlobal researcher and senior author of the study.