Heat is one of the main risks that the environment poses to our health. The scorching summer of 2022, for example, killed over 61 thousand people across Europe, and our country is the one that set the record for victims: more than 18 thousand deaths attributable to the heat. It's the fault of heat waves, which are increasingly common also due to global warming, and the slowness with which our society is able to adapt to climate changes. Knowing who is most at risk on days of intense heat is therefore essential, to allow prevention efforts to be concentrated where they are most needed. And that's what a group of Spanish and French researchers did in a study published in the journal Environmental Health Perspectivesanalyzing the most common causes of hospitalization on days of intense heat in Spain between 2006 and 2019. Here are the results.
The research was carried out using data collected by the healthcare system in 48 Spanish provinces. A country with problems similar to those of Italy, which in 2022 was the second for heat-related deaths in Europe, with over 12 thousand victims. By cross-referencing hospitalizations with average daily temperatures, humidity values and atmospheric pollutants (such as particulate matter, ozone and nitrogen dioxide), researchers from the Barcelona Institute for Global Health and the Institut national de la santé et de la recherche médicale ( Inserm) have calculated the impact of days of intense heat and heat waves on hospitalizations for various specific causes.
Confirming, first of all, the dangers, especially for young children and the elderly: the risk of hospitalization was in fact higher on hot days for all age groups, with a peak however in children under one year of age and in those over 85. Sex was also found to be a determining factor: for men, in fact, days of intense heat mainly increase the risk of hospitalization due to accidents, while for women the greatest increase emerged due to parasitosis, endocrine, metabolic and respiratory diseases. and urinary.
“The mechanism by which heat triggers adverse health events is not yet completely clear, but it seems to have to do with the way the body regulates its temperature,” explains Hicham Achebak, an Inserm researcher who participated in the study. “In conditions of thermal stress, the body activates cutaneous vasodilation and sweat production to disperse heat. The resulting reactions can affect people differently based on a number of factors, such as age, gender, and the presence of pre-existing health problems. We know, for example, that the threshold beyond which sweat production is activated in women is higher, and that they are more susceptible to the effects of heat.”
The group of pathologies that caused hospitalizations on hot days in the study period was that of metabolic pathologies and obesity, with a number of hospitalizations on hot days double compared to the norm. Subsequently, the risk was also very high for renal failure, urinary tract infections, sepsis, urinary tract stones, poisoning from drugs and other substances.
Humidity, however, was not particularly decisive with respect to the risks of hospitalization, with a small increase relating to bronchitis and bronchiolitis in particularly dry periods. The same goes for air pollution, which the study linked only to hospitalizations for metabolic disorders, obesity, and diabetes. That's not all: even the effects of heat waves appear to be much smaller than those of individual days of extreme heat.
“We observed that the cumulative effects of heat waves – extreme temperatures that last for several consecutive days – are small, and specific to a precise subset of diseases, primarily non-respiratory infectious diseases, endocrine and metabolic disorders, and nervous system diseases,” concludes Joan Ballester Claramunt, of the Barcelona Institute for Global Health. “For this reason, we think that early warning systems for extreme heat should not only be activated during heat waves, but also in the presence of non-persistent extreme temperatures.”