A recent study indicates that heat is the main factor associated with deaths from respiratory diseases in Brazil, surpassing the impact of cold, contradicting popular beliefs and previous research conducted in other countries.
Researchers from the State University of Campinas (Unicamp), by analyzing over one million death records in 646 Brazilian municipalities between 2010 and 2020, concluded that about 66 thousand deaths from respiratory problems were linked to temperatures outside the lower-risk range for the Brazilian population, established at 22.4 °C.
Of these cases, 4.27% were attributed to heat, while 1.81% were related to cold. Although heat is not considered the direct cause, high temperatures harm the respiratory system in several ways. Dehydration caused by heat dries out the airways, thickens pulmonary secretion, which hinders its elimination and intensifies irritation, favoring infections and crises of conditions such as asthma and COPD.
Pulmonologist Humberto Bogossian, from Einstein Israelite Hospital, explains that the need to breathe faster to try to dissipate heat overloads the respiratory system. He adds that other elements common during hot periods, such as low humidity, pollution, burning, and increased ozone, add to the risk. Bogossian also points out that the loss of green areas and the accumulation of impermeable surfaces in cities create heat islands that worsen the situation.
Guilherme Coelho, the first author of the research and family doctor, highlights that this predominance of heat diverges from decades of studies conducted in Europe and the United States, where cold is traditionally the climatic factor most linked to respiratory mortality. Coelho observes that Brazil has changed this scenario because, in about three-quarters of annual days, the country exceeds the comfort point of 22.4°C, causing the accumulation of deaths to be greater due to greater exposure to heat.
In terms of risk, days of intense heat increased the probability of death by 43%, compared to the 29% increase observed on days of extreme cold. Coelho warns that Brazil still has little preparation to deal with very high temperatures, both in terms of infrastructure and social adaptation.
In clinical practice, this change is already noticeable: respiratory exacerbations that were previously concentrated in autumn and winter are now distributed throughout the year. The pulmonologist reports an increase in respiratory exacerbations in spring and summer, mainly affecting COPD and asthma, while winters have become shorter and milder, and heat periods more intense.
The study also revealed significant regional disparities. While the North recorded the highest proportion of respiratory deaths linked to heat (approximately 12.5%), in the South, cold continues to be the dominant climatic factor in deaths. According to Guilherme Coelho, this demonstrates that a single prevention strategy does not suit the entire national territory. He points out that the lowest-risk point in the North is around 32°C, and in the South, it is approximately 23°C, indicating that uniform public policies are ineffective, requiring specific plans for heat in the North and Northeast, and cold-focused measures in the South.
The research raises the concept of the 'cold paradox', exemplified in Amazonian states, where temperatures close to 24°C, considered pleasant in much of the country, can locally increase the risk of respiratory death. Coelho explains that the core of the problem is not just the thermometer reading, but rather the deviation from the temperature to which the population is accustomed, as houses designed to dissipate heat and little physiological adaptation to the cold contribute to this phenomenon.
The elderly constitute the most vulnerable group, responsible for about 75% of respiratory deaths associated with temperature extremes. This occurs because aging decreases the body's ability to regulate temperature, predisposing to dehydration and often coexisting with chronic respiratory and cardiovascular diseases.
To mitigate risks during heatwaves, it is recommended to stay well hydrated, avoid sun exposure during peak hours, wear light clothing, humidify environments, keep respiratory treatments up to date, and ensure vaccination against influenza, Covid-19, pneumococcus, and respiratory syncytial virus (RSV).