According to a report by the WHO (World Health Organization) and the WMO (World Meteorological Organization), heat is one of the biggest health problems worldwide and kills around 15 million people per year.
In Europe alone, during the summer of last year there were more than 61 thousand deaths, according to a study carried out by scientists from a French health institute and ISGlobal (Barcelona Institute for Global Health), published in Nature Medicine.
Now, in Brazil, 15 states and the Federal District are under red alert (great danger) from Inmet (National Institute of Meteorology), due to the heat wave.
Cities like São Romão and Coronel Pacheco, in Minas Gerais, have already reached the mark of more than 40ºC. Rio de Janeiro reached 36.8ºC, but had a thermal sensation of 58.5ºC in Guaratiba, in the west of the city.
Even with this number, it is not common to see a high number of deaths, as occurs in Europe. Therefore, is it correct to say that Brazilians are more resistant to heat?
Yuri Silva, biologist and technical director at the Mapinguari Institute, explains that, first, it is necessary to understand that the two types of heat are different.
“In Brazil, the heat is more humid, because we have, despite being reduced and threatened, tropical forests: the Atlantic forest, the Amazon, the cerrado — as the cradle of waters —, the Pantanal. All of these ecosystems maintain high air humidity, which favors perspiration, sweat, which is a temperature control mechanism. This doesn’t happen in Europe, the heat there is drier”, he explains.
There is also the difference between the summer solstice, the time of year when the days get longer. In the Northern Hemisphere, it takes place in June, and the average sun exposure is 16 hours a day. For comparative purposes, in December, when it arrives in the Southern Hemisphere, exposure is around 12 hours.
“The day is longer and the night is shorter, so there is less time for the temperature of houses, and the city in general, to decrease. When it starts to decrease, it’s daytime again and a new exhibition is arriving”, says Silva.
Houses are also a problem, as in Europe they are built to retain heat. In the United Kingdom, for example, according to data from the Department for Business, Energy and Industrial Strategy, only 5% of homes have air conditioning, and the majority are portable.
The European population is also older, which makes adaptation even more difficult. According to the WHO, next year the number of people aged 65 on the continent will surpass that of young people under 15.
But what impacted the countries most was the sudden change in climatic conditions — the body is unable to respond and rebalance itself. Last year, in France and Italy, for example, the average temperature rose by 2.43°C and 2.28°C, respectively.
For all these points, it is correct to say that Brazilians are adapted to their own climatic conditions and have certain “advantages” compared to Europeans.
However, despite not dying, the most vulnerable populations in the country are already suffering from high temperatures, fires and heavy rains, for example.
But, after all, what is the limit?
In terms of heat, it is important to highlight that every species has an established limit. Human beings are homeothermic, that is, regardless of the external temperature, the internal temperature remains relatively constant: between 35.5°C and 36.5ºC.
Control is carried out through the central nervous and circulatory systems. The body’s heat sensors send signals to the hypothalamus, a region of the brain that triggers physiological control responses, such as increased sweating and accelerated breathing (exhalation of hot air).
When considering the external temperature, the limit for the body, according to the Wet Bulb Index — Globe Thermometer, is between 35ºC and 37ºC. From there, there is considerable discomfort, and the body’s thermoregulatory mechanism can become overloaded — it is important to emphasize that tolerance varies from person to person.
“Prolonged exposure to temperatures above 40ºC can lead to serious health problems”, warns Roberto Yano, cardiologist and specialist in artificial cardiac stimulation by the SBCCV (Brazilian Society of Cardiovascular Surgery) and AMB (Brazilian Medical Association).
This is why extreme heat is a warning. It is harmful to the human body, especially the circulatory system, for a number of reasons.
“The heart beats faster when it is very hot, to try to control the temperature and also due to dehydration. Because it beats faster, it uses more energy and more oxygen than it would need”, explains Hélio Castello, cardiologist and hemodynamics coordinator at the Specialized Cardiology Center at Hospital Alemão Oswaldo Cruz.
Arteries also dilate to balance body temperature. This dilation causes a drop in blood pressure.
“The third factor, which also affects the entire circulatory system, is that, when it is very hot, we become dehydrated. What carries the most water in our body is the blood, so once you lose water, theoretically, it would make the blood a little more concentrated, more viscous. This increases the risk of forming clots, which can clog a vessel”, says Castello.
And he adds: “Finally, in very extreme temperatures, inflammation of the entire circulatory and respiratory system often occurs.”
This means that anyone, except children, in extreme heat is at greater risk of having a heart attack (when a blood clot blocks blood flow to the heart) or stroke (when vessels carrying blood to the brain become clogged or ruptured).
“Dehydration and dilation of peripheral blood vessels can contribute to a decrease in cerebral blood flow, increasing the likelihood of cerebrovascular events,” explains Yano.
Overloading the heart also increases the risk of cardiac arrhythmia (irregular beats) and heart failure. This is because, in addition to the “double work” of the organ, the body loses electrolytes through sweat, such as sodium and potassium, which are essential for maintaining normal heart function.
Therefore, Castello recommends people to drink lots of water and be aware of faster than normal heartbeats in this heat, which could be a warning of dehydration. Elderly people and children, especially, become dehydrated more easily.
Yano adds that people should avoid alcoholic beverages, which increase dehydration, and pay attention to the signs of lack of water: dizziness, weakness, nausea and mental confusion.
