what are the health risks of heat (and how to prevent them)?

If you live in France, the temperature may put your body to the test in the coming days. A particularly early heat wave, favored by global warming caused by human activity, has been sweeping the territory since Wednesday June 15 and should last until the weekend. Météo France placed 23 departments on orange “heat wave” vigilance on Wednesday.

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From the first rises in mercury, the body seeks to maintain a stable core temperature, around 37°C, like a thermostat. When the outside heat approaches 40°C, as is already the case in several regions of France, the risk of the body racing increases. In the most fragile populations of course, but also in healthy people. Franceinfo looks in detail at the health consequences of such a rise in temperatures.

The most vulnerable are not the only ones concerned

To regulate its own heat, the human body puts in place mechanisms that require not only energy, but also great adaptability. This is the reason why the elderly or affected by chronic pathologies, children, infants or even pregnant women are among the most vulnerable people in the face of these events.

In older people, the number of sweat glands – which produce sweat – decreases with age, affecting the body’s ability to cool off. Our elders are also less sensitive to the feeling of thirst and therefore may not realize that they are short of water. As for infants, they dehydrate more quickly because water represents 80% of their body mass at birth, compared to 60% in adults.

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In addition to these criteria of physical vulnerability, there are risks linked to circumstances, activity and even social status. “People who work outdoors, or those who work or live in buildings with poor thermal insulation, are at greater risk of suffering the consequences of a heat wave. Even more so if they are insulated”explains Alicia Pillot, general practitioner in Isère and member of the Association Santé Environnement France. “Hence the importance of being attentive to fragile and/or isolated people around us. And, if you are concerned yourself, to ask for help.”

Because heat kills, and not just old people. In its annual bulletin published at the end of the summer of 2019 – during which two extensive and intense heat waves hit France –, Public Health France establishes a link between excess mortality and high heat. The organization notes that, “if the over 75 age group is the most affected, the 15-44 and 65-74 age groups are also affected.” This year, “12 fatal work accidents possibly linked to heat were notified by the medical labor inspectorate, including five that occurred during heat waves”continues the report.

In total, between 2014 and 2019, Public Health France attributed 5,700 deaths to heat waves in metropolitan France. To which are added 5,200 emergency visits for heatstroke, including 1,500 children, and 5,900 for dehydration, including 3,500 elderly people.

Heat promotes a wide variety of pathologies

The heat stroke “is the one we fear the most”, explains Alicia Pillot. “It is an overrun of the body’s temperature-regulating capacities, which involves dehydration – with the loss of water and mineral salts through perspiration – and an excessive increase in temperature.“, explains the general practitioner.

It mainly manifests “in the form of heat exhaustion, with nausea, headache, dizziness, fatigue”, she lists. If these symptoms occur, “You really have to cool off, rehydrate and ask for help if necessary, warn those around you or consult your doctor. Because symptoms of this type can deteriorate quite quickly in fragile people.” In the most severe form of heat stroke, which mainly affects the most vulnerable, “we have a fever over 40°C and serious neurological disorders, such as hallucinations, seizures or coma”warns Alicia Pillot.

Cardiovascular risks also increase in periods of high heat, including in the general population, explains the doctor. She cites, for example, strokes and thromboembolic diseases, such as phlebitis and pulmonary embolism. “Because of dehydration, the blood will be more concentrated and will more easily form clots”she explains.

Finally, the heat exposes those who suffer from a chronic illness to “a decompensation”. Cardiovascular diseases, kidney problems, diabetes, neurological and psychiatric diseases… “All are much more at risk of becoming complicated or of experiencing acute events”, warns Alicia Pillot. Dehydration also affects the kidneys, which increases the risk of renal colic.

Environmental factors aggravate the risks

“Heat episodes create enormous stress on the body,” explains Alicia Pillot. Gold, “the more the episodes are repeated, closer together or last longer, the greater the risk of exhausting the functions of the body”, she summarizes. Stress of the body, but also of the mind. “We observe more decompensation of psychiatric illnesses or suicide attempts, and more risk of aggressiveness, especially in people who are already fragile”, notes the nurse.

In addition, the heat is often accompanied by episodes of pollution in urban areas. Residents are at increased risk “asthma attack or decompensation of chronic respiratory diseases, such as bronchitis”, warns Alicia Pillot. More extreme temperatures “pile up and get worse”the more they are accompanied “allergic symptoms that can be extremely bothersome, such as rhinitis and conjunctivitis.”

Heat waves also pose collective challenges. The consequences of the heat wave on health risk increasing the pressure on the hospital system, where caregivers have been warning about their difficulties for several months, in particular in the emergency room. In this context, “prevention and solidarity are essential”insists the general practitioner, for “not to arrive at a situation which requires important care.”

Finally, global warming and the future it holds for the younger generations worry Alicia Pillot. The average temperature has already increased by 1.1°C compared to the pre-industrial era. Given the delay in ecological transition policies, scientific models place us “on a trajectory of +2.5°C or +3°C by 2100”, she fears. “At this stage, the effects of the heat waves will be beyond measure”.

Advice can help protect yourself

Two principles are essential: stay hydrated and stay cool. Health authorities recommend avoiding going out at the hottest hours, lowering the temperature of your home as much as possible, or spending several hours a day in a cool place (cinema, municipal library, supermarket, museum, etc.) .

It is also recommended to drink water regularly, without waiting to be thirsty, and to cool off. “You just have to get wet”, summarizes Alicia Pillot. “Even over clothes. Doing it several times a day without drying out is really effective”. “Don’t forget to eat more”warns the general practitioner. “If you have trouble, you can favor foods rich in water: fresh fruits and vegetables, cold soups, compotes… And eat more often, even if it means eating smaller quantities.”

For parents of infants, it is necessary to be attentive to the symptoms of dehydration: weight loss, drowsiness or apathy, dry mucous membranes, sunken or dark circles in the eyes, sunken fontanelles or even the fact that the baby urinate less than usual. “For bottle-fed children, we recommend offering water between milk bottles, which we continue to give at the usual”, details Alicia Pillot. Those who are breastfed do not need extra water if “we offer them feedings on demand”. On the other hand, she advises breastfeeding mothers to “drink plenty of water and rest”.

Finally, the doctor advises to regularly give news to relatives, and to seek help if necessary – especially from the town hall for isolated people. In case of questions or if symptoms occur, the free Heatwave info service telephone line is available on 0800 06 66 66.