What are the health risks and how to protect against them?

During extreme heat or heat waves, the body is put to the test. From the first rises in mercury, the body tries to keep its central temperature stable, around 37°C, like a thermostat. When the outside temperature approaches 40°C, as has been the case in several regions of France since Tuesday and most certainly until the very end of the weekend of June 18-19, the risk that the body will is growing. In populations at risk of course, but also in healthy people.

> DIRECT. Find all the news on the heat wave

On the occasion of this early heat wave, favored by global warming caused by human activity, franceinfo is looking at the health consequences of the increase in such a rise in temperatures.

Risks for (almost) everyone

To regulate its own heat, the human body puts in place mechanisms that require not only energy but also great adaptability. Thus, 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 the elderly, the number of sweat glands – whose role is to produce sweat, used by the body to cool off – decreases with age, leading to a rise in body temperature. They are also less sensitive to thirst, while infants can quickly suffer from dehydration.

But in addition to these physical vulnerability criteria, there is a risk linked to circumstances, activity, and even social status: “People who work outdoors or those who work or live in buildings with poor thermal insulation, present a greater risk of suffering more or less serious consequences from a heat wave. All the more so if these people are isolated”explains Alicia Pillot, general practitioner in Isère and member of the France Environmental Health Association. “Hence the importance of being attentive to fragile and/or isolated people around us and, if one is concerned oneself, 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, noting that “if the over 75 age group is the most affected, the 15-44 and 65-74 age groups are also affected.” Also in 2019, “12 fatal work accidents possibly linked to heat were notified by the Medical Labor Inspectorate, including five that occurred during heat waves”continues the agency.

In total, between 2014 and 2019, Public Health France has attributed 5,700 deaths in mainland France to heat waves, but also counts 5,200 emergency visits for heatstroke, including 1,500 children, and 5,900 emergency visits for dehydration, including 3,500 elderly people.

A wide variety of risks

heat stroke, “It’s the one we fear the most”, explains Alicia Pillot. “It is an overrun of the body’s temperature regulation 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 manifests itself mainly “in the form of heat exhaustion, with nausea, headache, dizziness, fatigue”, she lists. Therefore, if these symptoms occur, “You really have to refresh yourself, rehydrate yourself and warn those around you, ask for help if necessary, like consulting your doctor. Because with symptoms of this type, it can deteriorate quite quickly in fragile people.”

In its most serious form, which mainly affects frail people, “we have a fever over 40°C, serious neurological disorders, such as hallucinations, seizures, or coma”continues Alicia Pillot.

Including in the general population, cardiovascular risks increase in periods of high heat, she explains, citing strokes and thromboembolic disease, such as phlebitis and pulmonary embolism. “Due to dehydration, water loss, the blood will be more concentrated and more easily form clots in the blood vessels”she explains.

And for those who suffer from chronic illnesses, the heat exposes them to “a decompensation”. Cardiovascular diseases, kidney problems, diabetes, but also neurological and psychiatric diseases,… “All are much more at risk of becoming complicated or of experiencing acute events during a heat wave”, warns Alicia Pillot. In case of dehydration, the kidneys also clink, exposing to an increased risk of renal colic.

Risks that can always increase

“Heat episodes create enormous stress on the body,” explains Alicia Pillot. Gold, “the more the episodes are repeated, the closer they are or the longer they last, the more we risk exhausting the functions of the body”, she summarizes. Stress of the body, but also of the mind. “There are more decompensations of psychiatric illnesses with unsuitable behaviors, or suicide attempts and more risks of aggressiveness, especially among people who are already fragile”, notes the nurse.

It also points to the crisis in the hospital system and the pressure exerted by a heat wave on services which have been warning of their difficulties for several months, fearing that they will not be able to carry out their missions properly during the summer. Under these conditions, Alicia Pillot insists: “Prevention and solidarity is essential, because it is always better not to arrive at a situation that requires significant care.”

Finally, global warming and the future it holds for the younger generations worry the GP. The temperature has 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”she warns.

Risks that combine with others

In addition, heat waves are often accompanied by episodes of pollution in urban areas. We then have “more risk of an asthma attack or decompensation of chronic respiratory diseases, such as chronic bronchitis. On heat peaks that accumulate and worsen, there is also a greater risk of allergic symptoms which can be extremely embarrassing , such as rhinitis and conjunctivitis.”

But risks that can be limited

You have to stay hydrated and stay cool. Health authorities recommend avoiding going out at the hottest hours, keeping the accommodation cool 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 feel thirsty and cool off. “You simply have to get wet. Even over your clothes, with an atomizer, or with water. Do it several times a day without drying yourself off, it’s really effective”, ensures Alicia Pillot. “It does not make you forget to eat either. If you have trouble, you can favor foods rich in water: fresh fruits and vegetables, cold soups, compotes… Eat more often even if it means eating less large quantities.”

“For babies who are breastfed, we don’t necessarily need to offer them water, but we do offer them feedings on demand. On the other hand, it is absolutely essential that breastfeeding mothers drink a lot of water and are resting’, continues the general practitioner. “For bottle-fed children, we recommend offering water between milk bottles, which we continue to give at the usual rate.”

Finally, she advises to regularly give news to relatives, to seek help if necessary – in particular from the town hall for isolated people – and to keep informed – on the vigilance site of Météo-France or by calling the free heatwave info-service on 0800 06 66 66 -.