As the sentinel of human health, the World Health Organization (WHO) rarely brings good news. She did not deviate from the rule, Thursday February 1: the UN institution anticipates an increase of some 35 million new cases of cancer by 2050. Or 77% more than in 2022, said the agency of the Organization specializing in this disease.

Among the key factors in the increase in incidence incriminated by the study, air pollution.

Fine particles, then a cellular bug

“This is mainly about fine particle pollution,” specifies Dr Emmanuel Ricard, spokesperson for the League Against Cancer.

Diesel exhaust is one of the main sources of these particles, he continues: the finest of them can go down the tree of the lung, to the alveoli, these small "bags" where exchanges gases between the lung and the blood, oxygenating the latter.

Our defense cells will “want” to remove these particles. Inflammation follows. This ends up disrupting the cells which, instead of continuing to replicate in a healthy way, will start to “bug”, becoming cancerous. “Respecting nothing, these cancer cells multiply and form a tumor,” the doctor popularizes.

More numerous, older, more sick

Clearly indicated by the study, at least two factors in this increase in cases have no link with pollution. Demographic, the first factor is only a simple arithmetic bias: as the number of human beings continues to increase, the total number of cancer cases also increases.

More numerous, our species is also aging. “But cancer is a problem of immunity, and the older we get, the more immunity declines. Result: the longer the population has a life expectancy, the more it will be subject to cancer.”

Another classic sham of any epidemiological data: the best case diagnosis. Cases that already existed in the past, but simply escaped medical radar, are now being detected, causing the numbers to increase.

Worse, for epidemiologist Catherine Hill, we observe situations of “overdiagnosis”, where we confuse the presence of cancer cells with cancer strictly speaking.

A textbook case in this area is prostate cancer: according to the Health Surveillance Institute (INVS), 30% of 30-year-old men and 80% of 80-year-old men have cancer cells in their prostate. “It is extremely common: it is therefore obvious that not all of these cancer cells give rise to symptomatic cancers,” explains this specialist in the frequency and causes of cancer.

Pollution and bad habits

More and more studies are establishing – often in the conditional – a link between pollution and the deterioration of our health, including mental health. Depressing: pollution even aggravates depression.

Also read: Increase in cases of autism: a study puts pollution in the dock

“A fashion” full of scientific approximations, annoys Catherine Hill. After tobacco, alcohol consumption is the leading cause of cancer in France according to the WHO, recalls the epidemiologist. “Pollution causes 50 times less cancer in France than tobacco and 20 times less than alcohol,” she emphasizes, citing a study by the WHO International Cancer Research Center.

But it would be wrong to perceive the factors of cancer as isolated, nuance the spokesperson for the League against Cancer. Faced with several factors, we are not witnessing a simple addition, but rather a multiplication of risk. The knowledge we have on the impact of the tobacco-alcohol alliance is demonstrated elsewhere, he continues: “We were thus able to find, in lung cancer, genes as much impacted by cigarettes as by atmospheric pollution” .

The “South”, this “dumping ground” of the world

But this pollution factor is not the same for everyone, because we do not all breathe the same air. "In the big cities of China, India, South America, Tananarive [in Madagascar, Editor's note], or even Cairo, the pollution is such that clouds of particles form. Under this 'smog', people develop lung cancer, exactly like in England during the industrial revolution,” notes Emmanuel Ricard.

There is now a transfer of pollution towards a "South", used as the "dumping ground of the world", continues Emmanuel Ricard: "In addition to the 'risky' factories that industrialized countries prefer to relocate, we sell derivatives to developing economies low-cost, but lower-quality oil tankers.

Those who have visited the megacities of these countries will agree: the pollution there seems more “pungent”. This is because it is indeed more aggressive, explains Emmanuel Ricard: “The diesels used are even richer in sulfur and nitrogen than those released in Europe”.

For him, the WHO report thus highlights an epidemiological transition: countries which were mainly impacted by infectious diseases – which have declined – will face the multiplication of diseases that were found more in Western countries, like cancers.

Ecological click?

Among the latter, France, where air quality has improved over the past thirty years. In the Toulouse metropolitan area, for example, fine particles and nitrogen oxide fell by 40% and 17% respectively between 2009 and 2019. The positive impact on cardiovascular diseases, strokes, heart attacks and cancers is demonstrated, notes Emmanuel Ricard.

Less encouraging: the study carried out in the Toulouse region also concludes that the economically disadvantaged population is more exposed to air pollution and affected by deaths attributable to long-term exposure.

Beyond these socio-economic disparities, Xavier Briffault, researcher in social sciences and philosophy of health at the CNRS, sees an ecological trigger: by demonstrating a direct correlation between health and environmental degradation, science would take us from an ethical ecology to a public health ecology.

Especially since health is not just an end in the ecological fight, but also a means, adds the researcher: mobilizing our fears, the health issue allows us to put pressure on politicians according to this argument, "Not only do you kill the planet but you are killing us".

“Polluting is bad” would thus fall into disuse: we would realize that polluting “does harm”.

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