According to research conducted in China on large population samples, air pollution causes a "huge" reduction in intelligence. The findings reveal that the damage caused to society by toxic air is much more profound than the well-known impacts on physical health.
Cand your research, published in the review Proceedings of the National Academy of Scienceswas conducted in China, but it is relevant worldwide. As a reminder, 95 % of the world's population breathes unhealthy air. Everyone is therefore concerned.
The main conclusion of this large study is to show that high levels of pollution led to significant decreases in language and arithmetic test scores, with an average impact equivalent to the loss of one year of a person's education.
" Polluted air can cause everyone to reduce their level of education by a year, which is huge. " Katie Bays, co-founder of the consulting firm Sandhill Strategy, said Xi Chen from the Yale School of Public Health in the United States, member of the research team. « But we know that the effect is worse for older people, especially those over 64, and for men, and for those with low levels of education. If we calculate [the loss] for these people, it could be a few years of education.... ".
To complete their study, researchers tested a sample of 20,000 people across the country for language and numeracy. The tests took place over four years, from 2010 to 2014. The scientists then compared the test results with records of nitrogen dioxide and sulfur dioxide pollution.
They found that the longer people were exposed to polluted air, the greater the damage to intelligence; linguistic ability was more affected than mathematical ability and men were more impacted than women. The researchers believe that this difference may be the result of the way male and female brains function.
For Dr. Derrick Ho of Hong Kong Polytechnic University, the impact of air pollution on cognition is well established. According to him, heavy air pollution can lead to oxidative stress, neuroinflammation and neurodegeneration. The observed correlation between pollution levels and loss of cognitive abilities is not linked, according to researchers, to genetic differences between individuals or to a normal gradual decline over time. The researchers corrected for these biases in their study and concluded that air pollution has a direct impact on the cognitive abilities of individuals.
A global public health issue
For them, this is a real public health issue. « There's no shortcut to solving this problem.says Dr. Chen. Governments really need to take real action to reduce air pollution. This can benefit human capital, which is one of the main drivers of economic growth. ». In China, air pollution is declining but remains three times higher than the World Health Organization (WHO) limits.
The issue of air pollution affects the entire planet. More than nine out of ten people on the planet breathe polluted air. This was the conclusion of the annual report on the state of the world's air published last April by the American Health Effects Institute (HEI). Prolonged exposure to this polluted air has led to more than six million deaths in 2016 alone, all over the planet.
According to the Chinese researchers who conducted the study, the damage to intelligence is likely to be incremental: an increase in pollution of 1 mg over three years would be equivalent to the loss of more than a month of education. Fine particles of pollution are known to be particularly damaging in this respect. According to a study conducted by Santé Publique France in June 2017, in the year 2016 alone, no less than 48,000 deaths were caused by fine particles in France, i.e. 9% of the national mortality. British researchers from the University of Lancaster had found toxic nanoparticles linked to air pollution "in abundant quantities" in brain tissue. They believe this discovery is directly related to the development of Alzheimer's disease, which affects tens of millions of people worldwide.
The new study that links air pollution to impaired intelligence and cognitive function adds to the disturbing body of evidence on the toxicity of polluted air. Everyone knows the causes of air pollution. In all countries, it is linked to car traffic, the combustion of fossil fuels and uncontrolled industrialisation. Current policies are not up to the challenge. The air pollution levels admitted by the WHO are exceeded in most developing countries and flirt with limits in many Western states. France is no better off than other regions of the world: according to the WHO, the level of fine particles in the air should not exceed 10 micrograms per cubic meter of air, yet in our country, it has not managed to drop below the 12 mg mark for the past fifteen years.