What is pollution really doing to your brain?

The cocktail of chemicals in the air could be affecting everything from dementia to our children’s health, says Harry de Quetteville

Ihave a little gadget on my kitchen shelf. It measures levels of a particle known as PM2.5 – the tiny, invisible, sooty bits of combustion that are key culprits in the air pollution health crisis. Produced by diesel and petrol fumes, log burners and even conventional ovens, PM2.5S are small enough to make it deep into the lungs and from there into the bloodstream. They’ve been linked to diseases ranging from cancer to high blood pressure and, as the World Health Organisation (WHO) puts it, “increased mortality or morbidity”.

When I pop two slices of bread into the toaster for my four- and six-year-old, the monitor goes bananas. The PM count in micrograms per cubic metre races up from 9 or 10 into the hundreds. Meanwhile, the route to their primary school is one big busy road, and one of London’s network of pollution monitors is nearby. It testifies to a depressing reality that of the 79 months my elder son has been alive, the air in his home city has been “safe” to breathe, on average, for six.

The physical risks to him and his brother are well known, and worrying enough. Studies show such pollution is linked in adults to heart and lung disease, heart attacks and strokes. Children suffer reduced lung development and the development of chronic respiratory diseases.

But what about our brains? Increasingly, researchers are studying pollution’s effects on mental health, cognitive development and decline too – on attention spans and educational attainment in the young, on productivity in adults, and on diseases like Alzheimer’s in the old. Their findings are not reassuring.

Last month, for example, came the results of a large study carried out in Barcelona, involving more than 2,200 children aged between 7 and 10. Its conclusions were stark: “Early life exposure to PM2.5 was associated with a reduction in fundamental cognitive abilities, including working memory and [attention]”. Boys, it said, showed “much higher vulnerability”.

Last year, a study tracking 131,000 patients, aged 50 to 79, in London found that, even with other factors like smoking and diabetes taken into account, those in the most polluted areas were 40 per cent more likely to be diagnosed with dementia than those in the least polluted. Another significant study last summer, this time in China, quantified the effects of pollution on verbal and arithmetical reasoning as equivalent to “a few years of education”. “As people age, the negative effect becomes more pronounced, especially for men,” the study noted.

And these are just three in an increasingly significant body of studies. In 2017, a huge analysis of more than 2 million people found another correlation between pollution and dementia in London, stating that 7 per cent of dementia cases could be attributed to “elevated pollution exposure”.

Way back in 2008, Mexican researchers found that young adults exposed to long-term pollution (of the kind for which Mexico City is notorious) caused the brain to trigger an immune response resulting in inflammation of the nervous tissue.

At all stages of life, then – infant, adult and elderly – studies are finding serious impacts on brain function caused by pollution.

“There’s so much data on air pollution, on working memory and your capacity to think,” says Prof Barbara Demeneix, who runs a research lab in France’s National Scientific Research Centre (CNRS) and is author of Toxic Cocktail, How Chemical Pollution is Poisoning

Our Brains. She warns against complacency among those living outside cities. “It’s not just traffic. All volatile compounds, like pesticides found in rural areas, can be included.”

It is unclear precisely how the cocktail of chemicals in PM2.5 particles, in combination with other pollutants like nitrogen and sulphur dioxides, is impacting brain function. “Little is known about the possible mechanisms,” says Prof Frank

Kelly, an expert at King’s College

London, “other than pollution in general leads to increased systemic

inflammation, which damages (among others) the blood vessels supplying the brain.”

Prof Demeneix suggests that volatile chemicals attack the hormone-producing endocrine system, disrupting normal physical development. She worries, however, that the difficulty in pinning down precisely how the brain is damaged will be used as an excuse to do nothing.

Such findings have not just medical, but ethical implications. As Iain Carey, lead author in the London study, notes: “There may be a geographical pattern specific to dementia, and potentially Alzheimer’s.” Lifestyle and genes all play their part, he acknowledges. But what if your longterm brain health is also a factor of where you live? Ahead of Clean Air Day this week, politicians are jostling to display their commitment to improving air quality. Matt Hancock, the Health Secretary, described pollution as a “slow and deadly poison”. In January, Michael Gove, the Environment Secretary, launched the Government’s clean air strategy, admitting that air pollution “continues to shorten lives, harm our children and reduce quality of life”. He, Jeremy Hunt and Rory Stewart have all promised legally binding air-quality targets should they become the next prime minister.

With two million people in London living with illegal levels of pollution, achieving cleaner air within our lifetimes seems a monumental task. But there are already signs of progress, with the latest data showing nitrogen dioxide levels are falling. Even small reductions can have positive effects. In a study published last year by America’s National Bureau of Economic Research, US counties that took steps to improve their air quality saw an estimated 140,000 fewer dementia cases, and saved an associated $163 billion. When it came to exposure over a decade, reducing PM2.5 particles by just one microgram per cubic metre lowered the probability of a dementia diagnosis by more than one percentage point. Back in south-east London, my boys have spent their first decade often contending with pollution of more than 20 micrograms per cubic metre. It’s hard not to wonder if one day they may have to pay a terrible price.

Studies show links to lung disease, strokes and low attention spans