How is rising air pollution affecting our brains?

Children in New Delhi protesting air pollution in 2017. Image: Getty.

Breathing in dirty air has been conclusively linked to both heart and lung problems, and the consensus is that pollution is, to say the least, bad for us. Around 7m people die from exposure to fine particles in polluted air every years. These particles enter the lungs and cardiovascular system, causing heart disease, lung cancer, respiratory infections and strokes.

But new research has suggested dirty air may also be affecting our brains – impacting our cognitive function and intelligence.

Last month, a study carried out by researchers at the Yale School of Health and Beijing University suggested that chronic exposure to air pollution could be linked to cognitive performance. The results of the study, which involved testing the maths and verbal skills of around 20,000 people in China, showed that high levels of air pollution lead to significantly lower test scores. For those exposed the longest, the drop was equivalent to a loss of a whole year of schooling.

A separate study, published in September, suggested air pollution may increase the chance of developing dementia. The data, collected in London, suggested people aged over 50 in areas with the highest levels of nitrogen oxide in the air had a 40 per cent greater risk of developing dementia than those with the least pollution.

And last year, a UNICEF study warned that 17m babies across the world are breathing in toxic air, which was putting their brain development at risk. It suggested that ultrafine pollution particles are small enough to enter the bloodstream, travel to the brain, and damage the blood-brain barrier.

Children are more vulnerable because they breathe more rapidly, the study suggested, but also because their physical defences and immunities are not fully developed.

The gaps in the data

It’s not all that surprising that air pollution may affect our health in multiple ways. The problem is that researchers still don’t know exactly how – or why – It impacts our brains.

Professor Pamela J Lein, of the department of molecular biosciences at the University of California, Davis, suggests the brain may become damaged due to inflammation.

 “The experimental evidence indicates that air pollution can impact the structure of at least the developing brain. And in both the developing and aged brain, air pollution can trigger a neuroinflammatory response,” she says.

“Neuroinflammation is important to protect the brain – but if it is sustained too long, it can become injurious and interfere with communication between neurons in a neural circuit, and eventually may become neurotoxic and cause neuronal cell death.”

Neuronal cell death is thought to be the cause of cognitive decline in many neurodegenerative diseases such as Alzheimer’s disease, Lein explains. “But even persistent interference with how neurons communicate with each other can be sufficient to manifest as cognitive decline,” she adds.

Although we’re beginning to hypothesise about how air pollution might impact the brain, we still don’t know which air pollutants are to blame.

There are lots of pollutants which can cause health risks, including particulate matter (or PM – a mix of solid and liquid particles suspended in the air), ozone, nitrogen dioxide and sulphur dioxide. The smallest particles are the most damaging because they can get farthest into the lungs.


The research for the Chinese study was based on measurements of sulphur dioxide, nitrogen dioxide and particulates smaller than 10 micrometres in diameter, but not carbon monoxide, ozone and larger particulates. Yet it’s not clear which of these pollutants is responsible for the study participants’ cognitive decline.

More research is need to understand exactly how pollutants enter the brain, too.

“I could spin a good narrative yarn, says Dr Ian Mudway, a lecturer in respiratory toxicology at King’s College London. “I could tell you that we breathe particles, and particles travel up the olfactory nerves to the brain, and those particles are rich in metals, and we know that metals seem to be involved in the acceleration of the injury patterns associated with dementia

“I could say all of those things – but if Iwas being completely honest and transparent, I'd have to, at each of those stages, say, ‘But we don't really know how valid those statements are’.

“As with all fields, very often there's a tendency to suggest that everything is much clearer than it really is.”

It’s also not yet possible to pinpoint whether air pollution directly impacts brain function, because there are so many different factors involved.

Living near roads with heavy traffic has been associated with an increased incidence of alzheimer’s disease, Lein highlighted in an op-ed published earlier this year with her colleague Anthony Wexler – but this association poses a number of questions.

For example, is the effect because of the higher concentration of air pollutants? Or is it because housing is less expensive near busy roadways, so people with lower incomes and possibly poorer diets live near these roads?

Epidemiologic studies may find a correlation between air pollution and neurodegenerative disease – but this doesn’t mean pollution is the cause.

Much more research is needed to show how strong the link is between air pollution and brain function, and exactly what is causing this link.

What we do know, though, is that many of the risk factors for cardiovascular disease are the same as the risk factors for dementia – and we have already established that air pollution has a detrimental impact on the heart. “If you look at the risk factors for stroke, for example, hypertension, these are risk factors for dementia, so maybe it's not a tremendous surprise,” Mudway says.

“We are at this very early point in this field – a bit like air pollution was with cardiovascular disease back in the mid-90s,” he explains. “People had found associations, but there were still considerable uncertainties about how we understood this.

“All the pieces are scattered on the table, and you can see what the picture is – but the pieces don't quite fit yet.”

 
 
 
 

In New Zealand, climate change is driving an eco-nationalist revival

The green and pleasant land of the South Island. Image: Getty.

“Ten years ago I would have called them settler f*****g land squatters,” Mike Smith, Maori-dom’s most tenacious activist, said last November as he reflected on the agriculture industry’s central role in driving climate change. “Now I have to try and get these people on board.”

Smith is infamous for taking a chainsaw to Auckland’s most prominent tree on a damp October night in 1994 in protest of the “Pākehā” – or white European –dominated government’s fiscal envelope restraining treaty settlements. Now he’s turned his hand to another cause close-to-home for the Maori, New Zealand’s indigenous population: the environment.

“We’re super vulnerable, like we are to anything,” Smith says. “When it comes to climate change it’s like the poorest people in the world are going to be hit the hardest first, and that’s a lot of us.”

Prime Minister Jacinda Ardern appears, at least rhetorically, the most sympathetic leader to his cause in a decade. In her campaign launch speech late last year, she made the future government’s position clear: “Climate change is my generation’s nuclear free moment.”

This message should resonate with followers of her Labour party: the NZ left has long nurtured an environment-orientated “culture-of-protest”. So Ardern’s call to arms was bound to gain her loyal support among children of the 1960s and ‘70s, who led the march against nuclear ship visits, spurring on the government of the time to wriggle out from the US nuclear umbrella, and place a ban on foreign nuclear ship visits.

Now, it is to the tycoons of deep sea oil exploration they aim to close NZ’s ports.

In this, Smith is not short of support locally, with marches run by grassroots organisations and international animal welfare funds beginning to gain traction with every day New Zealanders. In this, Ardern’s prediction is correct: the Coal Action Network Aotearoa (CANA), is reminiscent of the Campaign for Nuclear Disarmament (CND), an earlier cluster of left-wing pacifists and nature lovers who drove the creation of the nuclear free zone.  

In December, 15,000 passionate protesters marched through the capital. And with the government’s recent ban of offshore oil exploration projects, Jeanette Fitzsimons, former Green party co-leader and the head of CANA, is optimistic about similar change to the energy and farming sectors.

The Labour-NZ First-Green party coalition seems focused on setting a new global precedent, weaning NZ away from a United States which has jettisoned the Paris Agreement. The move replicates another 20 years ago, when New Zealand’s anti-nuclear movement was central to an upsurge in New Zealand nationalism. Now, the same sense of going it alone on foreign policy is apparent both locally and in Parliament.

Dr. Gradon Diprose, a senior lecturer at Massey University, argues that this echoes an older expression of colonial nationalism, that saw “New Zealand as a land of natural abundance”. This: “eco-nationalism” is centered on “protecting certain visions of picturesque landscapes and unspoiled natural beauty”. The slogan “Clean, green New Zealand” is prevalent in popular culture and tourism marketing. The public seems to have latched onto it too, and ranked keeping NZ’s waterways “clean and green” top of a recent survey of of kiwis’ top concerns.

Three decades ago, it was the 10 July 1985 sinking of the Greenpeace flagship Rainbow Warrior that thrust local activists’ fears into the public eye, resulting in an almost nation-wide expression of climate-protectionism.


The bombing, a French intelligence operation sparked by Greenpeace’s calls for an end to foreign nuclear testing in the Pacific, galvanised a great deal of change to New Zealand’s overseas defence policies. A lack of censure from New Zealand’s Western allies drove Wellington to distance itself from the United States, while the shock of seeing a friendly nation violate NZ’s sovereignty left many at home seething.

Thirty years on, the foreign policy split throughout the Anglosphere, regarding Russian-Western relations, globalism, and the old international rules-based order, is becoming wider. Climate change is just the tip of the iceberg.

Most Kiwis you talk to will shake their heads in disapproval at US president Donald Trump’s scandalous outing last year in Helsinki. But US defiance of internationally brokered climate resolutions is something they can see clearly reflected in rural communities across the country.

The country saw records broken at both ends of the extreme weather spectrum last year. As 2018 kicked off, Kiwis sweltered through the hottest summer on record, while in Golden Bay, a small inlet near the northern tip of the South Island, residents endured the largest flood in 150 years. So, when President Trump tweets “So much for Global Warming”, the majority of New Zealanders look back fondly on NZ’s 1985 decision to boycott the “ANZUS” treaty, putting New Zealand at odds with its war-time ally America on defence legislation.

Public calls to take the same track on environmental regulation have become louder in the wake of Donald Trump’s election. The former US Secretary of State, Rex Tillerson, received a frosty “unwelcome” while on a flyby to the capital in 2017, with the New York Times’ Washington correspondent, Gardiner Harris remarking: “I’ve never seen so many people flip the bird at an American motorcade as I saw today”. Protests against President Trump’s stance on climate change are beginning to gain greater traction further still, with the hundred-strong “march for science” setting the tone for the new government later that year.

New Zealand certainly isn’t afraid of radicalism, and its activists are persistent. It’s already banned single use plastics in supermarkets. Plenty more is to come, Smith says.

And yes, reform is going to inhibit sometimes vital industries: “It doesn’t matter which way you spin the dice on this, whatever’s being done is going to hurt. People who are looking for a painless way of mitigating climate change, [but] I don’t think there is one.”

But among Smith’s troupe of climate agitators, the feeling is that, without drastic change, “the land”, the heart of the Maori ethos, is going to be hurt far more.

Back in Auckland, NZ’s financial hub, an electric scooter craze is gripping the city. This, too, has gained the support of local environmentalists. In New Zealand, a national sense of pride is always coupled with a certain eccentricity. In a country this size, change always starts small.