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.”

 
 
 
 

So why is Peterborough growing so quickly?

Peterborough Cathedral. Image: Jules & Jenny/Flickr/creative commons.

The latest instalment of our series, in which we use the Centre for Cities’ data tools to crunch some of the numbers on Britain’s cities.  

The 2001 census put the population of Peterborough at 156,000. Some time before next spring, it’s projected to pass 200,000. That, for those keeping score, is an increase of about 28 per cent. Whether this makes it the fastest growing city in Britain or merely the second or the fourth – the vagueness of Britain’s boundaries means that different reports reach different conclusions – doesn’t really matter. This is a staggering rate of growth.

Oh, and since austerity kicked in, the city council has had its grant from central government cut by 80 percent.

Expansion on this scale and at this rate is the sort of thing that’d have a lot of councils in our NIMBY-ish political culture breaking out in hives; that seems to go double for Tory-run ones in Leave-voting areas. This lot, though, seem to be thriving on it. “I think the opportunity in Peterborough is fantastic,” says Dave Anderson, the city’s interim planning director. “We’re looking at growing to 235,000 by the mid-2030s.”

More striking still is that the Conservative council leader John Holdich agrees. “I’m a believer in ‘WIMBY’: what in my back yard?” he says. He’s responsible, he says, not just to his electorate, but “to our future kids, and grandkids” too – plus, at that rate of growth, a lot of incomers, too.

All this raises two questions. Why is Peterborough growing so quickly? And what can it do to prepare itself?

If you’re a little uncertain exactly where Peterborough is, don’t worry, you’re in good company. Until 1889, the “Soke of Peterborough” was an unlikely east-ward extrusion from Northamptonshire, far to its south west. Then it was a county in its own right; then part of the now-defunct Huntingdonshire. Today it’s in Cambridgeshire, with which it shares a metro mayor, the Conservative James Palmer. When I ask Holdich, who’s giving me a whistlestop tour of the city’s cathedral quarter, to explain all this, he just shrugs. “They keep moving us about.”

Sitting on the edge of the Fens, Peterborough is, officially, a part of the East of England region; but it’s just up the road from East Midlands cities including Leicester and Nottingham. I’d mentally pigeonholed it as a London-commuter town, albeit a far flung one; but when I actually looked it up, I was surprised to discover it was closer to Birmingham (70 miles) than London (75), and halfway up to Hull (81).


The more flattering interpretation of all this is that it’s on a bit of a crossroads: between capital and north, East Anglia and the Midlands. On the road network, that’s literally true – it’s where the A1 meets the A47, the main east-west road at this latitude – and railway lines extend in all directions, too.

All of which makes Peterborough a pretty nifty place to be if you’re, say, a large logistics firm.

This has clearly contributed to the city’s growth. “It has access to lots of land and cheaper labour than anywhere else in the Greater South East,” says Paul Swinney, director of policy at the Centre for Cities. “Those attributes appeal to land hungry, low-skilled business as opposed to higher-skilled more knowledge-based ones.”

That alone would point to a similar economy to a lot of northern cities – but there’s another thing driving Peterborough’s development. Despite being 70 miles from the capital, the East Coast Main Line means it’s well under an hour away by train.

In 1967, what’s more, the ancient cathedral city was designated a new town, to house London’s overspill population. The development corporation which owned the land and built the new town upon it, evolved into a development agency; today the same role is played by bodies like Opportunity Peterborough and the Peterborough Investment Partnership.

The city also offers relatively cheap housing: you can get a four-bed family home for not much over £200,000. That’s fuelled growth further as London-based workers scratch around for the increasingly tiny pool of places that are both commutable and affordable.

The housing affordability ratio shows average house prices as a multiple of average incomes. Peterborough is notably more affordable than Cambridge, London and the national average. Image: Centre for Cities data tool.

It’s made it attractive to service businesses, too. “London has probably played quite a big role in the city’s development,” says Swinney. “If you don’t want to move too far out, it’s probably one of the cheapest places to move to.”

The result of all this is that it has an unusually mixed economy. There’s light industry and logistics, in the office and warehouse parks that line the dual-carriageways (“parkways”) of the city. But there are also financial services and digital media companies moving in, bringing better paying jobs. In a country where most city economies are built on either high value services or land-hungry warehousing businesses, Peterborough has somehow managed to create a mixed economy.

Peterborough’s industrial profile: more services and less manufacturing, and more private and fewer public sector jobs, than the national average. Image: Centre for Cities.

At the moment, if people think of Peterborough at all, they’re likely to imagine a large town, rather than the fair-size regional city it’s on course to become. Its glorious 12th century cathedral – the hallmark of an ancient city, and at 44m still by far the highest spot on the horizon for miles around – is stunning. But it’s barely known to outsiders, and at least twice on my tour, the council’s communications officer proudly announces that the Telegraph named her patch as one of the best towns to live in within an hour of London, before adding, “even though we’re a city”. 

So part of the council’s current mission is to ensure that Peterborough has all the amenities people would expect from a settlement on this scale. “What the city needs to do is to adopt the mind-set of a slightly larger city,” says Anderson. Slightly smaller Swansea is developing a new music arena, of the sort Peterborough doesn’t have and needs. He frets, too, about retail spend “leaking” to Cambridge or Leicester. “Retail is now seen as a leisure activity: in the core of the city it’s important that offer is there.”

To that end, the early 1980s Queensgate shopping centre is being redeveloped, with John Lewis giving up a chunk of space to provide a new city centre cinema. (At present, the area only has road-side suburban multiplexes.) There’s major office, retail and housing development underway at North Westgate, as well as work to improve the walking route between the station and the commercial centre, in a similar manner to Coventry.

Fletton Quays. Image: Peterborough Investment Partnership.

Then there’s the city’s underused riverside. The council recently moved to new digs, in Fletton Quays, on the far bank of the River Nene from the centre. Across the river from the Embankment, the city centre’s largest green space, it’s a pretty lovely spot, of the sort where one might expect riverside pubs or restaurants with outdoor seating – but at the moment the space is largely empty. The Fletton Quays development will change all that, bringing more retail space and yes, new homes, too.

Jobs in Peterborough are unusually distributed around town: in many cities, most jobs are in the central business district. Image: Centre for Cities.

The big thing everyone agrees is missing, though, is a university. It already has the University Centre Peterborough, where degrees are provided by Anglia Ruskin University. The plan is for the site – a joint venture between ARU and Peterborough Regional College – to go its own way as an independent institution, the University of Peterborough, in autumn 2022. That should help provide the skills that the city needs to grow. A growing student population should also bring life and cash to the city centre. 

How big could Peterborough get? Could its enviable combination of good location and cheap housing and grand ambitions combine to make it the modern equivalent of Manchester or Liverpool – one of the great cities of the 21st century?

Well, probably not: “I think the optimum size for a city is probably about 250,000,” says Holdich. But that’s still a whole quarter bigger than now, and the council leader even discusses the possibility of refitting his dual-carriageway-based-city with some kind of light rail network to service that growing population. Peterborough’s not done growing yet.

Jonn Elledge is the editor of CityMetric. He is on Twitter as @jonnelledge and on Facebook as JonnElledgeWrites.

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