How bad air affects our health

But does this exposure to air pollution affect us, and what’s the evidence for harm? Well there are signals that asthma, heart disease, stroke, cognitive decline and even behavioural problems in young children are linked to poor air. So how big are the numbers? Gary Fuller looks at the epidemiology of air pollution at Imperial College London…

Gary - You've probably heard something about the 1952 smog and may even have seen it on an episode of The Crown. That taught us that really bad periods of air pollution killed people. A week-long smog in London in 1952 is thought to have killed around 12,000 people. Since then, we've learnt that the air pollution we experience on a daily basis actually causes more harm than these short-term spikes. One of the first studies in this area was done in the US and started in the 1970s. They followed the lives of people living in six cities for around 14 to 16 years. What they found looking across these cities was that people were dying at different rates in these cities. Some of it was explainable by things that we know about, like smoking, diet, weight, and things like this. But there was a large section that they couldn't explain, and that part we couldn't explain was associated with particle pollution in the air.

Chris - And what is the disease burden then, across the world, that we attribute to people breathing bad air day in, day out?

Gary - Globally, we estimate that over four million people are dying early because of the air pollution that they breathe. That's outdoor air pollution. Many people are cooking, for instance, in very confined spaces over open fires. And that's thought to add around two to three million to that score. It's estimated in London that around 4,000 people are dying early from air pollution that they breathe. For the UK, it's probably as many as 40,000. Europe, around 400,000. So these aren't small numbers and it's not just confined to developing countries. It's a global problem.

Chris - How do scientists think, though, that air pollution actually leads to this loss of life? Because when we say something causes something, if it's going to fulfill the criteria for causality, it's got to be biologically plausible. There's got to be a mechanism we can point at to say, this is how this is happening. What do we think, at a high level, is going on when people are exposed chronically to bad air, and why that translates into people dying?

Gary - One set of theories is that particle pollution - and other gaseous pollution that you have - just simply overcomes the natural defences that are present in our lung linings. And this, in turn, causes inflammation, which then affects the whole circulatory and respiratory system.

Other theories put forward suggest that smaller particles can actually transfer across the lung lining and enter our body, where they can then affect biological mechanisms.

I think one of the most interesting things that's emerging in the last probably 10 years is new knowledge that air pollution is also affecting our brain health. And here, one of the exposure routes may not be through the lungs and circulatory system, but may actually be through the olfactory bulb that sits there at the back of your nose and is more or less connected to your brain. It's suggested that some particle pollution may be able to enter the brain directly from that point.

Chris - I remember talking to the team down in London who got placentas collected from women who'd just recently given birth, living in London. They reported finding particulates, presumably breathed in by those women while they were pregnant, in those placentas. So this suggests that you begin to be affected by pollution before you've even been born in some cases.

Gary - That's right. The early studies and those that most of our legislation and regulation is based on is the science of the 20th century. Through the 21st century, we've been learning that air pollution affects us through all stages of our life, not just at the end of our life when we talk about someone's death being brought forward. There's evidence that air pollution is affecting pregnancy. We have outcomes such as miscarriage or babies being born with low birth weight for their gestational age. Through childhood, we of course know a lot about things that you may read about in the newspaper to do with new cases of asthma, for instance. And we see the same through adulthood. We're also seeing other disease endpoints such as cancer and stroke.

But I think most troubling really that's coming out new, as I say, is this new evidence on brain health. Within children that are exposed to air pollution, we're seeing behavioural things in the classroom to do with attention deficits and those sorts of learning things. And then later on in life, we're seeing firmer evidence of air pollution and depression and dementia as well.

Chris - A lot of the commentary around air pollution tends to be quite negative. But I suppose one of the good things about studying this, if we find these associations and causal relationships, is that then we have a way of intervening. Because we can say, well, if we know that is doing that, we can then do something about it. And we know what to measure to see if the intervention is actually working.

Gary - And there's quite a few studies that have been done that have shown exactly this. Perhaps one of the most famous ones was done in Ireland around 1990. And at that time, a lot of Irish homes in Dublin were burning coal for heat. The government banned the most smoky types of coal from sale. And that produced an instant improvement. So, in the following winter, the number of people that were dying from respiratory problems in Dublin reduced by 16%. And if you can think about that as one in eight, it's a big impact on the city.

But if we want to look to the future, one of the biggest things we're going to do this century is action on climate. Dr. Maria Neira from the World Health Organization was speaking in London just a couple of weeks ago. And she framed the action we're going to take on climate as possibly the biggest public health intervention of the century. For instance, in the US, it's estimated that by 2035, if they choose to follow actions on climate, they could reduce the number of people dying from air pollution by somewhere between 4,000 and 15,000 per year. And, importantly, saving the US economy between about $65 and $128 billion.