Air pollution: How strong is the link to cancer?

Fiona Osgun of Cancer Research UK explores whether a smog can cause serious illness

(Getty Images)

Air pollution’s role as a cause of cancer has slowly been shifting to the centre stage over the past few years. And news stories like Oxford Street’s nitrogen oxide levels being among the highest in the world, the Volkswagen emissions scandal and the law suit against the UK government for breaching pollution limits have all helped nudge it closer to the spotlight.

But thanks to another set of headlines this morning, we’re also seeing questions asked as to exactly what can be done to fix the problem.

A panel of experts from the Royal College of Physicians and the Royal College of Paediatrics and Child Health have published a report into the lifelong impact of air pollution

The report, called Every breath we take, looks at the effect of exposure to polluted air on the risk of a range of diseases – including asthma, heart disease, diabetes and cancer

It estimates that about 40,000 deaths each year in the UK are linked to air pollution, and suggests what the public and policymakers can do to minimise the risk.

But where did the figure come from? And how can it be brought down?

How strong is the link with cancer?

Over the past decades evidence that air pollution is linked to a range of cancers has been mounting. In 2013, a group of international experts, working on behalf of the World Health Organisation’s International Agency for Research on Cancer (IARC), looked at the results of all of the research and concluded that air pollution causes cancer in humans – in particular, lung cancer.

But what do these experts mean by ‘air pollution’? The term is very broad, and covers a host of ‘nasties’ including miniscule particles, tiny fragments of metals and gases. But when it comes to cancer risk, research so far shows that tiny dust-like particles just millionths of a metre wide – so called ‘particulate matter’, or PM – are the main culprit. In particular, the smallest particles – less than 2.5 millionths of a metre across, known as PM2.5 – appear to be behind lung cancers caused by pollution. These are chiefly found in emissions from diesel engines – something IARC have also ruled causes cancer in humans (we discuss this in more detail here).

In fact, about eight in every 100 cases of lung cancer each year in the UK are attributable to PM2.5 air pollution exposure – very roughly, that equates to about 3,500 people. By comparison, in 2013 (the most recent year for which good data are available), there were around 45,000 lung cancer cases diagnosed overall).

But as the report discusses, there’s a lot we still need to know about air pollution and our health.

More than the sum of its parts?

The authors of the report are experts in their fields, and by looking at all of the evidence they’ve mapped out where some of the uncertainty lies.

Importantly, no-one knows exactly how these microscopic particles damage DNA inside cells and cause cancer. Rather than directly damaging the cells themselves, it’s possible they’re the fall guy for another culprit – the particles are so small they can travel deep into the lungs, carrying other harmful chemicals such as polycyclic aromatic hydrocarbons (which are known to cause cancer) into the airways. Or perhaps it’s a combination of both that sets cells on the road to cancer. The report has called for more research into this.

Another area that needs further investigation is in understanding about how the mix of different pollutants might interact to cause health problems. Most research so far has focused on measuring one specific pollutant and looking for health effects – which isn’t how people are exposed to air pollution in real life.

The report goes on to say that, because of limitations like this in the research, they could even be underestimating the true health effects of air pollution.

Looking ahead, the report looks at what would happen if we reduce air pollution levels. It estimates that reducing particulate matter pollution across Europe by about 20 per cent by 2050 would prevent an estimated 482,000 premature deaths from a range of diseases.

What next?

It’s important to keep these risks in perspective; most lung cancer cases are still caused by smoking. But as we work towards a tobacco-free UK it’s important to look at what else we can do to halt the rising rates of cancer.

“As other health hazards like smoking come under control, urban air pollution becomes more of a problem,” says Professor David Phillips, a Cancer Research UK-funded expert in carcinogenesis from King’s College London.

He points out that not all sources of pollution are the same. “Diesel exhaust, being much higher in fine particulates than petrol exhaust, is now one of the major sources of air pollution in cities.”

As one of the report’s authors, Professor Jonathan Griggs, told the BBC this morning, we can all play our part in reducing pollution by using the car less often. Walking or cycling have the advantage of helping people keep active too.

But we also need governments and local authorities to work together to develop a comprehensive strategy to reduce air pollution. Options such as a network of low-emission zones should be considered as part of a wider package of measures to cut air pollution. And getting this right, say the report’s authors, will reduce the strain on the NHS, leading to even more benefits.

“As NHS costs continue to escalate due to poor public health – asthma alone costs the NHS an estimated £1bn a year – it is essential that policy makers consider the effects of long-term exposure on our children and the public purse,” said Griggs.

In their report, which you can read here, the authors recommend 14 sensible steps that policy-makers and authorities should take to combat the ill health caused by air pollution. These range from better monitoring and analysis, better education, and developing new technologies to track global air quality trends – and of course, more research.

It’s important that they’re taken seriously.