The link between air pollution and heart disease

Now one of the reasons why someone might suffer a heart attack, slightly surprisingly, is air pollution. And according to the World Health Organisation (WHO), "air pollution is now the world's largest single environmental health risk", and rates of heart attacks and strokes surge on days with low air quality. Why though was always a mystery, until scientists in Scotland began asking volunteers to breathe in gold nanoparticles, Chris Smith spoke to David Newby, British Heart Foundation Professor of Cardiology at the University of Edinburgh.

David - What we know about the particles of air pollution is they’re tiny. They behave like a gas so they get really deep down right into the alveoli of the lungs, which is the base sack right at the very bottom. And we believe that some of these particles, either within cells or on their own, jump across into the bloodstream.

Chris - When you say jump across; so I breathe in some particulates from the street out there they’ll get right into the bottom of my lung and then they’re actually getting into the blood so particles of traffic pollution are travelling around my body, you think?

David - So that’s been one of our challenges actually to design a study to see whether they can actually get into the bloodstream. So we did this study taking gold nanoparticles and got people to breathe in a fine aerosol of these particles, which were the same size as you get out of a diesel engine, for example. The reason we chose gold is it’s not harmful; it’s inert. But the second reason is the body shouldn’t have any gold inside it so if we can find evidence of gold inside the body then it must have come from these inhaled particles.

So what we did is we got various people, healthy volunteers to begin with, to breathe in a very fine aerosol vapour of gold. And what we found was that when we took blood samples for them for days and hours after they breathed it in, we could start to detect the gold. And it’s present in their blood and it’s present in their urine, so not only had it gone into the blood, it had been filtered out by the kidney, gone into your bladder and there it was in your urine.

So the next thing we did was say well, that’s a bit scary, what about patients who’ve had a stroke or something like that? Because when you’ve had a stroke, if you have disease in your neck - your carotid artery - there’s often a furring up and plaque which is what causes heart attacks and strokes and these people often have that removed surgically. So what we did is we got them to breathe in the day before their operation some of the gold particles. They went through surgery and they took out this plaque, and then we analysed that plaque to see if we could see any gold in it and, low and behold, we did.

So what that’s telling us, is okay gold’s not the same as what comes out of an engine, but they’re the same size and we could prove that these particles have gone from the lung into the bloodstream, and actually gone to the diseased areas of the body. And that’s quite a powerful message really.

Chris - It doesn’t tell you though that when they get to that site in the body that they’re the cause of the mischief though?

David - Absolutely not, no. And what it’s just showing is that it gets to there. Now we have done some experiments looking at how blood vessels behave when you’ve been exposed to diluted diesel exhaust. So we did some studies in Sweden, they had an exposure chamber where we diluted down diesel exhaust and got people to cycle in it.

Chris - Hang on a minute. So you put people in a shed and pipe in diesel exhaust and say just breathe this on an exercise bike?

David - Yeah, it’s… yes. Some people have challenged us with that. In fact, the BHF, some of the office staff raised it with me, and I pointed out to them that the dilute exposure that we’re giving was the same as the pollution monitoring station round the corner from the British Heart Foundation headquarters.

Chris - So the average person wandering around in London is breathing in equivalent air quality to what your victims, if I can call them that, in your study were breathing?

David - Yes, essentially. I mean, on a polluted day, if you’re walking down Oxford Street that’s what you would be exposed to, so it is within the realms of real world. Now in some parts of the world it’s lower what we put in the chamber than what people will be exposed to walking around a major mega city.

Chris - And what happens?

David - What we found was when we tested their blood vessels, the blood vessels don’t relax as much. They don’t release as much of a certain protein which helps dissolve blood clots. And when we looked at how much the body forms blood clots, you're much more likely to form blood clots when you’ve been exposed. And all of these things we know are associated with why you have a heart attack.

The final thing that we did, we got some patients who’d had treatment for heart disease to wear a heart monitor. And when they cycled in the presence of the diesel exhaust then we could see two to three times higher stress in the heart than when they did the exact same exercise when it was filtered air and not dilute diesel exhaust. So there’s clearly a huge connection between an acute exposure and the physiology of the body and how it behaves.

Chris - Does that argue then that there’s not really any safe level of exposure?

David - At the moment what we have is associations. But the associations that we’ve looked at there doesn’t seem to be a bottom level that people have identified as yet, which is slightly worrying because you could say well you know, this is just a problem for the third world countries and mega cities that are polluted. But actually, even within current air quality standards, there’s evidence of still some residual risk and that if we get the air quality better, the risk will go down further.

Chris - London’s on that list. It’s got one of the worst air qualities in the world and this is a first world country. It’s one of the most important cities in the world.

David - It is. And we do need to do something about it. We need better active transport. We need people to get out of their cars, get on their bikes, walking, using vehicles that are low emissions. We need to do this together as a society.