Just what exactly is the risk of death from heart and lung disease due to air pollution in Beijing — or anywhere? It’s such an obviously important question that I’m always discouraged and annoyed that I can never find clear answers from any public health group or website. My expat patients always want to know, “with my __ years in Beijing, what’s the long term risk for me and my kids?” And for those who cannot choose to leave easily, i.e. the millions of local Beijingers who are born and raised here, what’s their lifetime risk? You think it’d be an easy question, yes?
No, it’s not. It’s incredibly complicated data to tease out from the research literature. There actually is a lot of data out there, but their conclusions are usually so arcane and user-unfriendly that I find them barely useful. So I’ve tried to make my favorite data more user-friendly, or at least create a starting point for discussion. And I think we do need a robust discussion, as I was actually surprised that the risk was lower than I had expected — at least when compared to other cities. Let’s jump in…
Lies, Damn Lies and Statistics
There are many ways to report mortality data, and perhaps the most user-friendly is life-expectancy data. One of the most famous papers analyzing US data, published in NEJM in 2009 by Dr C Arden Pope, stated that every decrease in PM2.5 of 10ug/m3 increased life expectancy by 0.61 years. Let’s just say this is generally accurate, and that the opposite is true, that an increase in similar PM would cause a decrease in life expectancy; then in Beijing, the average PM2.5 of 100 ug/m3 is about 9 times higher than a WHO recommended annual average of 10: thus 0.6 x 9 = 5.4 years of lost life from long-term living in Beijing. This “five years” number was also mentioned in Steve Andrew’s excellent analysis of the US Embassy data and has frequently been quoted.
But I’m still not happy with that “conclusion”, as this type of analysis is extremely risky:
- It assumes the dose response is linear and unending into infinity when a lot of data shows it is not, especially for heart disease. Studies implied there may be a leveling off of risk at PM2.5 concentrations over 50 ug/m3, and most of these studies were done at levels under 30, which is far below Beijing’s average.
- It assumes pollution subtypes are the same everywhere, which is likely untrue. Different molecules carry different risks, especially ones that directly cause cancers. So Beijing’s risks may be different than LA’s risks. In fact, a recent study from Xian showed only 0.2% increase in mortality per 10 ug/m3 increase of PM2.5, which is far lower than other large studies which were done mostly in Western cities much less polluted cities than Xian. These other studies usually showed 0.6-1% increase. If this data is considered accurate and is replicated in other Chinese studies, then is China’s air actually safer than we think (at equal levels of PM2.5)?
- And just from my gut instinct, that would imply that the average lifespan of all the world’s most super-polluted cities would be clearly at least 5 years shorter than in cleaner cities. And I just haven’t seen this data, nor have I heard of anyone publishing such alarming stats. You think that’d be front page news, no?
There’s another way of looking at mortality data which I think is important to grasp, and that’s via relative risks. It means that you’d have an x% increased risk of developing a disease when compared to normal risk and disease rate. I really like relative risks (RR for short) also because it’s easy to compare to other diseases and risks. I’ll demonstrate in a minute, but I found my favorite data in another of C Arden Pope’s research here, published just last November. He compared death rates from PM2.5 both from air pollution and also from smoking (secondhand and direct), and the results are important and fascinating.
Lung Cancer Rates Are Not The Same As Heart Disease Rates
The crucial point in Pope’s newer research is that the long-term mortality risks from inhaling PM2.5 are not the same for lung cancer and heart disease:
- Lung cancer risk increases linearly and dramatically with increasing PM2.5, climbing to a risk of 12.2 for a pack-a-day smoker and 19.8 for a 2-pack-a-day smoker. The equation: [RR = 1+0.3195(dose)0.7433]
- Heart disease risk increases not linearly but in a parabolic curve, and much less dramatically, with a steep initial curve that tails off and maxes out around 2.5 relative risk. This equation: [RR = 1+ 0.2685(dose)0.2730]
Here below is Pope’s important graph showing long-term mortality risks of PM2.5 on lung cancers (left) and cardiac disease deaths (right). The above formulas are on page 1619 of Pope’s paper.
At Last: Relative Risks For Air Pollution
Let’s use Pope’s formulas above to calculate what everyone wants to know: the long-term relative risks from different levels of air pollution. I got Beijing’s average AQI from a cool new website, foggybeijing.com, which analyzes the US embassy data from 2010 to present. The other calculations are described in my recent article comparing Beijing’s air to cigarettes:
- Beijing’s 2011 average PM2.5 AQI of 174 = daily 1.8 mg of inhaled PM2.5 = lung cancer deaths 1.49 RR (relative risk) and heart disease deaths 1.32 RR
- AQI200 = PM 150 = 2.7 mg = lung cancer death 1.67 RR, heart disease death 1.35 RR
- AQI300 = PM 250 = 4.5 mg = lung cancer death 1.98 RR, heart disease death 1.40 RR
- AQI500 = PM 500 = 9.0 mg = lung cancer death 2.64 RR, heart disease death 1.49 RR
In other words, living long-term in Beijing (at least 6 years in these studies) causes a 49% increase in lung cancer and 32% increase in heart disease deaths, when compared to perfectly clean air of 0 (although background baseline is 3-5 ug/m3). And even if the average was crazy-bad 500, which doesn’t happen anywhere in the world, the increased risk is around 50-150% higher.
So What Do Those Numbers Really Mean To You?
Is this data high or low for you? Personally for me, it’s lower than I had feared, but let’s break this data down even more, as I think keeping pollution risks in perspective is very important. For example, what’s the risk in Beijing when compared to other historically smoggy cities such as Los Angeles or London? Or in my previous paradise in San Francisco’s wine country? Let’s get the latest annual PM2.5 rankings from the Excel spreadsheet data from the World Health Organization (more info: http://t.cn/aexyqM):
- LA: 14.8 = 0.27 mg = lung cancer RR 1.12, heart disease death RR 1.19
- London: 13.5 = 0.24 mg = lung cancer RR 1.11, heart disease death RR 1.19
- Paris: 22.9 = 0.41 mg = lung cancer RR 1.17, heart disease death RR 1.21
- San Francisco: 9.2 = 0.17mg = lung cancer RR 1.09, heart disease death RR 1.17
So even in almost-perfect San Francisco (where fog truly is called fog and not smog), the death rate from the almost non-existent air pollution is still 9-17% higher than zero pollution. And in LA, the risks are 12-19% higher; in Paris the risk is around 20%. So for those of you who are constantly thinking of fleeing Beijing to “better” areas, you need to ask yourself: is your next city’s improved risk clinically and physically relevant? In other words, does it make sense to run away from Beijijng’s risks of 32-49% when your next city’s risks are also in double digits? Perhaps it does, perhaps not. As I said, it’s all relative; I just don’t picture most Parisians sitting in their cafes filled with angst about their 20% risk and wondering if it’s finally time to flee to Aix-en-Provence.
I think this brings up a big point that other people have pointed out: the individual risk of mortality from air pollution can be argued to be relatively small, but the overall population risk is enormous. In other words, each person’s increased risk is quite small (arguably), but when you multiply that one person by tens of millions, that still means there are hundreds of thousands of premature deaths annually in China caused by air pollution.
My Bottom Line
As I said before, I am a bit surprised that the risk isn’t as high as I had feared. Those numbers (1.32, 1.49) are hard numbers I’ve already internalized and accept. I personally think my overall health benefits in Beijing are far greater than the risks — from emotional state of mind to an amazingly cool job to expat perks, et al. Who can say if my increased optimism and energy from my great lifestyle isn’t extending my life more than air pollution is shortening it?
But I definitely am still convinced — more than ever — that the risk of air pollution is real, and I have no intention of throwing away my home air purifiers and N95 masks. I still worry about raising children here, as the data does show permanent lung damage in children. But I never want my readers to forget that we spend 90% of our time indoors, and we have control over our indoor environment with indoor air purifiers. I’ll bet that proper use of these can get your overall daily exposure down to Parisian ambiance.
So, I plan to ride this crazy-fun China wave for at least a few more years, and with continued common sense and preventive measures, I’ll be just fine. And if I ever get lung cancer some day and guiltily think about my past sins (was it the cigarillos?), I still wouldn’t regret it. I am burning brightly and living deeply, and I’m sharing an epic adventure with my wife, the most important person in my life — and I wouldn’t change a thing.
Coming Soon: More Perspective
Next week or two I will follow up with what I think are other important perspectives: comparing air pollution’s risks to other extremely common “lifestyle risks” such as no exercise; high salt diets; lack of fruits and veggies in your diet; obesity; high cholesterol; and smoking. As you will see, their relative risks for mortality are much higher than Beijing air’s 1.32 and 1.49. Especially with smoking, including victims of secondhand smoke; as Pope points out in the same study above, people exposed to secondhand smoke have a relative risk of death as high as 1.3 for lung cancer and 1.27 for heart disease. So where’s the national outrage in China over these victims? Where’s the perspective? Stay tuned…