The World Health Organization tallied up all the deaths due to outdoor air pollution based on different causes, and the major killer isn’t what most people think.
Asthma, lung cancer, and emphysema come to mind when we think about air pollution. But lung problems are only a small portion of the deaths caused by air pollution. Lung problems don’t even count for half.
How exactly do people die from air pollution?
This graph shows the three major categories of deaths from air pollution. What would you think goes into those boxes?
My first thought would be lung cancer. Survey says?
Just 14%! Not nearly as large as I imagined.
Well, OK, lung cancer is just one type of lung problem. How about emphysema, bronchitis, and other lung diseases?
Hmm, we’re still only at 28% of deaths due to air pollution. So what’s hiding in that big blue piece of the pie?
Heart attacks, strokes, and other diseases in our blood vessels. Really? It makes so much sense to look at our lungs because that’s where the air goes. But it turns out that we’re looking in the wrong direction. We should’ve been looking here:
Does air pollution really affect our heart and blood vessels? Here are three points of evidence.
1. More people have heart attacks on days with bad air pollution
A study in Boston found that on days with higher particulate air pollution (blue line), more people had heart attacks (red line).
Now, we’re not talking about a wild epidemic of heart attacks. The base odds of heart attacks on any given day are low, probably one in millions. So a 50% increase is important, but it moves the odds from 1 in a million to 1.5 in a million.
2. Wearing a mask in polluted Beijing reduces blood pressure
But hey, heart attacks are for unhealthy old people, right? I’m just 32 years old. Well, two studies randomly assigned healthy adults in Beijing to wear a mask outside or not. No one had a heart attack, of course, but people without a mask had higher blood pressure and lower heart ratevariability.
3. Breathing purified air improves blood inflammation and constriction of veins
OK, OK. But maybe you’re a healthy young person, just 20 years old. Maybe your lungs are even “used to” the pollution. My friends in China joke that Chinese people have the strongest lungs in the world.
Researchers in Shanghai randomly assigned healthy college students to use a real purifier or a fake purifier for 48 hours in their dorm rooms. Here’s what the PM2.5 levels were like in their dorm with a fake purifier (blue) and a real purifier (yellow).
They tracked all sorts of effects on biomarkers. When they looked at effects on blood inflammation, the effects were pretty big!
Same for blood coagulation:
And constriction of veins:
But when they looked at effects on lung function, the effects were tiny and not statistically significant:
That blew my mind. All this time we were looking in the wrong place!
If someone in Beijing or Delhi fell over and died of a heart attack, would most people think, “Ah, air pollution…”? Before I saw this research, I wouldn’t have.
Bottom line: Even if we aren’t coughing, even if we don’t have asthma, air pollution is still taking a toll on our heart and blood vessels.
Thomas is an Associate Professor of Behavior Science at the University of Chicago Booth School of Business and the founder of, a social enterprise to help people in China breathe clean air without shelling out thousands of dollars for expensive purifiers.