Azara Blog: A link between small particulate pollution and blood clots

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Date published: 2008/05/13

The BBC says:

Breathing in air pollution from traffic fumes can raise the risk of potentially deadly blood clots, a US study says.

Exposure to small particulates - tiny chemicals caused by burning fossil fuels - is known to increase the chances of heart disease and stroke.

But the Harvard School of Public Health found it also affected development of deep vein thrombosis - blood clots in the legs - in a study of 2,000 people.

Researchers said the pollution made the blood more sticky and likely to clot.

The team looked at people living in Italy - nearly 900 of whom developed DVT.
...
Researchers obtained pollution readings from the areas they lived and found those exposed to higher levels of small particulates in the year before diagnosis were more likely to develop blood clots.

The Archives of Internal Medicine report said for every 10 microgrammes per square metre increase in small particulates, the risk of developing a DVT went up by 70%.

This is a classic confusion between correlation and causation. In particular, people who are poor are more likely to be unhealthy (generally) so might be more susceptible to DVT. And people who are poor might well be more likely to live in areas with higher levels of small particulate pollution. So there could be other underlying causes for the observed correlation. As with most of these kinds of health studies, they have all sorts of plausible reasons which give credence to why the causation might be true (and it could be true, even though they haven't proven it). Of course this plausibility is why they can get away with implying that the correlation is a causation.

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