You learn something new every day: Cholesterol, a little like bacteria, comes in body "good" and "bad" forms. All those low-cholesterol spread adverts have been lying to us!
What's more worrying is that good cholesterol can change into bad cholesterol, and it could be car exhaust fumes that make it happen.
Researchers at UCLA have discovered that breathing in motor vehicle emissions alters the structure of high-density lipoprotein (HDL) cholesterol, changing it to low-density lipoprotein (LDL) cholesterol.
This latter cholesterol is the kind that clogs your arteries, producing symptoms ranging from slightly poorer health, to heart disease.
In addition, emissions can increase oxidation in cells, damage which can cause inflammation and hardening of arteries.
All this is bad news for the mice that were exposed to the vehicle emissions--for a few hours, several days a week over two weeks, at concentrations of diesel particulate matter equivalent to the range that miners are exposed to.
That suggests it's bad news for you too--particularly if you live in a traffic-heavy area.
Following the tests, the mice were subjected to a further week of filtered air, but the damage wasn't reversed--once subjected to pollution, it seems, your body is in it for the long haul.
"This is the first study showing that air pollutants promote the development of dysfunctional, pro-oxidative HDL cholesterol and the activation of an internal oxidation pathway, which may be one of the mechanisms in how air pollution can exacerbate clogged arteries that lead to heart disease and stroke," said senior author Dr. Jesus Araujo, an associate professor at the David Geffen School of Medicine at UCLA.
HDL actually protects arteries, but following exposure to vehicle emissions its effectiveness was reduced, with damage caused by the LDL. The researchers even found that rather than protecting against oxidation, the "good" HDL actually worked with the "bad" LDL to cause even more damage.
"We suggest that people try to limit their exposure to air pollutants, as they may induce damage that starts during the exposure and continues long after it ends," said report author Fen Yin, a researcher in the division of cardiology at the Geffen School of Medicine
In the meantime, well, probably best to start buying plenty of cholesterol-reducing spread...