Scientists at Imperial College London say that slow blood flow in arteries may hinder the protective effect of statins.
The researchers say that slow blood flow tends to reduce statins' ability to trigger production of beneficial antioxidant molecules.
Moreover, the body's own protective mechanisms also tend to fail in the same areas, leaving them vulnerable to damage.
These cholesterol-lowering drugs work by stimulating the production of beneficial antioxidants in the cells of the arteries, by boosting levels of a key enzyme, called heme oxygenase (HO-1).
The researchers examined that the antioxidant potency of statins in different parts of the circulation by measuring the amount of HO-1 in the endothelial cells that line the arteries.
It was found the increase in HO-1 induced by the statin was significantly higher in cells exposed to fast and regular blood flow than in cells where blood flow was sluggish or disrupted.
This shows that statins fail to work well in areas where the body's natural defences are weak.
"Arteries don't clog up in a uniform way," the BBC quoted researcher Dr. Justin Mason as saying.
"Bends and branches of blood vessels, where blood flow is disrupted and can be sluggish, are much more prone to fatty plaques building-up and blocking the artery.
"What we have shown is that those regions of the arteries most likely to become diseased are the same regions that may not be benefiting maximally from statin treatment, a double whammy," he added.
The study has been published in the Journal of Biological Chemistry.