Cholesterol

High levels of cholesterol in the blood are probably the best known risk factor for coronary heart disease. Now a high cholesterol level means that your LDL in blood is high because LDL carries about two thirds of the cholesterol in blood. There’s no clear cutoff point for a high plasma cholesterol concentration. In the UK, it’s set at 5 millimoles per litre for borderline high. But the average plasma cholesterol level in the country is 5.5 millimoles per litre. So most people are borderline high or worse. So it’s a rather strange situation. You can bring down your plasma cholesterol level, the LDL level, by using drugs called statins, which pretty well everyone has heard of.

Now these will bring down your cholesterol by about 30% to 50% depending on the type of statin. And that will bring down the risk of getting a heart attack by about 25% to 50%. How does that work? They bring down the plasma LDL level so less LDL gets into the arterial wall and so atherosclerosis doesn’t proceed so fast. Also if you’ve got a high cholesterol level, your platelets are more likely to aggregate and form a thrombus. So statins should bring down that risk as well. As well as bad cholesterol (LDL) there’s good cholesterol, HDL, or high-density lipoprotein. Now the higher your HDL, the less your risk of getting a heart attack.

It’s interesting that HDL is higher in women than in men. And women get coronary heart disease about ten years later than men do. At the menopause, however, the HDL is about the same in men and women.

So how does HDL work? Well, we’re not quite sure, but we think that it may work in the reverse way to LDL. LDL takes cholesterol from the blood into the arterial wall. HDL may take it the other way from the arterial wall from atherosclerotic lesions back into the blood. Another mechanism by which HDL may be protective is that it contains an enzyme called paraoxonase. This inactivates some inflammatory factors. And don’t forget atherosclerosis is an inflammatory disease. In fact, it was discovered here at the University of Reading that HDL contains paraoxonase. A better marker of the risk of coronary heart disease than LDL alone is the ratio of LDL to HDL.