To circulate in your blood, which is mainly water, cholesterol and triglycerides — a form of fat — must be carried by proteins called apoproteins. A lipoprotein is a combination of a lipid — a fatty substance in the blood — and an apoprotein.

The main types of lipoproteins are:

     Low-density lipoprotein (LDL). LDL cholesterol is sometimes called "bad" cholesterol because it transports cholesterol to sites throughout your body, where it's either deposited or used to repair cell membranes. But like hard water causing lime to build up inside plumbing, LDL cholesterol promotes accumulation of cholesterol in the walls of your arteries.

     High-density lipoprotein (HDL). HDL cholesterol is sometimes referred to as "good" cholesterol because it helps clear excess cholesterol from your body.

   Very-low-density lipoprotein (VLDL). This type of lipoprotein is made up of mostly triglycerides and small amounts of protein and cholesterol.

Having a low level of LDL cholesterol and a high level of HDL cholesterol is desirable for lowering your risk of developing plaques and coronary artery disease.

You may have high LDL cholesterol as a result of genetic makeup or lifestyle choices, or both. Your genes can give you cells that don't remove LDL cholesterol from your blood efficiently or a liver that produces too much cholesterol as VLDL particles. Your genetic makeup can also result in too few HDL particles.