A lipoprotein is a particle that combines lipids (fats) with proteins, allowing fats to be transported in the water-based environment of the bloodstream. Fats are not water-soluble and cannot circulate freely in the blood, so the body packages them inside spherical particles where the water-repelling lipids are enclosed by a coat of proteins (called apolipoproteins) and phospholipids that are water-compatible. Different types of lipoprotein carry different proportions of fats, have different sizes, and serve different functions.
The main lipoprotein classes relevant to cardiovascular health are: very low-density lipoprotein (VLDL), which carries triglycerides from the liver to tissues; low-density lipoprotein (LDL), the primary carrier of cholesterol to tissues and the main driver of atherosclerosis; high-density lipoprotein (HDL), which transports cholesterol back to the liver for processing (reverse cholesterol transport); intermediate-density lipoprotein (IDL), a transitional particle; and lipoprotein(a) (Lp(a)), a modified LDL particle with an additional protein that increases thrombotic risk and is independently associated with heart attack and aortic valve disease.
LDL is often called ‘bad’ cholesterol because elevated levels promote the deposition of cholesterol in artery walls, leading to atherosclerotic plaques and coronary artery disease. HDL is called ‘good’ cholesterol because higher levels are associated with lower cardiovascular risk. Standard lipid blood tests report LDL cholesterol, HDL cholesterol, total cholesterol and triglycerides. For people at high cardiovascular risk, including survivors of cardiac arrest caused by coronary artery disease, NICE and ESC guidelines recommend an LDL target below 1.4 mmol/L.
Lipoprotein(a) is not included in routine lipid panels but is increasingly measured in people with premature cardiovascular disease or a strong family history. It is largely determined by genetics and does not respond well to standard lipid-lowering treatments. Specific therapies targeting Lp(a) are under clinical investigation.
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