What is cholesterol and how does arteriosclerosis develop?
The human body needs cholesterol to work properly. For example, cholesterol is needed to make certain hormones and it is an important building block for cell walls. But too much cholesterol in the blood can sometimes mean an increased risk of cardiovascular disease.
Cholesterol is needed by every cell in the human body. Most of it is made in the liver. Only a small proportion comes from our diet. The bloodstream transports cholesterol from the liver to the other organs and tissues in the body. Spare cholesterol is carried back to the liver in the bloodstream.
Although cholesterol is often referred to as a “blood fat,” chemically speaking that is not quite correct. But, like fats, cholesterol does not dissolve in water (or blood), so our bodies need a special system to transport it. Cholesterol is packed into tiny parcels in the liver. The parcels are made up of cholesterol, proteins, fats (lipids) and other things in our blood. They can be transported through our bodies in the bloodstream. Because they are mainly made up of lipids and proteins, the parcels are called “lipoproteins.” There are two different kinds of lipoproteins, which differ in how densely they are packed:
- “LDL” cholesterol: “LDL” stands for “low-density lipoprotein.” This type of parcel transports cholesterol from the liver to the rest of the body. High levels of LDL cholesterol are associated with a higher risk of cardiovascular disease, which is why it is sometimes referred to as “bad” cholesterol.
- “HDL” cholesterol: “HDL” stands for “high-density lipoprotein.” This type of parcel transports cholesterol back to the liver from the body’s organs and tissues. Because high levels of HDL cholesterol are associated with a lower risk of cardiovascular disease, it is sometimes called “good” cholesterol.
High cholesterol levels increase the risk of arteriosclerosis
In recent years, researchers have changed their mind about how LDL cholesterol influences the risk of cardiovascular disease. It used to be thought that excess cholesterol simply builds up on the walls of blood vessels. But that has turned out not to be true. Depending on their age and lifestyle, most people have small inflammations in the walls of their blood vessels. These can develop in different ways. In people who have high LDL cholesterol, the phagocytes (scavenger cells) in blood “eat” more cholesterol particles. This means that cholesterol is more likely to stick to the walls of affected blood vessels.
Inflammations can also weaken the blood vessel wall, which might then tear. If blood suddenly comes into contact with the cholesterol-rich deposits as a result, a blood clot might form. That is because our bodies try to seal the wound in the blood vessel wall, just like when scabs form if you cut your skin.
If this happens, the consequences will depend on various things, including how big the blood clot is. A big clot can completely block the blood vessel, causing a heart attack or stroke. But the blood clots that form are often only small – they fix the damage in the blood vessel wall and do not have any noticeable consequences. Then the cut heals on its own. This can lead to scarring and calcification of the blood vessel wall, which can gradually make the blood vessel narrower without blocking it completely. The blood vessel wall becomes thicker and stiffer. The medical term for the hardening of blood vessel walls is arteriosclerosis.
Inflammations can develop in any artery in the body. They are particularly dangerous in the large arteries that carry blood to the brain and heart. Narrow coronary blood vessels can cause chest pain (pectoral angina) during physical strain. If a coronary blood vessel becomes blocked, blood will no longer flow to part of the heart muscle, which might result in a heart attack. If a blood vessel in the brain becomes blocked, it might lead to a stroke.
Cholesterol levels do not tell us anything about how effective treatments are
High LDL cholesterol levels and low HDL cholesterol levels are recognized risk factors for cardiovascular disease. They can help get an idea of someone’s individual risk. But that does not mean that everything that can improve cholesterol levels, or claims to do so, is automatically good for your health. For example, one medication called torcetrapib was shown to be very effective at increasing “good” cholesterol levels and reducing “bad” cholesterol levels. But when the manufacturer did a study involving 15,000 people to see whether torcetrapib also prevented cardiovascular disease, the opposite was found to be true: it actually increased the risk of cardiovascular disease. So it was never approved as a medicine.
This example makes it clearer why it is so important to take factors other than cholesterol levels into account when assessing the advantages and disadvantages of treatments. There is a lot of advice out there about what to do about high cholesterol, and many treatments are available. But only some of them have been reliably proven to prevent serious health problems, such as heart attacks, and increase life expectancy.
Barter PJ, Caulfield M, Eriksson M, Grundy SM, Kastelein JJ, Komajda M et al; ILLUMINATE Investigators. Effects of torcetrapib in patients at high risk for coronary events. N Engl J Med 2007; 357(21): 2109-2122.
Kasper DL et al. Harrison’s Principles of internal medicine. New York: McGraw-Hill Companies. 19th ed. 2015.
Parhofer KG. The Treatment of Disorders of Lipid Metabolism. Dtsch Arztebl Int 2016; 113(15): 261-268.
Pschyrembel W. Klinisches Wörterbuch. Berlin: De Gruyter. 2014.
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