Atherosclerosis | Cholesterol and atherosclerosis | Understanding laboratory results | Bottom Line
Cholesterol is a vital lipid that plays a crucial role in our body, building cells and producing hormones and vitamins. Typically, our liver produces all the cholesterol we need. Cholesterol can become a problem due to the Western diet.
Cholesterol is commonly divided into LDL-cholesterol and HDL-cholesterol. However, contrary to popular belief, there are not two different types of cholesterol. There is only one type of cholesterol, which is transported by various types of lipoproteins. Transport vehicles, i.e., lipoproteins, are required because cholesterol cannot move independently in the bloodstream.
There are five types of "vehicles" that carry lipids like cholesterol and triglycerides inside arteries:
- HDL-lipoprotein (High density lipoprotein)
- LDL-lipoprotein (Low density lipoprotein)
- IDL-lipoprotein (Intermediate-density lipoprotein)
- VLDL-lipoprotein (Very low density lipoprotein)
- Chylomicrons
Cholesterol test measures the amount of cholesterol in lipoprotein packets circulating in the blood, which is why two names commonly refer to cholesterol:
- HDL cholesterol (HDL-C)
- LDL cholesterol (LDL-C)
Understanding the difference between cholesterol and lipoprotein is essential, even though their names can easily be confused. Cholesterol is a type of lipid. Lipoprotein is a transport vehicle that carries cholesterol. Of these, the quantity of lipoprotein- not cholesterol- is a significant risk factor for atherosclerosis. [2]
Atherosclerosis
Atherosclerosis, often called plaque, is the buildup of fats and cholesterol in the artery walls. This buildup can narrow the arteries, potentially blocking blood flow. Additionally, if the plaque bursts, it can result in a blood clot.
Atherosclerosis can lead to severe conditions, including coronary artery disease, carotid artery disease, peripheral artery disease, aortic aneurysms, and strokes. These diseases are the leading causes of death in many Western countries.
Cholesterol and atherosclerosis
The common belief that cholesterol causes plaque and plaque-related diseases is a common misconception, likely due to confusing terminology and oversimplification of the subject.
The issue is not the cholesterol but the amount of LDL- and VLDL-lipoproteins that carry cholesterol. If there are too many lipoproteins, they can get stuck and gradually build up in the artery walls over time.
Example:
- Let's picture arteries as highways. A car as a vehicle represents a lipoprotein, and the passenger is cholesterol.
- We aim to prevent accidents (cars crashing) because they cause traffic jams and blockages.
- Accidents are more likely with more cars on the road, regardless of how many passengers are in each vehicle.
- Therefore, the focus should be on decreasing the number of cars on the road, not so much passengers.
Understanding laboratory results
Historically, laboratory tests have focused on measuring the amount of cholesterol in plasma rather than the quantity of lipoproteins, which are the more accurate risk indicators. Therefore, it's vital to know how to interpret laboratory results correctly.
- The goal of a cholesterol test is to assess the risk of atherosclerosis.
- Therefore, we want to obtain as accurate a picture as possible of the amount of LDL- and VLDL-lipoproteins in the blood, as this best indicates the risk [3].
- Standard laboratory tests measure the amount of cholesterol, not the amount of LDL- and VLDL-lipoproteins.
- The amount of cholesterol is also an indicator of the amount of lipoproteins. A high LDL cholesterol level typically suggests a high amount of harmful LDL and VLDL lipoproteins. Usually, monitoring LDL cholesterol provides the necessary result.
- In about 25% of cases, cholesterol does not correlate with the amount of lipoproteins. A person may have low LDL cholesterol but still have high LDL lipoproteins, increasing the risk of atherosclerosis. Conversely, the amount of LDL cholesterol may be high, but the amount of LDL lipoprotein is low, indicating a lower risk.
- Contrary to old beliefs, HDL cholesterol or HDL lipoproteins do not reduce the risk of atherosclerosis if the LDL lipoprotein level is elevated. Practically, this means that monitoring LDL cholesterol suffices for risk assessment [1], [4].
- Total cholesterol sums the amount of LDL and HDL cholesterol. The result does not reveal anything about the amount of harmful lipoproteins, as it combines LDL cholesterol and HDL cholesterol.
- A reliable test is available for measuring LDL and VLDL lipoproteins. It measures the amount of apoB protein. This test is available from nearly all entities conducting cholesterol tests.
- ApoB protein can be considered a marker found in all harmful LDL and VLDL lipoproteins but not in HDL lipoprotein. By measuring apoB, we know the amount of harmful lipoproteins. The apoB test thus provides a more accurate picture of risk than cholesterol measurement [5].
- Triglycerides are lipids similar to cholesterol, primarily used by the body as an energy source. A high triglyceride level indicates an excess of lipoproteins in the blood.
Bottom Line
A cholesterol test measures cholesterol, not harmful lipoproteins. However, it serves as a good indicator of risk.
The most crucial result in the cholesterol test is the amount of LDL cholesterol. HDL cholesterol is insignificant, as high HDL cholesterol does not compensate for high LDL cholesterol.
If LDL cholesterol is within limits and lifestyle and blood pressure are in check, further testing is likely unnecessary.
If LDL cholesterol is elevated, conducting an apoB test can be sensible, as it provides accurate information on the amount of harmful LDL and VLDL lipoproteins.
If the amount of LDL cholesterol is high, it is advisable to consider lifestyle changes, discuss the topic and actions with your doctor, or determine the number of harmful lipoproteins with an apo B measurement.
References
[2] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7369156/
[3] https://pubmed.ncbi.nlm.nih.gov/27821191/
[4] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4103514/
[5] https://www.thelancet.com/journals/lanhl/article/PIIS2666-7568(21)00086-6/fulltext