‘Cholesterol’ is a word that means different things to different people which leads to confusion among clinicians and also in the general public. What does ‘high’ or ‘low’ cholesterol or even ‘good’ or ‘bad’ cholesterol actually mean? These phrases were attempts to make a complicated bit of medicine generally understandable but I think it has actually led to more confusion so here is a deeper explanation of what these tests actually are and why we use them.

Technically, cholesterol is a specific molecule which performs many essential functions such as keeping our cell membranes stable and providing an initial building block for hormones like estrogen and testosterone. It is part of a large group of molecules called “lipids” which includes all the fats and oils in the body. (This is why you might hear your cholesterol blood tests referred to as the “lipid profile” by some clinicians).

I’ll use the term ‘lipid’ from now on for cholesterol and fats because it is actually the more correct term.  

One of the features that draws all of the lipids together is that they do not mix with water. Anyone who has tried to make a mayonnaise or a salad dressing that contains oil and water will have seen this - unless you stir carefully the oil separates out and the mayonnaise splits. 

The tendency of lipids to form big globs when mixed in water poses a problem for transporting them in the blood, where blockages can be deadly. So the body packages them up with specialized proteins (called apolipoproteins) so they can be safely carried in the bloodstream. They are called “lipoproteins” because they are a combination of lipids and protein (medical terminology isn’t really that fancy when you get to know it!).

So, when we talk about “cholesterol levels” we really mean the levels of lipoproteins in your blood, and these can take several forms as we shall see. 

If you left a vial of blood standing upright for a day or so it would start separating into layers. The heavy cells and proteins would sink to the bottom and on the top you would see a creamy white layer containing all the lipoproteins.  

If you took this lipoprotein layer and spun it in a centrifuge you would find different types of lipoprotein particles settling into layers depending on how dense they are (more dense at the bottom, less dense at the top). This is where the idea of “high density lipoproteins” (HDL) and “low density lipoproteins” (LDL) comes from.   

Extensive research over the last fifty years has found that the total amount of lipoproteins in the blood, and the relative concentration of LDL and HDL, are significant predictors of death from heart disease or strokes. This is because LDL in particular seems to increase the formation of atherosclerosis in blood vessel walls. By contrast, HDL seems to be broadly protective against atherosclerosis - although this protection seems to go away when the levels are very high.

These relationships between the lipoproteins and heart disease risk are why measuring them regularly is so essential, and why medications like statins that lower the level of LDL are used to reduce the risk of heart attacks and strokes.

Separating the lipoproteins out by density is not very precise though. For example, the LDL level is often calculated by taking the amount of HDL away from the total amount of lipoproteins found in the blood (confusingly referred to as “total cholesterol” by most labs). This means that non-LDL particles with a different risk profile are often counted alongside the true LDL.

The other problem is that the levels of HDL and LDL vary slightly depending on when and what you last ate.

These tests are still useful but we can now do better by measuring the ‘protein’ part of the lipoproteins.

The most well known of these proteins in our panel is ‘ApoB’ (Apolipoprotein B) which is the main protein found in LDL. Interestingly it appears to be a more consistent marker of atherosclerosis risk and it also varies less between measurements - so it is more accurate. 

When we looked into the research we also found that the protein ApoA1, which is found in HDL, is protective against atherosclerosis and is a more useful predictor than the HDL level.

Testing both ApoB and ApoA1 also allows us to to look at the ratio between them which is another a powerful predictor of future heart attacks and strokes. We are excited to be adding both of these markers to our heart health panel in the near future.

In summary, there is a lot more nuance to heart disease risk than just thinking about ‘good’ and ‘bad’ cholesterol. Combining widely used markers like HDL, LDL, with the more precise ApoB and ApoA1, gives us a more reliable picture of your heart health and helps us plan effective strategies to keep you healthy for as long as possible.

PS. If you have reviewed our sample dashboard you might have noticed that we also test Lp(a) which is another apolipoprotein like ApoB. However the way we interpret this test is quite different and I have explained it separately here.  

Key Resources

• Information on cholesterol testing from the Canadian Cardiovascular Society: https://ccs.ca/cholesterol/
• More information on atherosclerosis from the charity Heart&Stroke:  https://www.heartandstroke.ca/heart-disease/conditions/atherosclerosis 

Main academic sources:

• Nordestgaard, Børge G., et al. "Fasting is not routinely required for determination of a lipid profile: clinical and laboratory implications including flagging at desirable concentration cut-points—a joint consensus statement from the European Atherosclerosis Society and European Federation of Clinical Chemistry and Laboratory Medicine." European heart journal 37.25 (2016): 1944-1958
• Canadian Cardiovascular Society. 2021 Dyslipidemia - Canadian Cardiovascular Society [Internet]. Canadian Cardiovascular Society. 2023. Available from: https://ccs.ca/app/uploads/2022/07/2022-Lipids-Gui-PG-EN.pdf

All the views expressed here are based on careful research conducted by the research team at Niahealth. However, in some places we have omitted certain details for the sake of clarity and simplicity. If you have any questions about our research or the content of this blog email our head of research Dr Robin Brown at : robin@niahealth.co