What is Cholesterol?
Cholesterol; from Greek, chole AND steros, solid.
Meaning; white crystalline substance found in animal tissues and various foods, cholesterol is normally made by the liver and is an important constituent of cell membranes and a precursor to steroid hormones.
The human body is exposed two sources of cholesterol - those we produce and those we eat when consuming animal products. The amount we produce in our own body is far more significant than the cholesterol we consume.
Why is Cholesterol important?
Cholesterol is essential for the structure and function of all cells in the body. It is vital for the synthesis of hormones, vitamin D and other substances. It also helps with the protection, insulation ans signalling of nerve cells.
In the liver, cholesterol is converted to bile and bile salts. These bile salts are needed for the absorption of essential nutrients including vitamins A, D, E and K.
Lipoproteins and Cholesterol
As cholesterol is a fatty/waxy substance, it needs to bind to something in order for it to be transported in the body in the blood stream. Cholesterol and triglycerides (tg) are transported by lipoproteins. These lipoproteins will appear on your lipid profile test, and may be mentioned in by your GP when discussing your cholesterol levels.
The most commonly discussed types are LDL and HDL cholesterol. However there are more than two main types of lipoproteins.
The main types of lipoproteins:
- VLDL - very low density lipoproteins
- LDL - low density lipoproteins
- IDL - intermediate density lipoproteins
- HDL - high density lipoproteins
- Chylomicrons - a lipoprotein that is composed of cholesterol, triglyceride, and apolipoprotein B 48 and carries triglyceride to the liver.
Most cholesterol tests will measure only on your LDL and HDL levels and maybe your circulating triglycerides.
This is because low density lipoproteins (LDL) carry 75% total cholesterol in blood and carry it from the liver to cells of the body (LDL-C).
High density lipoproteins (HDL) remove excess cholesterol from body cells and blood and transport it to the liver and prevents the accumulation of cholesterol in blood which can reduce the risk of cardiovascular disease.
As LDL has a higher level of cholesterol and triglycerides, it has become know as the 'bad' cholesterol. Conversely as HDL helps to prevent the accumulation of cholesterol in the blood, it has been dubbed the 'Good' or 'Happy' Cholesterol.
Excess cholesterol is common after illness where the body is under stress (Feingold & Grunfeld, 2015).
LDL particle size
For VLDL and LDL cholesterol particle size and density have increasingly been studied as markers in cardiovascular disease including atherosclerosis and also in diabetes.
It has been found that small LDL particle size (LDL-P) is greater indicator of risk for atherosclerosis, hyperlipidemia and peripheral artery disease than total LDL cholesterol content in those without a genetic link, particularly in women and particularly in women with diabetes.
But is not a clear marker in those with a genetic link (parents with coronary artery disease). This is why particle size is not found on GP blood tests and total LDL remains more of a concern.
Cholesterol and Atherosclerosis
When plaque (fatty deposits) clogs your arteries, that’s called atherosclerosis. These deposits are made up of cholesterol, fatty substances, cellular waste products, calcium and fibrin (a clotting material in the blood).
As plaque builds up behind the artery wall, the wall of the blood vessel thickens. This narrows the channel within the artery, which reduces blood flow. That, in turn, lessens the amount of oxygen and other nutrients reaching the body. The plaque may break off and be carried in the blood stream and may cause a blockage.
The narrowing of the artery can cause a blood clot to adhere to the artery wall this can happen in any artery in the body including the brain. If the blocked artery supplies the heart or brain, a heart attack or stroke can occur. If an artery supplying oxygen to the extremities is blocked, tissue death or PAD can result.
How are plaques formed in the artery?
Many clinical studies have shown that plaques may form as a result of damage to the endothelium and the glycocalyx. These are protective lining of blood vessels. When they are damaged they become 'leaky' allowing adhesion of foam cells to the artery wall.
When there is excess LDL or LDL cholesterol becomes oxidated (due to ROS - that's a whole other blog) or glycated (due to excess sugar/ultraprocessed foods) it triggers an immune response where macrophages engulf the damaged LDL to remove it from the body.
As the cell lining has become 'leaky' these foam cells are able to penetrate the artery wall and form adhesion sites. This causes inflammation. Once the macrophage is below the lining it tries to absorb the damaged LDL and this forms a foam cell. A build up of the cells results in plaque formation.
Various HDL particles can ease inflammation in artery walls, stimulate production of nitric oxide, a molecule that helps artery walls relax, and help prevent blood clots from forming inside arteries.
The function of HDL is dependent upon genetic, environmental and lifestyle factors. Modification of the protein or lipid components of HDL in certain conditions may convert the HDL particles from anti-inflammatory to pro-inflammatory
HDL particles can also become damaged by transfats, refined sugars and exposure to high levels of ultra-processed foods. These ultra-processed foods causes change and dysfunction in this lipoprotein making it pro-inflammatory and preventing it from removing oxidised LDL.
Some types of HDL are great at plucking cholesterol from LDL and artery walls while other types are indifferent to cholesterol, and some even transfer cholesterol the wrong way — into LDL and cells. - Harvard Health
Cholesterol as a heart health marker
While tests do exist to measure genetic profiles and for full lipid profiles, these are costly and not available through most healthcare practitioners.
Without the ability to screen each person individually to assess their individual markers and genetic profile, current advice is to keep your total cholesterol levels or TC at or below 5mmol/L with LDL at 3mmol/L or less and HDL at 1mmol/L or more.
New research shows that having a low HDL cholesterol level is a greater risk factor to cardiovascular disease including heart attack, stroke and atherosclerosis.
Those who have read reports about the 'Cholesterol myth' will be quick to point out that high LDL levels and the presence of cholesterol is not correlated to higher risk of CVD. And this is true to a certain extent. Your genetics, your liver function and your diet & lifestyle greatly effect how your body uses LDL in the body and whether or not it becomes oxidated or glycated or if your HDL becomes dysfunctional.
There are many individual biomarkers that will tell us this, but for the majority of people tests for this is financially out of reach.
In the absence of this data, what we can do is take the actions we know can impact your CVD risk the most - diet and lifestyle change.
Diet and lifestyle interventions
Diet and lifestyle changes like avoiding ultra-processed foods, sugars and refined grains are completely within your control. Protecting the endothelium by limiting exposure to cigarette smoke, excess alcohol, stress and processed foods is also something you can do to reduce your risk.
Supporting liver function and consuming functional foods which encourage HDL product, regulates LDL production and regulates TG are two main aims of a heart healthy diet and lifestyle programme.
Other dietary and lifestyle factors that can positively impact your hear health include:
- Mediterranean diet. Following a fibre rich and nutrient dense Mediterranean style diet, containing 'good' fats such and lower amounts of sugar and processed foods has been shown to improve heart health.
- Exercising more. Vigorous exercise is best for boosting HDL cholesterol, but any extra exercise is better than none. Even 30-50 minutes of walking per day can significantly improve your CVD risk.
- Losing weight. If you are overweight, losing 5% to 10% of your current weight can raise HDL cholesterol, along with reducing blood pressure and blood sugar.
- Cutting back on refined carbohydrates. Switching from refined carbohydrates to a high fibre diet and adding more lean protein to your diet is a good dietary approach to increasing HDL.
- Stopping smoking. Quitting can improve HDL cholesterol and do so much more for your heart and health as well as protecting your endothelial cells.
- Moderate alcohol intake. Drinking alcohol in moderation (no more than one drink a day for women, one to two for men) raises HDL - think Pinot Noir rather than G&T. If you don't drink, there's no need to start — exercise, losing weight, and other lifestyle changes are plenty.