Introduction
Cholesterol is a type of fat in our body. It helps build cells, digest food and make hormones. In this article, we will explore the different types of cholesterol—what they do, how they affect our bodies and wellbeing, and how to prevent them from harming our metabolic health. They’re easy to manage, but first, you need to understand the difference between good and bad cholesterol.
Low-density lipoprotein (LDL) cholesterol is considered the ‘bad’ cholesterol because it contributes to fatty build-ups in the arteries (atherosclerosis). This narrowing of the arteries increases the risk of heart attack and stroke. In comparison, high-density lipoprotein (HDL) cholesterol can be considered the ‘good’ cholesterol because a healthy level may protect against this risk. HDL carries LDL (bad) cholesterol away from the arteries and back to the liver. The liver acts to remove this cholesterol from the body by breaking it down to be passed from the body.
Studies indicate that elevated plasma cholesterol levels contribute to cardiovascular diseases (CVDs). These elevated levels can also cause non-alcoholic steatosis hepatitis (NASH), liver disorders (such as non-alcoholic fatty liver disease), and metabolic diseases which are associated with oxidative stress (an imbalance between cellular reactive oxygen species production and antioxidant systems).
Elevated LDL cholesterol levels, among genetic and environmental factors, can induce the development of cardiovascular diseases even in the absence of other risk factors. An example of this is Nonalcoholic fatty liver disease (NAFLD), a chronic inflammatory disease characterised by lipid accumulation within the liver. Although a small amount of fat in the liver is healthy, it becomes a problem when fat accumulation reaches 5–10% of the liver’s weight. Comparison of plasma and liver lipid levels demonstrated an increase of triglycerides, cholesterol and free fatty acids in patients with NASH compared to patients without NASH. Additionally, studies show that enhanced oxidative stress leads to insulin resistance by insulin receptor signalling, resulting in reduced glucose entry into the cells. Thus, any excess glucose in circulation will be stored as fat in our bodies.
What is cholesterol?
Cholesterol is a fat-like substance and a vital compound for cell structure and function. It is essential for the synthesis or action of:
- Lipoproteins, which transport hydrophobic lipid molecules through blood plasma, water and other extracellular fluids
- Vitamin D and calcium metabolism
- Stress hormones cortisol and cortisone
- Bile salts and acids, which are essential for the digestion of food (food and metabolism)
- Aldosterone, a steroid hormone, which is essential for mineral and fluid balance
- Membrane integrity, particularly in the brain
A diet rich in triglycerides stimulates cholesterol synthesis. Triglycerides are a type of lipid (fat) found in the blood. After eating, the body converts excess calories it doesn’t need into triglycerides. Primary synthesis of cholesterol occurs in the small intestine and the liver; however, almost every cell can synthesise it. Cholesterol cannot be catabolised within the body and is excreted in the stool, mainly as bile products. Cholesterol can also be obtained through diet. It is found in animal products, such as full-fat dairy, red meat, processed meats, fried foods, eggs, shellfish, baked goods and more.
What are the different types of cholesterol/lipoproteins?
Very low-density lipoprotein (VLDL) is made by the liver and works mainly to transport triglycerides to cells.
Chylomicrons are large triglyceride-rich lipoproteins produced in enterocytes (a cell of the intestinal lining) that transports lipids from the small intestines to adipose tissue and the liver.
Low-density lipoprotein (LDL) cholesterol is a lipid produced by the liver that circulates in the blood. It transports cholesterol from the liver to cells in the body that need it. LDL is commonly referred to as the ‘bad’ cholesterol due to its association with the development of CVDs.
High-density lipoprotein (HDL) cholesterol is produced in the liver and the intestines. It works by collecting excess cholesterol from cells and taking it back to the liver. This process is the reason it is commonly referred to as the ‘good’ cholesterol.
What are the functions of HDL and LDL cholesterol?
HDL works to transport excess cholesterol from peripheral sites to the liver, where it can be removed from the body. By doing so, the risk of developing CVDs, such as atherosclerosis, is positively reduced. In addition, HDL has demonstrated anti-inflammatory and antioxidant effects in the body. HDL’s functional properties are predominantly anti-atherogenic, meaning it works to prevent or inhibit atherogenesis. HDL decreases endothelial dysfunction (which stops the endothelial layer from performing its functions adequately) and oxidative stress. It also increases nitric oxide production and endothelial cell survival, which all result in prevention against atherogenesis.
LDL makes up the majority of your body’s cholesterol. High levels of LDL have been linked to an increased risk of heart disease and stroke. However, cholesterol isn’t all dangerous. It is vital for numerous bodily functions, such as protecting our nervous system and synthesising healthy cells and hormones. For example, your brain contains approximately 25% of the total amount of cholesterol in your body. This is primarily through myelin, which insulates your nerves in the brain and spinal cord. Another example is how the body also needs cholesterol to create progesterone, estrogen and vitamin D.
How do HDL and LDL cholesterol affect metabolic health?
HDL cholesterol is not only thought to benefit cardiovascular health but may also improve glucose metabolism in skeletal muscle. HDL’s main protein component, apolipoprotein AI (apoA-I), directly increases insulin-independent glucose uptake and glycogen synthesis in human skeletal muscle cells and adipocytes. HDL also amplifies glycolysis, the process of breaking down glucose into energy, and mitochondrial oxidative phosphorylation (the process in which ATP is formed) rates of glucose in skeletal muscle. Studies also suggest that HDL restores defective insulin-stimulated glucose uptake and may play a role in preventing and managing type 2 diabetes, a metabolic disorder.
Metabolic syndrome is a condition made up of multiple risk factors specific for CVDs, such as high triglycerides, insulin resistance, hypertension, visceral obesity and low HDL cholesterol. Low HDL cholesterol is a diagnostic criterion for metabolic syndrome, which increases the risk of developing atherosclerosis. Less than 40mg/dL for men and less than 50mg/dl for women is considered low. When high LDL levels lead to atherosclerosis, hypertension also occurs, leading to further development of metabolic syndrome and the risk of heart attack/stroke.
Cholesterol and the heart
Epidemiological data compiled from 164 countries by the World Health Organisation revealed that people with the lowest total cholesterol levels have the highest mortality levels from all causes. The same data shows that CVDs occur in people with normal, low and high total cholesterol, meaning that total cholesterol is a poor marker when assessing cardiovascular risk. An increase in cholesterol may reflect increased demand for cholesterol’s anti-inflammatory function or the need for cholesterol to make hormones or even repair certain cell membranes.
The size of LDL and HDL particles has proven to be a more specific indicator of cardiovascular risk than their quantity. Studies show that people with small, dense LDL particles have a greater risk of coronary heart disease (CHD). Moreover, large, fluffy LDL particles may be protective. Large HDL particles have also proven to be better, as they can remove cholesterol from the blood and artery walls, and have greater anti-inflammatory and anti-clotting effects, meaning they protect your body from heart disease.
How does cholesterol affect the heart?
Elevated levels of LDL cholesterol and apolipoprotein B (apoB) 100, the main structural protein of LDL, have been directly associated with risk of atherosclerotic cardiovascular events, according to population studies. This is because LDL deposits within the artery walls and is engulfed by macrophages (immune cells that ‘eat’ LDL particles). These macrophages then become foam cells, which further promote inflammation and increase the development of atherosclerotic plaques. Over time, these plaques harden and narrow the arteries, limiting the flow of oxygen-rich blood to all organs, cells and tissues in the body. This leads to fatalities, such as heart attacks and strokes.
Cholesterol is important for the metabolism of vitamin D, which is also essential for maintaining a healthy heart. Sufficient levels of cholesterol are needed in skin cells to make vitamin D from sunlight. Vitamin D deficiency may lead to an increased risk of heart attacks, congestive heart failure, strokes and other conditions associated with CVDs.
Relationship with triglycerides
Triglycerides and cholesterol are fatty substances called lipids. Triglycerides circulate in the blood and store unused calories to provide the body with energy. They are made by the body and also obtained from diet. Cholesterol is made by the liver and supports the healthy function of the nervous system, hormone production and the building of cell walls. High triglyceride levels in the blood are as dangerous for the development of heart disease and high cholesterol.
You can determine your triglyceride levels through a blood test. There are three levels: normal/ideal, borderline high and high. Normal is less than 150 milligrams per decilitre whereas borderline high is 150 to 199 milligrams per decilitre. High levels are considered 200 to 499 milligrams per decilitre (mg/dL).
The most common cause of high triglycerides occurs from metabolic disorders, such as diabetes and obesity. High triglycerides are a sign that your body is not properly processing food into energy. This commonly appears as insulin resistance (when the cells don’t respond to insulin effectively), which further increases your triglyceride levels.
Still, it can also be affected by alcohol intake, sedentary lifestyle, medications and other inflammatory diseases. A combination of both high triglycerides and high cholesterol greatly increases the risk of fatty deposits in the arteries and, therefore, the risk of heart attack and stroke.
What are the causes of high cholesterol?
High total cholesterol and LDL can result from other metabolic disorders such as hypothyroidism, insulin resistance and early-stage diabetes, NAFLD or familial hypercholesterolaemia. High cholesterol may also arise from a diet high in unhealthy saturated fatty foods (such as fatty meats, dairy products, fried foods), smoking, an insufficient amount of exercise and high alcohol intake. Chronic stress can also cause high blood cholesterol levels.
Common causes of high cholesterol include the following:
- Stress: Cortisol and adrenaline are produced by your body in stressful situations, and these lead to inflammation and higher blood sugar. Over time, your liver can produce more cholesterol to break down these effects.
- Unfiltered coffee: Without a filter, diterpenes (oily compounds in the coffee beans) can seep into your coffee.
- Medications: Birth control, antivirals and some other medications can increase your cholesterol levels.
- Pregnancy: Fetuses need cholesterol to grow, so your body increases production through different phases of pregnancy.
- Too much alcohol: Your liver focuses on breaking down alcohol instead of breaking down cholesterol.
- Thyroid issues: If you have an underactive thyroid, your body is not producing enough hormones to break down cholesterol.
- High-sugar diet: Your liver may produce more cholesterol when excessive sugar is consumed.
- Type 2 diabetes: When your blood sugar is high, it attaches to cholesterol in your bloodstream.
- Liver impairment: Your liver helps break down cholesterol; if it is not functioning properly, cholesterol levels may spike.
- Menopause: As your estrogen drops, your cholesterol can increase.
- Sitting too much: Your body produces an enzyme to turn LDL cholesterol into HDL cholesterol, and if you sit for too long, your body produces it less.
- Kidney problems: Research shows that high cholesterol levels impair kidney function. On the flip side, nephrotic syndrome, which is a type of kidney disorder, actually increases your cholesterol levels.
Ways to reduce ‘bad’ cholesterol
Exercising more has been proven to have beneficial results when it comes to managing cholesterol levels. Regular physical activity can lower LDL cholesterol and triglyceride levels and increase HDL levels. When participating in resistance training, studies demonstrate how increased volume of movement (more sets or repetitions) has a greater impact on improving lipid profile than increased intensity (i.e. high weight, low repetition).
Being mindful of dietary fat intake can also help reduce LDL cholesterol. Reducing saturated fats (such as those found in red meat and full-fat dairy) and trans fats will promote a healthier cholesterol level. Instead, try to increase your intake of healthy Omega-3 fatty acids, which can be found in oily fish, such as salmon, mackerel, herring, sardines and anchovies. Omega-3 fatty acids have strong anti-inflammatory effects and evidence suggests that they may significantly reduce triglyceride levels. Omega-3 fats also protect the heart and blood vessels, helping to prevent disease.
Other ways to reduce your cholesterol include:
- Research suggests that a year after quitting smoking, your risk of heart diseases and other cardiovascular problems drops dramatically.
- Reducing your weight and sugary food intake both contribute to lower cholesterol.
- Drinking alcohol in moderation.
Conclusion
Cholesterol is a type of fat in our body produced by the liver. Within the normal healthy range, it helps build cells, digest food (through the production of bile salts and acids) and plays a vital role in the production of hormones. Within a healthy range, cholesterol has also proven to have beneficial anti-inflammatory and antioxidant-like effects.
LDL cholesterol is primarily labelled as ‘bad’ cholesterol due to its ability to form fatty deposits in the artery walls, leading to the development of atherosclerosis. Atherosclerosis causes the arteries to harden, making it harder for oxygen-rich blood to reach all other areas of the body. This can lead to fatal events such as heart attack and stroke.
HDL cholesterol is labelled as the ‘good’ cholesterol because it collects excess cholesterol from the body and returns it to the liver, preventing fatty build-ups in the arteries. HDL cholesterol may also benefit metabolic health by improving glucose intake and glycogen synthesis in human skeletal muscle. Low HDL cholesterol is a diagnostic criterion for metabolic syndrome, which increases the risk of developing atherosclerosis.
High cholesterol may occur due to a large dietary intake of saturated and trans fats, sedentary lifestyle, smoking and high alcohol intake. It may also occur due to other metabolic imbalances, such as diabetes, inflammation and obesity, or familial hypercholesterolaemia. High cholesterol can be managed through medications such as statins. However, by reducing intake of saturated fatty foods and increasing daily movement, cholesterol can be lowered naturally.
Disclaimer: The contents of this article are for general information and educational purposes only. It neither provides any medical advice nor intends to substitute professional medical opinion on the treatment, diagnosis, prevention, or alleviation of any disease, disorder, or disability. Always consult with your doctor or qualified healthcare professional about your health condition and/or concerns and before undertaking a new health care regimen including making any dietary or lifestyle changes.
References
- https://www.heartuk.org.uk/cholesterol/what-is-cholesterol
- https://www.mayoclinic.org/diseases-conditions/high-blood-cholesterol/in-depth/triglycerides/art-20048186
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6132555/
- https://my.clevelandclinic.org/health/articles/11920-cholesterol-numbers-what-do-they-mean
- https://www.heart.org/en/health-topics/cholesterol/hdl-good-ldl-bad-cholesterol-and-triglycerides
