Despite its bad press, cholesterol is essential for sustaining life. Cholesterol helps to form the membranes of cells which make up our organs and body tissues. It also helps to make hormones and bile acids. The body can produce its own cholesterol in the liver, but we also acquire it from our diet. Cholesterol can be split into good (HDL) and bad (LDL). Total cholesterol measures all cholesterol, both good and bad to see if either is circulating in high or low amounts.
Cholesterol has an essential role in cellular membrane physiology, the absorption of nutrients from the diet, the metabolism of calcium, sexual reproduction as well as the salt and water balance within the body.
Cell membrane physiology
Cholesterol helps to make up the membrane of cells. The cholesterol helps to maintain healthy cells and in turn a healthy body – if it is kept in balance. An imbalance has been identified in diseases such as cancer and Alzheimer’s Disease. The function of a cell membrane is to keep the inside of a cell separate from the outside. Cholesterol helps to keep the membrane rigid and modulates the thickness and fluidity of the membrane.
Bile Salts and Hormones
Bile salts are the major constituent of bile – a fluid produced by the liver and stored in the gallbladder to emulsify fats. Cholesterol is converted to cholyl CoA which is an activated intermediate required to produce bile salts. Cholesterol is also a precursor for steroid hormones including sex hormones.
HDL AND LDL
The body’s supply of cholesterol is made in the liver but can also be ingested from food sources such as meat, eggs and dairy products. Cholesterol is carried around the body by lipoproteins, namely high-density lipoprotein (HDL) and low-density lipoprotein (LDL). The lower the density of the lipoprotein, the more amount of fat present within it. Therefore, LDL contains a high amount of fat. LDL’s principal role is to transport the cholesterol made in the liver to the tissues in the body where it can be used up. However, high plasma cholesterol levels mean it accumulates within the blood vessels.
HDL, on the other hand, has protective effects on the heart and blood vessels. It works like a scavenger by transporting excess cholesterol from the arteries to the liver. HDL is, therefore, a good biomarker for predicting cardiovascular risk.
Total cholesterol takes a measurement of the total HDL, LDL and triglycerides present in the blood. Triglycerides are a form of fat which forms part of the diet. They are mostly found in meat, dairy and cooking oils. The liver can make triglycerides. Wherever they come from, triglycerides have 2 functions:
High levels of LDL can increase the risk of heart disease or diabetes. The build-up of cholesterol on artery walls can lead to the restriction of blood flow to vital organs such as your heart and brain. The higher your cholesterol level gets the greater risk you are at developing coronary heart disease and angina, symptoms include:
Higher cholesterol also puts you at a higher risk of developing type 2 diabetes. This is where the body does not produce enough insulin, or the cells are unable to react to the insulin it does produce and so causes high blood glucose levels. Some of the symptoms associated with diabetes include:
A healthy lifestyle is a good way to keep your cholesterol levels under control. Exercise is a good way to increase your HDL levels. Giving up smoking, increasing your unsaturated fat intake and lowering your alcohol consumption are all beneficial to improving your HDL and lowering your LDL levels.
The Mediterranean Diet has been shown to be effective in preventing type 2 diabetes and keeping cholesterol levels low. The diet is characterised by a high intake of fruit, vegetables, nuts, olive oil and grains as well as a moderate consumption of fish and wine. The Mediterranean Diet promotes a low intake of processed and red meat as well as whole-fat dairy products such as milk and cheese.
For good cholesterol levels, these simple points can help:
Exercise is key to reducing the risk of cardiovascular disease and has been shown to reduce cholesterol levels. You should exercise for at least 30 minutes per day, 5 times weekly to maintain a healthy lifestyle and reduce cholesterol levels.
Aerobic exercise is particularly beneficial for heart health. It increases your heart and breathing rate gently and leaves you feeling warmer but you shouldn’t be gasping for breath. Activities include:
Using gym equipment like the treadmill, exercise bike, hill climber, rowing.
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 Grouleff, J., Irudayam, S, J., Skeby, K, K and SchiØtt, B. (2015). The Influence of Cholesterol on Membrane Protein Structure, Function, and Dynamics Studied by Molecular Dynamics Simulations. Biochimica et Biophysica Acta (BBA) – Biomembranes: 1848(9), pp 1783-1795.
 Berg J, M., Tymoczko J., L, Stryer, L. (2002). Biochemistry. 5th edition. New York: W H Freeman. Section 26.4, Important Derivatives of Cholesterol Include Bile Salts and Steroid Hormones. Available from: https://www.ncbi.nlm.nih.gov/books/NBK22339/
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 Heart UK. (2018). Triglycerides. Available at: https://heartuk.org.uk/health-and-high-cholesterol/triglycerides
 National Health Service. (2016). Diabetes. Available at: https://www.nhs.uk/conditions/diabetes/
 Heart UK. (2018). For Good Cholesterol Levels. Available at: https://heartuk.org.uk/files/uploads/documents/huk_fs_d02_forgoodcholesterollevels.pdf
 Mann, S., Beedie, C and Jimenez, A. (2013). Differential Effects of Aerobic Exercise, Resistance Training and Combined Exercise Modalities on Cholesterol and the Lipid Profile: Review, Synthesis and Recommendations. Sports Med: 44, pp 211-221.
 Heart UK. (2018). Physical Activity. Available at: https://heartuk.org.uk/files/uploads/documents/huk_fs_mfsB_physicalactivity.pdf