Cholesterol

Cholesterol is a form of lipid or fat. This is crucial in the formation and functioning of all cells within the human body. It is a waxy, fat-like substance found in every cell. Cholesterol is also important for the production of hormones, vitamin D, and bile acids, which aid in fat digestion.

1.0Structure and Properties of Cholesterol

Cholesterol Structure: 

There are mainly three components in the chemical structure of cholesterol. They are: 

1. Steroid Backbone: It is the core structure of cholesterol consisting of four fused hydrocarbon rings, say A, B, C, and D, as shown in the figure, which is the classic feature of all steroids. It is called backbone because it gives strength and rigidness to the structure.
2. Hydrocarbon Tail: A long hydrocarbon tail attached to the ring D, which is a non-polar (containing no charge) and hydrophobic (means to repel water) structure. 
3. Hydroxyl Group (-OH): It is a polar structure attached to ring A. It is a hydrophilic structure, hence allowing the cholesterol molecules to interact with water.  

Cholesterol Properties

1. Amphipathic Nature: It means that cholesterol possesses both qualities: hydrophilic (water-attracting) and hydrophobic (water-repelling). The hydroxyl group (-OH) attaches to the water molecule, making it hydrophilic, while the long hydrocarbon tail makes it hydrophobic.
2. Rigid and Flat: The four steroid rings give it a rigid and flat structure, which helps it insert between phospholipids in the cell membranes. This rigidity provides structural support to the cell membrane and cholesterol molecule itself.
3. Waxy and Solid at Room Temperature: At room temperature, cholesterol is a waxy substance because it contains hydrocarbon rings and a tail. It is usually solid at room temperature; because of that, it serves to allow for membrane stability by preventing membranes from becoming too fluid.

2.0Types of Cholesterol

• Low-density lipoprotein (LDL) cholesterol: It is sometimes called "bad cholesterol," as high levels of LDL-type cholesterol may contribute to plaque buildup in arteries, which increases the risk of heart stroke & stroke. Ideally, LDL cholesterol levels should be lower than 100 mg/dL for optimal health.
• High-Density Lipoprotein (HDL) Cholesterol: This is known as "good cholesterol" because it helps remove excess (unwanted) cholesterol from the bloodstream by transporting it to the liver for processing and elimination. A higher HDL cholesterol level is protective against cardiovascular diseases.
• Very Low-Density Lipoprotein (VLDL) Cholesterol: VLDL carries triglycerides, and when it is converted to LDL, it contributes to the build-up of plaque in the arteries. Hence, VLDL levels must remain at a low level.
• Non-HDL Cholesterol: This is obtained by subtracting HDL cholesterol from total cholesterol. It includes all of the potentially injurious lipoproteins, including LDL and VLDL. Elevated non-HDL cholesterol is a major risk factor for heart disease.

3.0Functions of Cholesterol

1. Cell Membrane Structure: Cholesterol helps maintain the structure of cell membranes. Without cholesterol, the cell membrane would not be able to respond to changes in temperature and handle mechanical stress. 

2. Hormone Production: Cholesterol is a precursor in the formation of many steroidal hormones such as Sex hormones (estrogen, testosterone, and progesterone), Corticosteroids (Cortisol), and Mineralocorticoids (aldosterone), etc. 
3. Vitamin D Synthesis: Cholesterol in the skin, when interacting with ultraviolet (UV) light from the sun, converts into Vitamin D, which is important for the skin as well as bone health. 
4. Bile Acid Production: Cholesterol is utilised by the liver to produce bile acids, which are vital for the proper digestive process and the absorption of fats & fat-soluble vitamins in the small intestine. 

4.0Cholesterol Levels and Testing

High Cholesterol levels, particularly LDL cholesterol, can lead to many health conditions, such as blockage of arteries due to plaque buildup, which decreases blood flow, increasing the risk of different heart diseases, heart stroke, and other cardiovascular problems.

Cholesterol Testing

Frequent monitoring of Cholesterol Levels is crucial for assessing the health conditions mentioned above. This can be done by a Lipid profile test, a blood test to measure total cholesterol, LDL, HDL, and other forms of lipids, and recommended every 4-6 years for people aged 20 or above. 

Cholesterol Levels by Age Chart

5.0Causes of High Cholesterol

• Diet: Diets high in saturated & trans fats, found in processed foods and fatty meats, can raise LDL cholesterol.
• Lack of Physical Activity: Inactivity contributes to higher LDL cholesterol and lower HDL cholesterol levels.
• Obesity: Extra weight raises LDL cholesterol and lowers HDL cholesterol.
• Familial hypercholesterolemia: it is a genetic disorder in which the body cannot remove LDL cholesterol effectively, which leads to high levels of LDL from an early age. 
• Other conditions: Conditions such as diabetes, hypothyroidism, and kidney disease may also increase cholesterol levels.

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