Cholesterol is a waxy substance found in cells of the human body. Contrary to what most people think, cholesterol is not always bad. Cholesterol is a sterol and a fat-like substance that plays an essential role in regulating cell signalling to promote effective communication between the cells. Since cholesterol is important, 80% is produced by the body in the liver and intestine. The remaining 20% of cholesterol comes from food we eat.
Cholesterol cannot travel in the bloodstream on its own because it is fat. So, it merges with lipids to form a protein-covered particle called a lipoprotein. Lipoproteins can easily mix with the bloodstream and deliver fat and cholesterol wherever needed.
Cholesterol and lipids flow in different forms to make different types of lipoproteins. There are mainly five types of lipoproteins called Chylomicrons, Very-low-density lipoprotein (VLDL), Intermediate-density lipoprotein (IDL), Low-density lipoprotein (LDL) and High-density lipoprotein. Chylomicrons are formed in the digestive system through the food we eat and deliver fatty acids. VLDL are formed in the liver and deliver fatty acids to tissues. IDL are formed when cells extract fatty acids from VLDL, and the leftovers are either decomposed by the liver or converted into LDL.
The LDL has earned a reputation as bad cholesterol because it is pure cholesterol that collects in the tissue to form plaque. On the contrary, HDL is considered good cholesterol because it removes cholesterol from the circulation and sends it to the liver.
Cholesterol has been widely studied in the context of Alzheimer’s disease. In the brain, cholesterol is transported through apolipoprotein E (apoE). High cholesterol can induce the accumulation of toxic amyloid plaque – a hallmark condition of Alzheimer’s disease.
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