關于膽固醇的一些知識

嘉泰

Background on CholesterolWhat is cholesterol?
Cholesterol is a waxy substance, one of the wide range of fats (lipids) present in the body. It is essential to life.
Cholesterol is an important component of all cell membranes, with about 25% of the body’s total cholesterol in the cell membranes of the nervous system, where it is a major component of the fatty sheaths that insulate nerves.
It also provides the basic skeleton for the synthesis of many hormones – the sex steroids, such as oestradiol and testosterone, the steroid hormones synthesised by the adrenal gland, for example cortisol, as well as the precursor of vitamin D (7-dehydrocholesterol).
Cholesterol is also an essential precursor of the bile acids and is therefore vital to fat digestion. An adult body contains about 150g of cholesterol.How much cholesterol comes from the diet?
Although nearly all body tissues can synthesise cholesterol, most is synthesised by the liver and intestine. It is therefore naturally present in the blood, irrespective of dietary cholesterol intake. The liver must produce a certain amount of cholesterol - without it the body would cease to function properly. It is estimated that an adult synthesises 0.5-1.0g of cholesterol per day, which is more than would usually be absorbed from the diet.
The total amount of cholesterol in our bodies at any one time will depend on the amounts synthesised and excreted and the amount of dietary cholesterol absorbed. Usually only about one third of the cholesterol in the body comes from the diet.
In most people, body synthesis will decline when more is absorbed from the diet, however some people are unable to regulate cholesterol homeostasis in this way.What are LDL and HDL cholesterol?
Fats are mainly carried around the body bound to specialised proteins, the lipoproteins. These lipoproteins are in a constant state of flux as they deposit and receive their component lipids, and their chemistry and involvement in metabolism is complex.
In simple terms, most cholesterol in the blood (70%) is carried by low-density lipoproteins (LDL), which take cholesterol from the liver to body tissues. High blood levels of LDL-cholesterol (sometimes called "bad cholesterol") are associated with an increased risk of CHD. Much of the remaining cholesterol is carried as high-density lipoproteins (HDL), so-called "good cholesterol", which is involved in the disposal of cholesterol, and which is associated with a decreased risk of CHD.High blood cholesterol levels and CHD risk
Many factors influence the risk of cardiovascular disease, coronary heart disease (CHD) and stroke.
These include non-modifiable factors such as inherited risks (reflected in family history), increasing age and male gender, and the well-established modifiable risks such as smoking, raised blood pressure, elevated cholesterol levels, lack of physical activity, obesity and Type 2 diabetes. It is also recognised that many other factors, including the distribution of body fat, insulin sensitivity, antioxidant status, abnormalities in blood clotting factors, elevated homocysteine levels, vitamin D status and many more, may also contribute to CHD.
Coronary heart disease causes death when the blood supply to the cardiac muscle is severely impaired by an occlusion of the coronary arteries. There are two main aspects to this process: atherosclerosis and thrombosis.
The complex sequence of cellular events that causes the development of atheroma, essentially a chronic inflammatory condition, has been extensively investigated over recent decades.
A high level of cholesterol-rich LDL is believed to be one of several factors that contribute to the initiation and maintenance of the process of coronary atherosclerosis. The antioxidant status of the arterial wall is thought to be another key factor in this whole process.

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