The virus "Varicella zoster" that triggers chickenpox also causes shingles. Shingles affects the people with compromised immune function. Postherpetic neuralgia is the nerve pain that persists after other symptoms have cleared. The pain may or may not may persist in the area of the rash for many months after the rash disappears.
Coronary Heart Disease
The biggest cause of death in men and women in this country is coronary heart disease (CHD).
Many factors influence the risk of CHD. These include both non-modifiable factors such as inherited risks (reflected in family history), increasing age and male gender, and modifiable risks such as smoking, high blood pressure and high blood cholesterol levels. There is increasing evidence that many other factors, including lack of physical activity, being overweight, the distribution of body fat, lack of antioxidants, an abnormal response to insulin, abnormalities in blood clotting factors and high blood homocysteine levels also contribute to this condition.
Research has shown that a high blood cholesterol level is one of the major modifiable risk factors of CHD and that our lifestyles, and particularly the food we eat, can influence our blood cholesterol level and therefore our risk of heart disease.
The following key facts are designed to help dispel some of the myths surrounding cholesterol.
What 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 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.
Cholesterol is also present in some foods including eggs, butter and cream, liver and kidney. Average western diets are estimated to contain 250-750 mg per day, approximately half of which is absorbed by the intestine to enter the circulation.
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.
Body synthesis declines when more is absorbed from the diet, however some people are unable to regulate cholesterol homeostasis in this way.
What is the difference between blood cholesterol and dietary cholesterol?
Blood cholesterol is the level of cholesterol in the bloodstream.
Dietary cholesterol is the cholesterol present in some foods that we eat.
Is dietary cholesterol the main cause of high blood cholesterol?
Research has shown that the amount of fat in the diet - especially saturates - has a greater effect in raising blood cholesterol concentration than the amount of cholesterol in the diet*. Other factors, such as smoking, being overweight, and physical activity, also influence blood lipid and cholesterol levels. However, the overall risk profile for cardiovascular disease is far more complex and may be influenced by many other factors. Some of these, such as raised blood pressure, blood clotting factors and thrombotic tendency, and alcohol intake, are well established, whilst others e.g. blood homocysteine levels, and antioxidant status - influenced by the intake of antioxidant nutrients and phytochemicals - are the subject of ongoing research.
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.
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 (called "bad cholesterol") are associated with an increased risk of CHD. Much of the remaining cholesterol is carried as high-density lipoproteins (HDL), 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
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 the past decade. An early event is the dysfunction of the endothelial cells lining the arterial wall, resulting in a damaged area to which white blood cells (monocytes) are attracted. These cells are changed into macrophages and infiltrate the intima (the inner coat) of the arterial wall, taking up oxidised LDL cholesterol from the bloodstream. Repeated injury at the same site encourages the continuous build-up of lipid and other cellular products that constitute the atheroma, which may cause a fatal blockage of the arteries.
A high level of cholesterol-rich LDL is thought to be a factor that contributes to the initiation and maintenance of the process of coronary atherosclerosis. The antioxidant status of the arterial wall is another key factor in this process, and there is evidence that the presence of adequate antioxidants, such as vitamin E, may help protect against cholesterol-induced endothelial injury.
* Howell et al, American Journal of Clinical Nutrition, 65, 1747-1764, 1997 ** Hu et al, Journal of the American Medical Association, 281, 1387-1394, 1999
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