Cholesterol Formula

Cholesterol is a fatty steroid metabolite found in the cell membranes and transported in the blood of all animals. It is an essential structural component of cell membranes and an important precursor for the synthesis of bile acids, Vitamin D and steroid hormones such as the adrenal gland hormones cortisol and aldosterone as well as the sex hormones estrogens, progesterone, and testosterone. However, high levels of cholesterol in the blood circulation, depending on its form of transportation, are strongly associated with progression of atherosclerosis.

Most cholesterol, typically 80-90%, is synthesized within the body. In the U.S. population, typical total body cholesterol synthesis is about 1,000 mg/day, about 20-25% of which occurs in the liver. Typical dietary intake is usually 200-300 mg/day (essentially 0 mg/day for pure vegetarians). The body compensates for cholesterol intake by decreasing or increasing the amount synthesized. In the liver, cholesterol is converted to bile acids and excreted into the digestive tract to aid in the absorption of fat and the fat-soluble Vitamins A, D, E and K. About 50% of the excreted cholesterol is later reabsorbed by the small bowel back into the bloodstream for recycling.

VLDL, LDL and HDL
Because cholesterol is largely insoluble in water, it is transported in the water-based bloodstream within lipoproteins, which are complex spherical particles with a water-soluble exterior and a lipid-soluble interior. Triglycerides (a type of fat) and esterified cholesterol are carried internally while phospholipids and free cholesterol are contained in the surface monolayer of the lipoprotein particle.

There are several types of lipoproteins within blood called, in order of increasing density, chylomicrons, very-low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), low-density lipoprotein (LDL), and high-density lipoprotein (HDL).

VLDL molecules are produced by the liver and contain high levels of triglycerides. During transport in the bloodstream, the blood vessels absorb triglycerides and leave IDL molecules, which contain a higher percentage of cholesterol. Half of the IDL molecules are taken up by the liver and half continue to lose triglycerides in the bloodstream until they form LDL molecules.

LDL molecules are the major carriers of cholesterol in the blood. When this system is deregulated, high levels of LDL molecules appear in the blood and are taken up by macrophages, which become engorged and often get trapped in the walls of blood vessels and contribute to artherosclerotic plaque formation. These plaques are the main causes of heart attacks, strokes, and other serious medical problems, leading to the association of so-called LDL cholesterol (actually a lipoprotein) with "bad" cholesterol.

HDL particles are thought to remove cholesterol from cells and transport cholesterol back to the liver for excretion or to other tissues that use cholesterol to synthesize hormones in a process known as reverse cholesterol transport. Having large numbers of large HDL particles correlates with better health outcomes. Thus HDL is sometimes referred to as "good cholesterol".

High Blood Cholesterol (Hypercholesterolemia)
High blood cholesterol is a metabolic derangement that can be secondary to many diseases and can contribute to many diseases. Abnormally high cholesterol levels, especially higher concentrations of LDL and lower concentrations of functional HDL, are strongly associated with cardiovascular disease. This may be related to diet, genetic factors (such as LDL receptor mutations in familial hypercholesterolemia) and the presence of other diseases such as diabetes and an underactive thyroid.

• Diabetes
• Hypothyroidism
• Smoking and drinking
• High blood pressure
• Family history
• Poor diet
• Obesity
• Lack of exercise

Conditions with elevated concentrations of LDL particles are associated with atheroma formation in artery walls, a condition known as atherosclerosis, which is the principal cause of coronary heart disease and other forms of cardiovascular disease. In contrast, HDL particles have been identified as a mechanism by which cholesterol and inflammatory mediators can be removed from atheroma. Increased concentrations of HDL correlate with lower rates of atheroma progressions and even regression.

Elevated cholesterol does not lead to specific symptoms unless it has been longstanding. Longstanding elevated hypercholesterolemia leads to accelerated atherosclerosis, which can express itself in a number of cardiovascular diseases such as coronary artery disease (angina pectoris, heart attacks), stroke and short stroke-like episodes and peripheral vascular disease.

Blood Tests
When measuring cholesterol, it is important to measure its subfractions before drawing a conclusion as to the cause of the problem. For accurate measurements, eating or drink anything other than water should be avoided 9-12 hours before the blood sample is taken. The results may be interpreted according to the numbers below.

• <200 mg/dL: desirable
• 200-239 mg/dL: borderline high
• ≥240 mg/dL: high risk

• <70 mg/dL: optimal for people at high risk of heart disease
• <100 mg/dL: optimal
• 100-129 mg/dL: near optimal
• 130-159 mg/dL: borderline high
• 160-189 mg/dL: high
• ≥190 mg/dL: very high

• <40 mg/dL for men or <50 mg/dL for women: high risk
• 50-59 mg/dL: average
• >60mg/dL: desirable

• <150 mg/dL: normal
• 150-199 mg/dL: borderline high
• 200-499mg/dL: high
• >500 mg/dL: very high

Treatment
High cholesterol levels are often treated with medications, usually statins, combined with low-cholesterol diet. In strictly controlled environments, a specially designed diet can reduce cholesterol levels by 15%. In practice, dietary advice can provide a mild to modest decrease in cholesterol levels.

Dietary influence
Animal fats are complex mixtures of triglycerides, with lesser amounts of cholesterol and phospholipids. As a consequence, all foods containing animal fat contain cholesterol to varying extents. Major dietary sources of cholesterol include cheese, egg yolks, beef, pork, poultry, and shrimp. Cholesterol is not present in plant-based food sources.

Trans fats have been identified as a major dietary risk factor for cardiovascular diseases and should be avoided. Carbohydrates, especially more refined carbohydrates, have also been linked to increased levels of triglycerides and decreased levels of HDL in the blood.