1. Functions of cholesterol

Cholesterol is present throughout the body and is essential for life. It is a structural component of cell membranes and participates in the synthesis of steroid hormones and some vitamins (vitamin D) and in the synthesis of bile acids that aid digestion and absorption of dietary fats.

The body produces its own needs for cholesterol by the liver and is present in foods of animal origin in the egg yolk, meat and dairy products. Excess saturated fat in the diet increases blood cholesterol.

2. Types of Lipoproteins

Cholesterol is carried by lipoproteins from the liver tissue, where it is needed and is eliminated through the bile salts in the stool. Thus, it eliminates about one gram of cholesterol a day.

However, about 98% of bile salts from the gall bladder removed the reabsorb the large intestine (colon), returning to the liver to be removed again as bile (enterohepatic circulation).

Lipoproteins consist of a surface layer, water soluble and insoluble inner core. The exterior is composed of phospholipids, proteins and cholesterol. And the inside contains triglycerides and cholesterol esters (cholesterol molecule attached to a fatty acid).

Lipoproteins, depending on their density, fall into four main groups: the lower the density, the greater the proportion of fat.

- Chylomicrons. Among the lipoproteins, chylomicrons are the largest and the lower density, are formed by the dietary fat and cholesterol from intestinal wall cells. Carry triglycerides as an energy source to tissues that need it, by the action of an enzyme called lipoprotein lipase (LPL). If present in large amounts, for example after a fatty meal, make the blood plasma has a milky appearance.

- Very low density lipoproteins. Triglycerides also distributed to various tissues such as adipose tissue and skeletal muscle, where it is stored as energy source. By filtering out proteins and triglycerides, VLDL becomes LDL. VLDL levels are elevated in familial hypertriglyceridemia, familial combined hyperlipidemia, diabetes mellitus, high alcohol consumption and hypothyroidism.

- Low-density lipoproteins. They are rich in cholesterol particles and carry about 70% of total plasma cholesterol. Cholesterol is taken up by the cells when the lipoproteins that transport receptors bind LDL on the surface of cells and are transformed into free cholesterol and amino acids.

Disorders that are caused by defect or lack of LDL receptors are normally characterized by high concentrations of plasma cholesterol. When cholesterol is not removed properly and accumulates in the circulation, deposits in the artery wall, leading to increased coronary risk. This is the case of familial hypercholesterolemia.

- High density lipoproteins are formed mainly in the liver and are composed of 50% protein in addition to phospholipids and cholesterol. The term is usually known as HDL “good” cholesterol because it transports excess cholesterol from tissues (including the arterial wall) back to the liver.

Low levels of HDL cholesterol are predictive of coronary risk. Levels below 40 mg / day in men and 45 mg / day in women (HDL levels are higher in women), increased cardiovascular risk. The main goal of treatment in most hyperlipidemic patients is to reduce the risk of premature heart attack or angina, and replicability in people with previous coronary disease.