Introduction to High Blood Cholesterol

What Causes High Blood Cholesterol?

Cholesterol is produced by the liver and is carried throughout the circulation by attaching to proteins. The cholesterol-protein combination "packages" are known as lipoproteins. There are two major types of lipoproteins:

• Low-density lipoprotein (LDL) - Also known as "bad" cholesterol, LDL is the major lipoprotein that transports cholesterol in the bloodstream. Too much LDL in the bloodstream is a risk factor for cardiovascular disease (heart attack and stroke).

• High-density lipoprotein (HDL) - Also known as "good" cholesterol, HDL is the body's major mechanism for removing excess cholesterol from the bloodstream. HDL carries the excess cholesterol in the bloodstream back to the liver where it is broken down and then eliminated from the body.

In general, the causes of high blood cholesterol or hypercholesterolemia, can be grouped into two major categories:

• Lifestyle factors
• Genetic factors

Lifestyle Factors

Lifestyle factors that can contribute to high blood cholesterol include:

• Obesity
• Lack of physical activity and exercise
• Consuming an unhealthy diet that contains excessive cholesterol

Genetic Factors

People with an inherited condition known as familial hypercholesterolemia (FH), which results from a defective gene that produces the LDL-receptor protein, are genetically predisposed to very high levels of LDL ("bad") cholesterol. The LDL-receptor protein plays a major role in regulating LDL cholesterol concentrations in the body. A defect in the gene that controls the production of the LDL-receptor protein can lead to defective clearance of LDL cholesterol from the body resulting in the accumulation of high LDL levels in the bloodstream.

There are two major types of familial hypercholesterolemia:

• Heterozygous familial hypercholesterolemia

  • only one defective gene that codes for the production of the LDL-receptor protein is inherited from one of the parents
  • this condition occurs in about 1 of 500 people
  • in people with this condition, LDL cholesterol levels are about two times higher than normal

• Homozygous familial hypercholesterolemia

  • two defective genes that code for the production of the LDL-receptor protein are inherited (one from each parent)
  • this condition is very rare and occurs in about 1 in a million people
  • this condition results in extremely high blood cholesterol levels with rapidly progressive atherosclerosis ("hardening" of the arteries)

Other Possible Causes of High Blood Cholesterol

Researchers have identified other factors that may contribute to high blood cholesterol in some people. These factors include:

• Increased sensitivity to dietary fatty acids - some people may be uniquely sensitive to saturated fatty acids resulting in abnormally high LDL cholesterol levels in the bloodstream.

• Menopause - the natural decline of estrogen levels that occurs in menopause may be a contributing factor to the increased LDL cholesterol levels that are usually observed in postmenopausal women.

• Hypothyroidism - people with hyperthyroidism (underactive thyroid gland) usually have higher LDL cholesterol levels in the bloodstream possibly due to the decreased production of the thyroid hormone thyroxine.

• Mental stress - people who experience periods of mental stress usually also tend to have higher levels of LDL cholesterol in the bloodstream due to increased secretion of adrenal gland hormones (corticosteroids and catecholamines) in response to the mental stress.

• Increased production of LDL by the liver - some people may develop high blood cholesterol levels if the liver produces too much LDL cholesterol and overwhelms the body's capacity to remove the excess LDL.