Cholesterol

Topic Highlights

● Cholesterol is a fat-like substance produced by the liver and taken through food.

● It is an important component of the cell membrane.

● Cholesterol is important for the production of various hormones.

● This visual presentation outlines cholesterol metabolism, types of cholesterol, and their role in the human body.

● It also includes information on the complications arising from an increase in cholesterol and discusses preventative measures.

Transcript

Cholesterol is a fatty substance that forms an important part of the cell membrane. Cholesterol stabilizes a cell against temperature changes. It is a major part of the membranes of the nervous system and other tissues. Cholesterol is used to produce hormones, bile acid, and vitamin D.

Cholesterol originates from two major sources: dietary intake and liver production. Dietary cholesterol comes mainly from animal products and dairy products. Organ meats, such as liver, are especially high in cholesterol, while foods of plant origin contain no cholesterol.

After a meal, cholesterol is absorbed into the blood and is then packaged inside a protein coat. This cholesterol-protein coat complex called chylomicron is then transported to the liver. Cholesterol swimming by the liver, as well as any excess dietary cholesterol in the liver, is transported in the serum. Cholesterol is insoluble in water and is packaged in special molecular complexes called lipoproteins, synthesized by the liver in order to be transported in plasma. The lipoprotein particle is composed of an outer shell of phospholipid, which renders the particle soluble in water, a core of fats called lipid, including cholesterol and a surface apoprotein molecule that allows tissues to recognize and take up the particle.

Lipoproteins are characterized by their density. Very low density lipoprotein (VLDL) is rich in triglycerides, carries cholesterol and contains very little protein. Triglycerides are a type of fat used to store energy. Only small amounts are found in the blood. VLDL released into the plasma is converted into low density lipoprotein (LDL).

LDL transports cholesterol from the liver to the rest of the body. LDL is rich in cholesterol and accounts for more than 60% of the total plasma cholesterol. Thus LDL is known as 'bad cholesterol.' High density lipoprotein (HDL) removes excess cholesterol from the plasma membrane and transports it back to the liver for further processing. Thus HDL is considered the 'good cholesterol.'

A constant state of high levels of cholesterol is called hypercholesterolemia. Many factors, such as genetic makeup, a high fat diet, lack of exercise and being overweight, can elevate cholesterol levels. Uncontrolled diabetes, kidney and thyroid diseases can also elevate cholesterol levels. Smoking oxidizes the cholesterol, thus increasing the levels of LDL. Rarely, an inherited condition called familial hypercholesterolemia can cause premature elevation of cholesterol levels.

High cholesterol is a 'silent' condition that does not have any visible symptoms until an associated condition develops. When LDL levels are high, it may be released into the body tissues, such as the inner walls of arteries. Together with other substances it can form deposits called plaques that can clog these arteries. This is called atherosclerosis.

As blood viscosity increases with high cholesterol levels, the blood pressure increases in order to move blood more forcefully through the narrower passageway. When the arteries that feed the heart are affected it can result in a heart attack. If this affects the artery supplying the brain it may cause a stroke. Deposits of cholesterol can some times cause a thin, white line circling the edge of the cornea. Plaque dislodged from elsewhere can sometimes get lodged in the blood vessels of the retina. This usually does not cause any permanent impairment but is indicative of high levels of cholesterol.

A blood test can measure cholesterol levels accurately. Usually, a blood sample is taken after fasting for at least 12 hours. Avoid strenuous exercise for a day before the test. The test measures the lipoprotein profile including LDL, HDL, triglycerides and total cholesterol. If the results are abnormal it is advisable to take another test in a few weeks.

A C-reactive protein test may be added to the screening of cholesterol and other lipid tests to detect people at risk for a heart attack. This coupled with elevated levels of white blood cells and fibrinogen, associated with blood clotting, indicate inflammation in the arteries.

Lifestyle modifications including weight control and exercise are essential for managing cholesterol. Include a diet rich in fiber with foods such as whole grains, legumes, fresh fruits, and vegetables. Choose unsaturated fats such as vegetable oils over saturated fats found in animal products and transfatty acids found in fast foods and commercial products. Give up smoking and limit alcohol intake. If cholesterol levels are too high and cannot be controlled by lifestyle modifications alone, cholesterol lowering agents will be beneficial.