By Danielle Steenkamp
Posted on 18 April 2012
What is a cholesterol?
Cholesterol is a fatlike substance (lipid) present in cell membranes. It is a precursor of bile acids and steroid hormones. The body produces cholesterol in the liver and absorbs cholesterol from the diet. Cholesterol is only found in animal products (meats, dairy products, and eggs). It is not found in fruits, vegetables, nuts, grains, or other non-animal food. Cholesterol is essential to the body and is used to build cell membranes. It produces sex hormones, and forms bile acids necessary for fat digestion. Cholesterol travels in the blood in distinct particles containing both lipids and proteins (lipoproteins). Lipoproteins are an essential part of the complex transport system that exchanges lipids among the liver, intestine and peripheral tissues. Lipoproteins are classified by the thickness of the protein shell that surrounds the cholesterol. In order of decreasing density, the three major classes of lipoproteins are high-density lipoprotein (HDL), low-density lipoprotein (LDL), and very low-density lipoprotein (VLDL). Coronary heart disease is directly and linearly related to the levels of total cholesterol and LDL cholesterol, and inversely related to the level of HDL cholesterol.
Low-density lipoprotein (LDL), Very low-density lipoprotein and High density lipoprotein (HDL) cholesterol
Low-density lipoproteins serve as the primary transporter of cholesterol. Excess LDL-cholesterol stimulates the formation of plaque on the intima of the coronary arteries. Plaque formation reduces the cross-sectional area and obstructs blood flow in these arteries, eventually producing a myocardial infarction. VLDL is synthesized in the liver and is the primary transport mechanism for endogenous triglyceride. HDL-cholesterol is involved in the reverse transport of cholesterol to the liver. The HDL molecules are suspended in the plasma and protect the body by picking up excess cholesterol from the arterial walls and delivering it to the liver where it is metabolized. There are a variety of environmental, genetic, and pathologic factors that can alter cholesterol and triglyceride transport. Some factors are gender, age, body fat distribution, dietary composition, cigarette smoking, some medications, genetic inheritance, and routine participation in physical activity. When these factors combine to yield elevated blood lipid and lipoprotein concentrations, the condition is referred to as dyslipidemia and has several forms:
- Hyperlipidemia indicates elevated blood triglyceride and cholesterol
- Hypertriglyceridemia denotes only elevated triglyceride concentration
- Hypercholesterolemia implies only elevated blood cholesterol concentration
- Hyperlipoproteinemia denotes elevated lipoprotein concentrations
Triglycerides are a type of fat found in your blood. Your body uses them for energy. High triglyceride levels can raise your risk of heart disease and may be a sign of metabolic syndrome. Metabolic syndrome is the combination of high blood pressure, high blood sugar, high abdominal fat, low HDL cholesterol, and high triglycerides. High triglycerides are usually caused by conditions such as obesity, poorly controlled diabetes, an underactive thyroid, kidney disease, alcohol excess, and regularly eating more calories than you burn. The most common causative factors are obesity and physical inactivity
A healthy lifestyle may not only help prevent the development of atherosclerosis (a process in which the arterial wall becomes thickened), but may also lead to regression on coronary artery blockage. An appropriate diet and exercise program are two key elements recommended by professionals for a healthy lifestyle. Both factors may have favorable effects not only on serum lipid levels, but on other risk factors for CHD including obesity and hypertension. Regular physical activity can bring about beneficial changes in a person with normal lipid and lipoprotein concentrations as well as most persons with dyslipidemia. These changes include the following: Triglyceride concentrations are generally lower, HDL-C concentrations are typically higher (but not always), and enzyme activity in the metabolism of lipoproteins is increased. Regular physical activity, especially habitual aerobic exercise, positively affects lipid metabolism and lipid profiles. Regular endurance exercise usually lowers plasma triglycerides but rarely reduces total cholesterol (TC) and LDL-C levels in individuals with initially high levels unless dietary fat intake is reduced and body weight is lost. HDL-C increases in response to endurance training. This response appears to relate to exercise training dose (interaction of the intensity, frequency, and duration of each exercise session and the length of the training period). Research has shown that the weekly amount of exercise was more important for raising HDL than its intensity. Getting at least 120 minutes of exercise a week, in segments of at least 30 minutes apiece, appeared to be the best way to boost HDL. This sort of exercise will do more than just raise protective HDL. It will strengthen your heart and bones, improve your circulation, and be good for virtually every part of your body. Resistance training has no effect on blood triglyceride levels, and TC and LDL-C are lowered only when the training increases lean body mass and decreases relative body fat.
Cowan, R. E. & Nash, M. S., 2010. Cardiovascular disease, SCI and exercise: unique risks and focused countermeasures. Disability and Rehabilitation, 32(36):2228-2236.
Durstine, J. L. & Moore, G. E., 2003. ACSM’s Exercise management for persons with chronic disease and disabilities. 2nd ed. United States: Human kinetics.
Williams, M. H., 2005. Nutrition for health, fitness, & sport. 7th ed. New York: McGraw-Hill.
Williams, L. & Wilkens, L., 2006. ACSM’s Resource manual for guidelines for exercise testing and prescription. 5th ed. United States: American College of Sports Medicine.