Lipids & Apolipoproteins

Lipids and apolipoproteins are special types of fats, such as cholesterol, found in your blood. One of the risk factors associated with heart disease is an increase in blood cholesterol levels and other lipids such as triglycerides. Many factors can cause an increase in cholesterol. The most common of these factors are underlying genetic disturbances, poor nutrition and metabolic diseases such as diabetes.

Blood Lipids

Blood lipids are composed of four major elements: cholesterol, triglycerides, phospholipids and apolipoproteins. Many of the altered lipid conditions that cause heart disease are the result of defective apolipoprotein molecules. Most of the lipids in the blood come from the foods you eat. Lipids can also be transported from one site to another in the body. For example, lipids are transported from fat or adipose tissue to the skeletal muscles during times of exercise to fuel the muscles. Generally blood lipids are highest after a meal.

Cholesterol

Cholesterol is one of the most important lipids in the human body. Cholesterol is essential for the normal function of all cells. It is only when cholesterol levels exceed the amounts the cells need that the risk of heart disease occurs. Cholesterol in the blood is classified by density, size and cholesterol content into five major groups: chylomicrons, very-low-density lipoproteins, intermediate-density lipoproteins, low-density lipoproteins -- LDL -- and high-density lipoproteins -- HDL.

Cholesterol and Risk of Heart Disease

HDL cholesterol is synthesized in the liver and often referred to as "good cholesterol." Medical studies have shown an inverse relationship between circulating HDL cholesterol levels and heart disease. This means the more HDL cholesterol you have, the less risk of developing coronary artery disease, or CAD. For every 1 mg/dL increase in HDL, there is an associated 2 percent to 3 percent decrease in the risk of CAD, according to research by Dr. P.K. Shah and colleagues published in the 2001 issue of "Circulation."

Apolipoproteins

An alphabetical nomenclature -- A, B, C, D and E -- is generally used to designate the apolipoproteins. Apolipoproteins help to regulate enzymes involved in fat metabolism and transport of lipids to the correct body tissues, such as the liver, where they can be metabolized. One of the most important apolipoproteins is apolipoprotein A1, or APOA1. APOA1 is the main component of HDL, and researchers have demonstrated an inverse relationship between the levels of APOA1 and heart disease.

Health Implications

Weight gain, physical inactivity and a diet high in saturated fats can elevate your blood lipids. The American Heart Association recommends checking your blood lipid profile every year. You can lower LDL cholesterol and raise HDL cholesterol by reducing red meats and dairy products in your diet and by engaging in regular physical activity. Before starting a diet or exercise program, consult with your doctor.