Cholesterol Triglycerides

What are triglycerides and cholesterol? They are two important fats (lipids) that are produced by the liver and circulate in the blood as components of larger molecules called lipoproteins. People with high cholesterol or triglyceride levels of these lipoproteins have a condition called hyperlipidemia.

What is Cholesterol?

Cholesterol is a waxy fat found in the body and, despite what you may have been told, is a necessary nutrient for the body. Cholesterol is used in the formation of cell membranes and plays an important role in hormone, bile and vitamin D production.

Cholesterol comes from two sources: the foods that we eat, such as meat, dairy products and eggs, and our own liver, which produces about eighty percent of all the cholesterol in the body. That means that only about twenty percent of our total cholesterol is obtained from food.

Since cholesterol is not water-soluble, the liver packages the cholesterol into tiny spheres called lipoproteins so that the cholesterol can be transported through the blood. The lipoproteins can be divided into two different categories: low density and high density lipoproteins.

Low Density Lipoproteins LDLLow density lipoprotein (LDL): LDL, often dubbed the “bad” cholesterol, carries most of the cholesterol in the blood and seems to play a role in the deposition of fat in arteries. These deposits result in blockages called plaque. In addition to narrowing the arteries and increasing blood pressure, plaque contributes to the hardening of artery walls, a condition known as atherosclerosis.

High Density LipoproteinsHigh density lipoprotein (HDL): HDL is known as the “good” cholesterol. HDL carries cholesterol from the blood back to the liver for elimination. It is also responsible for removing the plaque buildup along the artery walls. Elevated levels of HDL are very desirable because it helps to clear blockages in the arteries, reduces LDL and decreases blood pressure.

What are Triglycerides?

Triglycerides are lipids normally found in increased levels in the blood following the digestion of fats in the intestine. Consumed calories that are not immediately used are stored in fat cells in the form of triglycerides and are later released from fatty tissues when the body needs energy between meals.

The major transporter of triglycerides is a forerunner of LDL, a simpler molecule known as VLDL (very low density lipoprotein). As the VLDL loses triglycerides, the VLDL particle is converted into intermediate and then low density lipoprotein.

Over time, elevated triglyceride levels may result in pancreatitis — a condition that can cause malabsorption of nutrients and lead to diabetes. As pancreatitis progresses, damage can spread to other organs, including the heart, lungs and kidneys.

High triglyceride levels also promote the deposition of cholesterol in the arteries and are associated with known risk factors for heart disease. The exact role that triglycerides play as an independent risk factor is not yet clear because people with high LDL and low HDL levels also have high triglyceride levels.

Although These Researchers Beg to Differ…

One study by Koren-Morag, Graff and Goldbourt, published in the American Heart Association journal Circulation, found that individuals with elevated triglyceride levels have a nearly thirty percent increased probability of suffering a stroke, even after taking into account other risk factors such as cholesterol levels. One of the most important aspects of the study is that it clarifies the independent link of triglyceride levels to stroke, meaning that a causal relationship is likely.

Coronary artery cross-section showing plaque build up and  blockage.What is Plaque?

Excess LDL cholesterol clings to arterial walls as it is transported through the system. Macrophages eat the LDL and become “foam cells.” The cells eventually rupture and begin to form a lipid layer called plaque. Connective fibers form in and around the fatty layer, causing it to harden. Over time, the fibrous layer thickens, narrowing the arterial pathway. When calcium deposits form a crust, the plaque becomes brittle and is more likely to rupture.

The Problem With Plaque

High blood cholesterol levels increase the likelihood that the fat will be deposited as plaque on the inner surface of arterial walls. As these deposits increase, the channel of the artery narrows, contributing to an increase in blood pressure. To compensate, the heart must work harder to pump the same volume of blood through the narrower arteries. When the coronary arteries themselves are affected by plaque, the harder working heart receives less oxygen, thus increasing the risk of heart attack.

Plaque also contributes to hardening of the arteries, or atherosclerosis. This loss of flexibility in arterial walls elevates blood pressure, putting the heart at additional risk.

When the plaque deposits become unstable, they burst, releasing their cholesterol into the bloodstream all at once. This can trigger clotting in small coronary arteries. When the artery is completely obstructed, blood flow stops and a heart attack occurs.

Resources

American Heart Association. (2004). Cholesterol.

American Heart Association. (2002). High blood triglycerides are independent risk factor for stroke.

Cable News Network. (2000). Study: Heart risks rise with high triglycerides even if cholesterol normal.

HeartPoint. (1997). High cholesterol: The facts.

Lang, J. E. (nd). Assessment of risk of heart attack and stroke.

McKesson Clinical Reference Systems: Adult Health Advisor 2001.1. (2001). Triglycerides.

National Heart, Lung, and Blood Institute. (nd). Lipoproteins.

National Heart, Lung, and Blood institute. (nd). Unstable plaque.

National Heart, Lung, and Blood Institute. (2002). What is cholesterol and what does it have to do with heart disease?

Tanne, D., Koren-Morag, N., Graff, E., Goldbourt, U. (2001, December 11). Blood lipids and first-ever ischemic stroke/transient ischemic attack in the Bezafibrate Infarction Prevention (BIP) Regsitry: High triglycerides constitute an independent risk factor. Circulation 104(24), 2892-2897.