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Cholesterol and Triglycerides - What You Need To Know

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Updated July 08, 2014

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

Everywhere you turn, you are admonished to pay attention to your cholesterol (and to a lesser extent, your triglyceride) levels. Cholesterol and triglycerides are two forms of lipid, or fat, that circulate in your bloodstream. They are both necessary for life itself. Cholesterol is necessary for building and maintaining key parts of your cells (such as your cell membranes), and for making several essential hormones. Triglycerides, which are chains of high-energy fatty acids, provide much of the energy needed for your tissues to function. So you can't live without them.

But when blood levels of cholesterol or triglycerides become too high, your risk of developing cardiovascular disease is significantly increased. And this is why you need to be concerned about your lipid levels.

This article, and the links it provides, will tell you what you need to know about cholesterol and triglycerides, and can help you learn whether you should be treated for elevated lipid levels, and what kind of treatment you should have.

Where Do Cholesterol and Triglycerides Come From?

There are two sources for cholesterol and triglycerides: dietary sources, and "endogenous" sources (that is, manufactured within the body).

Dietary cholesterol and triglycerides mainly come from eating meats and dairy products. These dietary lipids are absorbed through your gut,and then are delivered through the bloodstream to your liver, where they are processed.

One of the main jobs of the liver is to make sure all the tissues of your body receive the cholesterol and triglycerides they need to function. Generally, for about 8 hours after a meal, your liver takes up dietary cholesterol and triglycerides from the bloodstream. During times when dietary lipids are not available, your liver produces cholesterol and triglycerides itself. About 75% of the cholesterol in your body is manufactured by the liver.

Your liver then places the cholesterol and triglycerides, along with special proteins, into tiny sphere-shaped packages called lipoproteins, which are released into the circulation. Cholesterol and triglycerides are removed from the lipoproteins and incorporated into your body's cells, wherever they are needed.

What Are LDL and HDL?

LDL stands for "low density lipoprotein," and HDL for "high density lipoprotein." In the bloodstream, so-called "bad" cholesterol is carried in LDL, and so-called "good" cholesterol is carried in HDL. In most people, the majority of the cholesterol in the blood is packaged as LDL, and only a relatively small proportion is from HDL cholesterol.

Why Are High LDL Cholesterol Levels Bad?

Elevated levels of LDL cholesterol have been strongly associated with an increased risk of heart attack and stroke. It is thought by many experts that when LDL cholesterol levels are too high, the LDL lipoprotein tends to stick the lining of the blood vessels, which helps to stimulate atherosclerosis. So, an elevated LDL cholesterol level is a major risk factor for heart disease and stroke. This is why LDL cholesterol has been called "bad" cholesterol.

While there is no question that elevated LDL cholesterol levels contribute strongly to cardiac risk, in recent years experts have begun to question whether reducing LDL cholesterol levels itself necessarily reduces the risk. In particular, while lowering LDL cholesterol levels with statin drugs significantly reduces cardiac risk, reducing LDL cholesterol levels with other kinds of drugs has not been shown to do so. This is why the new guidelines on treating cholesterol relies so strongly on the use of statins.

Why Is HDL Cholesterol Called "Good" Cholesterol?

A lot of evidence has accumulated suggesting that higher HDL cholesterol levels are associated with a lower risk of heart disease, and conversely, that low HDL cholesterol levels are associated with an increased risk. For this reason, HDL cholesterol is commonly called "good" cholesterol.

Why is HDL cholesterol protective? It appears that the HDL lipoprotein "scours" the walls of blood vessels and removes excess cholesterol. So the cholesterol present in HDL is (to a large extent) excess cholesterol that has just been removed from cells and blood vessel walls, and is being transported back to the liver for processing. The higher the HDL cholesterol levels, presumably, the more cholesterol is being removed from where it might otherwise cause damage.

In recent years, the notion that HDL cholesterol is always "good" has come under fire, and indeed, it now appears that the truth is a bit more complicated than simply "HDL = good cholesterol." Pharma companies working hard to devise drugs for increasing HDL levels, for instance, so far have run into a brick wall - several drugs that successfully raise HDL levels have failed to improve cardiac outcomes. Results like these are forcing experts to come up with new thinking about HDL.

How Important Are Triglycerides?

While the association between triglycerides and the risk of heart disease has not been as clear as it is for cholesterol, in recent years several studies have established that people with elevated levels of triglycerides are indeed at increased risk.

What Causes High Cholesterol?

Elevated cholesterol levels can be caused by several factors, including heredity, poor diet, obesity, sedentary lifestyle, age, smoking, and gender (pre-menopausal women have lower cholesterol levels than men). Several medical conditions, including diabetes, hypothyroidism (low thyroid,) liver disease, and chronic renal (kidney) failure, can also increase cholesterol levels. Some drugs, especially steroids and progesterone, can do the same.

Testing For Cholesterol and Triglyceride Levels

Beginning at age 20, testing for cholesterol and triglycerides is recommended every five years. And if your lipid levels are found to be elevated, repeat testing should be done yearly.

Treating High Cholesterol Levels

Deciding on whether you ought to be treated for high cholesterol or high triglyceride levels, whether that treatment ought to include drug therapy, and which drugs ought to be used, is not always entirely straightforward. Still, if your cardiovascular risk is elevated, the right treatment aimed at your lipid levels can substantially reduce your chances of having a heart attack, or even of dying prematurely. So when it comes to treating cholesterol and triglycerides, it is important to get it right.

Sources:

Third report of the National Cholesterol Education Program (NCEP) Expert Panel on detection, evaluation, and treatment of high blood cholesterol in adults (Adult Treatment Panel III). Circulation 2002; 106:3143.

Grundy SM, Cleeman JI, Bairey Merz CN, et al. Implications of recent clinical trials for the National Cholesterol Education Program Adult Treatment Panel III guidelines. Circulation. 2004;110:227-239.

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