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.

• Read more about the basics of cholesterol and lipoproteins.

What Are LDL and HDL?

LDL stands for "low density lipoprotein," and HDL for "high density lipoprotein." In the bloodstream, "bad" cholesterol is carried in LDL, and "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 appears 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.

Why Is HDL Cholesterol Called "Good" Cholesterol?

A lot of evidence now suggests 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. Because the higher your HDL cholesterol the better, HDL cholesterol is 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.

• Read how you can increase your HDL levels.

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.

• Read about high triglyceride levels and what to do about it.

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.

• Read about testing for cholesterol and triglycerides.

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.

• Read how to decide whether treatment for cholesterol is necessary.

• Read about choosing the right treatment for high cholesterol.

• Read about increasing your HDL cholesterol.

• Read about treating high triglycerides.

_{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.}