Cholestrol & Triglycerides

What Is Cholesterol? What Are Triglycerides?

Cholesterol and triglycerides are two forms of lipid, or fat. Both cholesterol and triglycerides are necessary for life itself. Cholesterol is necessary, among other things, for building cell membranes and for making several essential hormones. Triglycerides, which are chains of high-energy fatty acids, provide much of the energy needed for cells to function.

Where Do Cholesterol and Triglycerides Come From?

There are two sources for these lipids: diet and "endogenous" sources (that is, those manufactured within the body).

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

One of the main jobs of the liver is to make sure all the tissues of the body receive the cholesterol and triglycerides they need to function. Whenever possible (that is, for about 8 hours after a meal), the liver takes up dietary cholesterol and triglycerides from bloodstream. During times when dietary lipids are not available, the liver produces cholesterol and triglycerides itself.

The liver then packages the cholesterol and triglycerides, along with special proteins, into tiny spheres called lipoproteins. The lipoproteins are released into the circulation, and are delivered to the cells of the body. The cells remove the needed cholesterol and triglycerides from the lipoproteins, as they are needed.

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. Most cholesterol in the blood is packaged as LDL. Only a relatively small proportion is from HDL cholesterol. Thus, the total cholesterol level in the blood usually reflects mainly the amount of LDL cholesterol that is present.

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 Some Cholesterol Called "Good" Cholesterol?

Much evidence now suggests that higher HDL cholesterol levels are associated with a lower risk of heart disease, and that low HDL cholesterol levels are associated with an increased risk of heart disease. Thus, HDL cholesterol appears to be "good."

Why is HDL cholesterol protective? It appears that the HDL lipoprotein "scours" the walls of blood vessels and cleans out excess cholesterol. The cholesterol present in HDL is (to a large extent) actually excess cholesterol that has just been removed from cells and blood vessel walls, and is being transported back to the liver for processing.

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. Also, elevated triglyceride levels are very often strongly associated with other important risk factors, including low levels of HDH cholesterol, obesity, insulin resistance, diabetes, and a tendency toward excessive blood clotting.

Most of these risk factors associated with high triglyceride levels are part of condition called metabolic syndrome, a condition caused by excess weight and lack of exercise in people who are prone to develop insulin resistance. So, treating high triglyceride levels is most often not done in isolation, but requires treating the constellation of risk factors associated with metabolic syndrome.

What Can Cause High Cholesterol?

Elevated cholesterol levels can be caused by several factors, including heredity, poor diet, obesity, sedentary lifestyle, age, and gender (premenopausal 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. Drugs, such as steroids and progesterone, can do the same. 
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