Understanding Circulatory Disease

What is the connection between cholesterol and circulatory disease?

Diseases of the circulatory system do not have a single cause. Figure 33–12 lists several factors that increase the risk of heart and stroke. Although many risk factors can be controlled, this can be difficult. In some cases, medications may not be accessible or may not be effective. For example, blood cholesterol levels can be difficult to control. But researchers have learned a lot about blood cholesterol levels, their connection to atherosclerosis, and how the condition can be managed.

What Is Cholesterol? Cholesterol is a lipid that is part of animal cell membranes. It is also used in the synthesis of some hormones, bile, and vitamin D. Cholesterol is transported in the blood primarily by two types of lipoproteins—low-density lipoprotein (LDL) and high-density lipoprotein (HDL). LDL is the cholesterol carrier that is most likely to cause trouble in the circulatory system because it becomes part of plaque. HDL, often called good cholesterol, generally transports excess cholesterol from tissues and arteries to the liver for removal from the body.

Measures of a person's blood cholesterol actually are measures of lipoproteins. Normal total blood cholesterol levels range from 100 to 200 milligrams per deciliter (mg/dL). A person's LDL level should be less than 100 mg/dL. A man's HDL level should be greater than 40 mg/dL; a woman's HDL level should be greater than 50 mg/dL.