Your blood and circulatory system serve as the transportation highway for your body. Because fats do not dissolve in water, and blood is primarily water, transportation of fats in the circulation presents a problem. To overcome this challenge, blood fats travel in water-soluble, protein envelopes. These fat-protein complexes are called lipoproteins. Good and bad cholesterol are two types of lipoprotein. The concentrations of good and bad cholesterol in your bloodstream affect your risk of developing heart disease.
Low-Density Lipoprotein
Low-density lipoprotein is called the "bad" cholesterol. LDL carries most of the cholesterol in your blood. It is called "low-density" because it has a low concentration of protein compared to the amount of fat in each particle. Think of LDL as a cholesterol depositor. This lipoprotein transports cholesterol from your liver and deposits it in your organs and tissues --- including in the cells that line your arteries. Abnormally high levels of LDL can lead to ongoing deposition of cholesterol in your arteries. Blockages, or plaques, form and reduce blood flow, which may eventually lead to organ damage due to oxygen deprivation.
High-Density Lipoprotein
High-density lipoprotein is the "good" cholesterol. It is called "high-density" because it has a high concentration of protein and a low amount of fat. Think of HDL as a cholesterol scavenger. It picks up excess cholesterol from your body tissues and transports it to your liver, which gets rid of the fat by incorporating it into bile. This process is called reverse cholesterol transport. When you eat, bile is secreted into your intestines. Some of the cholesterol-rich bile passes from your body in your stool. Healthy levels of HDL protect against the formation of plaques in your arteries, which lowers your risk of developing heart disease.
Healthy and Unhealthy Cholesterol Levels
When evaluating your blood fats, your doctor usually checks your good, bad and total cholesterol levels. For optimal health, your LDL cholesterol level should be less than 100 mg/dL. A level of 100 to 129 mg/dL is "near optimal." LDL levels of 130 to 159 mg/dL are borderline high; 160 to 189 mg/dL is high; and greater than 190 mg/dL is very high. With HDL cholesterol, the higher your level, the more protection for your heart. An HDL of 60 mg/dL or greater is optimal for heart health; a level of 40 mg/dL or less increases your risk of heart disease.
Factors That Influence Cholesterol
Your diet and activity level influence the levels of good and bad cholesterol in your body. A diet high in cholesterol, saturated fats and trans fats can increase your LDL to dangerous levels. A sedentary lifestyle may also contribute to high LDL and low HDL levels. A diet low in bad fats and high in fiber promotes healthy cholesterol levels. Regular physical activity also helps boost your good cholesterol level and keeps your LDL level low.
References
- The Medical Biochemistry Page; Lipoproteins; Michael W. King, Ph.D.; February 2011
- "Advanced Nutrition and Human Metabolism"; Sareen S. Gropper, Ph.D., Jack L. Smith, Ph.D., James L. Groff, Ph.D.; 2009
- American Heart Association; What Your Cholesterol Levels Mean; February 2011
- National Cholesterol Education Program; Adult Treatment Panel III At-a-Glance; May 2001
- The Medical Biochemistry Page; Cholesterol and Bile Metabolism; Michael W. King, Ph.D.; February 2011
