Lipoproteins are fats that circulate in the bloodstream, according to Dr. Neil Campbell in the book "Biology." Some lipoproteins carry cholesterol, such as low-density-lipoprotein, or LDL, and high-density-lipoprotein, or HDL. Triglycerides are a type of fat and are also found in the bloodstream. Lipoproteins that carry triglycerides are often rich in cholesterol, contributing to atherosclerosis, or the hardening and narrowing of arteries, which may lead to high blood pressure, heart attack or stroke.
Cholesterol and Lipoproteins
According to the National Cholesterol Control Program, cholesterol is vital for proper health, but too much can contribute to heart disease. Cholesterol does not travel well in the bloodstream alone, so it combines with protein to be included in a lipoprotein. The lipoprotein transports cholesterol through the bloodstream.
LDL Cholesterol
When LDL carries cholesterol, the structure is called low-density-lipoprotein cholesterol, or LDL cholesterol. LDL cholesterol is often called the "bad" cholesterol. The majority of cholesterol in the bloodstream is carried by LDL cholesterol. LDL cholesterol becomes deposited along artery walls, which contributes to blocked blood vessels. Higher levels of LDL cholesterol indicate greater risk of heart disease. According to the American Heart Association, a LDL cholesterol concentration in the blood that is less than 100 milligrams per deciliter or, mg/dL, is considered "optimal." A person with a level between 160 to 189 mg/dL has a "high" concentration of LDL cholesterol, and an amount of 190 mg/dL and greater is considered to be "very high."
HDL Cholesterol
HDL cholesterol is also known as the "good" cholesterol, as HDL removes cholesterol from the blood and helps prevent cholesterol from building up in the artery walls. HDL transports cholesterol to the liver where cholesterol is turned into bile acid, which breaks down fats. Cholesterol is also carried to organs that produce essential hormones, including the ovaries, testes and adrenals. A "low" HDL cholesterol level is less than 40 mg/dL for women and less than 50 mg/dL for men, and increases the risk of heart disease, according to the American Heart Association. Having a HDL cholesterol level of 60 mg/dL or greater is "high" and protective against heart disease.
Total Cholesterol
Total cholesterol is a measure of LDL cholesterol, HDL cholesterol, and other lipids in the blood. Keeping total cholesterol levels below 200 mg/dL is recommended by the American Heart Association. A level above 200 mg/dL increases the risk of heart disease. Total cholesterol levels of 240 mg/dL and higher are considered high, and high levels double the risk of heart disease.
Triglycerides
Most fat in the body is stored as triglycerides. Only a small portion of triglycerides are carried in the bloodstream. However, high amounts of triglycerides in the blood increase the risk of heart disease. High blood triglyceride levels alone do not automatically contribute to heart conditions. According to the American Heart Association, other factors are usually involved to cause atherosclerosis among people with high triglyceride levels, such as having low HDL cholesterol levels or high LDL cholesterol.
References
- American Heart Association: Cholesterol
- "Biology"; Neil Campbell, Ph.D., Jane Reece, Ph.D., and Lawrence Mitchell, Ph.D.; 2001
- "Detection, Evaluation and Treatment of High Blood Cholesterol in Adults"; National Cholesterol Control Program of the National Institutes of Health; May 2001
