6.6 – Understanding Blood Cholesterol
Learning Objectives
- Compare and contrast the function of the different types of lipoproteins as well as their relationship to heart disease.
- Describe the relationship between dietary lipids and blood lipid levels.
You may have heard of the abbreviations L.D.L. and H.D.L. with respect to heart health. These abbreviations refer to low-density lipoprotein (L.D.L.) and high-density lipoprotein (H.D.L.), respectively. Lipoproteins are lipid transport vehicles characterized by size, density, and composition. As the size of the lipoprotein increases, the density decreases. This means that H.D.L. is smaller than L.D.L. Why are they referred to as “good” and “bad” cholesterol? What should you know about these lipoproteins?
Major Lipoproteins
Recall that chylomicrons are transporters of fats throughout the watery environment within the body. After about ten hours of circulating throughout the body, chylomicrons gradually release their triglycerides until all that is left of their composition is cholesterol-rich remnants. These remnants are used as raw materials by the liver to formulate specific lipoproteins. Following is a list of the various lipoproteins and their functions:
- V.L.D.L.s. Very low-density lipoproteins are made in the liver from remnants of chylomicrons and transport triglycerides from the liver to various tissues in the body. As the V.L.D.L.s travel through the circulatory system, the lipoprotein lipase strips the V.L.D.L. of triglycerides. Eventually, some of the V.L.D.L. will become L.D.L.’s.
- L.D.L.s. Low-density lipoproteins are commonly known as “bad cholesterol”. This is not an accurate description of a lipid transporter that delivers needed lipids to the body. Small L.D.L.’s can enter the walls of the blood vessels, become oxidized and cause damage. If L.D.L. levels are low in the body, there is less risk of this type of damage occurring. It is important that we understand their function in the body so as to make healthy dietary and lifestyle choices. L.D.L.s carry cholesterol and other lipids from the liver to tissue throughout the body. L.D.L.s is comprised of very small amounts of triglycerides and house over 50 percent cholesterol and cholesterol esters. How does the body receive the lipids contained therein? As the L.D.L.s deliver cholesterol and other lipids to the cells, each cell’s surface has receptor systems specifically designed to bind with L.D.L.s. Circulating L.D.L. in the bloodstream bind to these L.D.L. receptors and is consumed. Once inside the cell, the L.D.L. is taken apart and its cholesterol is released. In liver cells these receptor systems aid in controlling blood cholesterol levels as they bind the L.D.L.s. A deficiency of these L.D.L. binding mechanisms will leave a high quantity of cholesterol traveling in the bloodstream, which can lead to heart disease or atherosclerosis.
- H.D.L.s. High-density lipoproteins are responsible for carrying cholesterol out of the bloodstream and into the liver, where it is either reused or removed from the body with bile. You can think of them as the trash collectors of the body. H.D.L.s have a very large protein composition coupled with low cholesterol content (20 to 30 percent) compared to the other lipoproteins. Because these high-density lipoproteins act like trash collectors, they are commonly referred to as the “good cholesterol.”
Contrasting L.D.L. and H.D.L.
Heart attack and atherosclerosis are conditions often caused by cholesterol that has accumulated, oxidized, and thickened in the walls of arteries. H.D.L.s and L.D.L.s are directly connected to these life-threatening ailments. By comparing and contrasting the roles each of these lipoproteins serves in the health of the heart and blood vessels, you will be able to construct and evaluate a plan of action for your personal health. Consider the following lipoprotein facts:
- L.D.L./H.D.L. composition. L.D.L. is approximately 25 percent protein and 75 percent cholesterol and other fats. L.D.L. is bigger (yet lighter) and richer in cholesterol than H.D.L. H.D.L. is 50 percent protein and 50 percent cholesterol and other fats. H.D.L. is smaller, denser, and richer in protein.
- L.D.L./H.D.L. function. L.D.L.s carry cholesterol into cells for normal usage, but L.D.L.s can also deposit cholesterol into the walls of blood vessels, which can lead to harmful disease. H.D.L.s scavenge excess cholesterol from the cells, tissues, and blood vessels and deliver these back to the liver, where these are either reused or excreted.
- L.D.L./H.D.L. warnings. High L.D.L. values warn of increased health risks for heart disease, while high H.D.L. values indicate a reduced risk for heart disease.
- Oxidized L.D.L. L.D.L.s become more dangerous when oxidized. Oxidation is defined as the loss of electrons between two substances via a chemical reaction. If L.D.L. oxidation occurs, the oxidized L.D.L. is left unstable. Oxidized L.D.L. can speed up the process of plaque formation in the arteries. It is believed to hasten the deposition of cholesterol into the arterial walls and to induce a chronic inflammatory effect throughout the body’s vast network of vessels. This activity promotes atherosclerosis and significantly increases the risk for heart attack or stroke.
Blood Cholesterol Recommendations
For healthy total blood cholesterol, the desired range you would want to maintain is under 200 mg/dL. More specifically, when looking at individual lipid profiles, a low amount of L.D.L. and a high amount of H.D.L. prevents the excess buildup of cholesterol in the arteries and wards off potential health hazards. An L.D.L. level of fewer than 100 milligrams per deciliter is ideal while an L.D.L. level above 160 milligrams per deciliter would be considered high. In contrast, a low value of H.D.L. is a telltale sign that a person is living with major risks for disease. Values of less than 40 milligrams per deciliter for men and 50 milligrams per deciliter for women mark a risk factor for developing heart disease. In short, elevated L.D.L. blood lipid profiles indicate an increased risk of heart attack, while elevated H.D.L. blood lipid profiles indicate a reduced risk.
The University of Maryland Medical Center reports that omega-3 fatty acids promote lower total cholesterol and lower triglycerides in people with high cholesterol.1 It is suggested that people consume omega-3 fatty acids such as alpha-linolenic acid in their diets regularly. Polyunsaturated fatty acids are especially beneficial to consume because they both lower L.D.L. and elevate H.D.L., thus contributing to healthy blood cholesterol levels. The study also reveals that saturated and trans fatty acids serve as catalysts for the increase of L.D.L. cholesterol. Additionally, trans fatty acids lower H.D.L. levels, which can impact negatively on total blood cholesterol.
1 University of Maryland Medical Center. “Omega-3 fatty acids.” Accessed June 21, 2019.
Tools For Change
Being conscious of the need to reduce blood cholesterol means limiting the consumption of saturated fats and trans fats and replacing them with unsaturated fats. Remember that saturated fats found in some meat, whole-fat dairy products, and tropical oils elevate your total cholesterol. Trans fats, such as the ones often found in margarine, processed cookies, pastries, crackers, fried foods, and snack foods also elevate your cholesterol levels. Read and select from the following suggestions as you plan ahead:
- Consider planning your meals based on one of the following eating plans: Mediterranean, Healthy Vegetarian, or Healthy U.S. Style Eating Pattern
- Soluble fiber reduces cholesterol absorption in the intestine which results in lowering lipid levels in the bloodstream. Try eating more oatmeal, oat bran, kidney beans, apples, pears, citrus fruits, barley, and prunes.
- Fatty fish are heart-healthy due to high levels of omega-3 fatty acids that reduce inflammation and lower cholesterol levels. Consume mackerel, lake trout, herring, sardines, tuna, salmon, and halibut. Grilling or baking is best to avoid unhealthy trans fats that could be added from frying.
- Walnuts, almonds, peanuts, hazelnuts, pecans, some pine nuts, and pistachios all contain high levels of unsaturated fatty acids that aid in lowering L.D.L. Make sure the nuts are unsalted and consider eating them raw for the most benefit. Avoid sugary or salty nuts. One ounce each day is a good amount.
- Olive oil contains a strong mix of antioxidants and monounsaturated fat and may lower L.D.L. while leaving H.D.L. intact. Two tablespoons per day in place of less healthy saturated fats may contribute to these heart-healthy effects. Extra virgin olive oil promises a greater effect, as the oil is minimally processed and contains more heart-healthy antioxidants.
Testing Your Lipid Profile
The danger of consuming foods rich in cholesterol and saturated and trans fats cannot be overemphasized. Regular testing can identify whether you need to take action to help prevent any life-threatening events.
Current guidelines recommend testing for anyone over age twenty. If there is a family history of high cholesterol, your healthcare provider may suggest a test sooner than this. Testing calls for a blood sample to be drawn after nine to twelve hours of fasting for an accurate reading. (By this time, most of the fats from the previous meal have circulated through the body and the concentration of lipoproteins in the blood will have stabilized.)
According to the National Institutes of Health (N.I.H.), the following total cholesterol values are used to target treatment: National Heart, Lung, and Blood Institute, National Institutes of Health. “High Blood Cholesterol: What You Need to Know.” N.I.H. Publication No. 05-3290. (Revised June 2005). Section 2.01.
- Desirable. Under 200 milligrams per deciliter
- Borderline high. 200–239 milligrams per deciliter
- High risk. 240 milligrams per deciliter and up
Video: 6.6.1: Understanding Cholesterol
Learn about what exactly is Cholesterol, and why you should be concerned about it.
Author: Healthguru
Published on Oct 8, 2007
Key Takeaways
- Some of the major lipoproteins are V.L.D.L., L.D.L., and H.D.L.
- V.L.D.L. delivers triglycerides and other lipids to the body’s tissues and some slowly becomes L.D.L., the main transporter of cholesterol.
- L.D.L., or “bad” cholesterol, has low protein composition and high cholesterol content. High levels of L.D.L. have been shown to increase the risks of heart disease.
- H.D.L. or “good’’ cholesterol has a larger proportion of protein and a small cholesterol composition. H.D.L. scavenges excess cholesterol and returns it to the liver for reuse or disposal. A high level of H.D.L. reduces the risk of heart disease.
- It is important to maintain a healthy lipid profile with values as recommended by the N.I.H. in order to minimize the risk of heart disease. Consuming omega-3 fatty acids can help maintain a healthy blood lipid profile.
Discussion Starters
- Summarize the roles of L.D.L. and H.D.L. Explain why L.D.L. is termed “bad” cholesterol and why H.D.L. is termed “good” cholesterol.
- Explain oxidation and how it affects L.D.L. and contributes to heart disease.
- Describe the procedure and blood test for testing your lipid profile.
- Recall the desired lipid values set out by the N.I.H. Identify the desired total cholesterol, L.D.L., H.D.L., V.L.D.L., and triglyceride values.
- How has learning this information affected your motivation to eat a more healthy diet?
