Lipids are the building blocks of the fats and fatty substances found in animals and plants. They are microscopic layered spheres of oil, which, in animals, are composed mainly of cholesterol, triglycerides, proteins (called lipoproteins), and phospholipids (molecules made up of phosphoric acid, fatty acids, and nitrogen). Lipids do not dissolve in water and are stored in the body to serve as sources of energy.
Cholesterol is present in all animal cells and in animal-based foods (not in plants). In spite of its bad press, cholesterol is an essential nutrient necessary for many functions, including:
- Repairing cell membranes
- Manufacturing vitamin D in the skin
- Producing hormones, such as estrogen and testosterone
- Possibly helping cell connections in the brain that are important for learning and memory
Regardless of these benefits, when cholesterol levels rise in the blood, they can have dangerous consequences, depending on the type of cholesterol. Although the body acquires some cholesterol through diet, about two-thirds is manufactured in the liver, its production stimulated by saturated fat. Saturated fats are found in animal products (meat, egg yolks, high-fat dairy products) and tropical plant oils (palm, coconut)..
Saturated fats are found predominantly in animal products, such as meat and dairy products, and are strongly associated with higher cholesterol levels. Tropical oils -- such as palm, palm kernel, coconut, and cocoa butter -- are also high in saturated fats.
Triglycerides are composed of fatty acid molecules. They are the basic chemicals contained in fats in both animals and plants.
Lipoproteins are protein spheres that transport cholesterol, triglyceride, or other lipid molecules through the bloodstream. Most of the vascular effects of cholesterol and triglyceride actually depend on lipoproteins.
Lipoproteins are categorized into five types according to size and density. They can be further defined by whether they carry cholesterol or triglycerides.
Cholesterol-Carrying Lipoproteins. These are the lipoproteins commonly referred to as cholesterol.
- Low density lipoproteins (LDL). (Often called "bad" cholesterol.)
- High-density lipoproteins (HDL), the smallest and most dense. (Often called "good" cholesterol.)
- Intermediate density lipoproteins (IDL). They tend to carry triglycerides.
- Very low density lipoproteins (VLDL). These tend to carry triglycerides.
- Chylomicrons (largest in size and lowest in density).
Effects of Lipoproteins and Triglycerides on Heart Disease
Low Density Lipoproteins (LDL), the "Bad"Cholesterol. The main villain in the cholesterol story is low-density lipoprotein (LDL). Heart disease is is less likely to occur among people with the lowest LDL levels. Lowering LDL is the primary goal of cholesterol drug and lifestyle therapy.
Low-density lipoprotein (LDL) transports about 75% of the blood's cholesterol to the body's cells. It is normally harmless. However, if it is exposed to a process called oxidation, LDL can penetrate and interact dangerously with the walls of the artery, producing a harmful inflammatory response. Oxidation is a natural process in the body that occurs from chemical combinations with unstable molecules. These molecules are known as oxygen-free radicals or oxidants.
In response to oxidized LDL, the body releases various immune factors aimed at protecting the damaged arterial walls. Unfortunately, in excessive quantities they cause inflammation and promote further injury to the areas they target.
High Density Lipoproteins (HDL), the "Good" Cholesterol. High density lipoprotein (HDL) appears to benefit the body in two ways:
- It removes cholesterol from the walls of the arteries and returns it to the liver for disposal from the body.
- It helps prevent oxidation of LDL. HDL actually appears to have its own antioxidant properties.
- It might fight inflammation.
HDL helps keep arteries open and reduces the risk for heart attack. High levels of HDL (above 60 mg/dL) may be nearly as protective for the heart as low levels of LDL. HDL levels below 40 mg/dL are associated with an increased risk of heart disease.
Triglycerides. Triglycerides interact with HDL cholesterol in such a way that HDL levels fall as triglyceride levels rise. High triglycerides may pose other dangers, regardless of cholesterol levels. For example, they may be associated with blood clots that form and block the arteries. High triglyceride levels are also associated with the inflammatory response -- the harmful effect of an overactive immune system that can cause considerable damage to cells and tissues, including the arteries.
Cholesterol and Triglycerides Goals
Total cholesterol count includes measurements of LDL, HDL, and triglycerides. The following chart summarizes all lipid goals for adults.
Cholesterol Goals for Adults
Total Cholesterol Goals
Less than 200 mg/dL is desirable.
Between 200 and 239 is borderline.
Over 240 is high.
70 mg/dL is considered an important goal for very high-risk patients (recent heart attack; current active or unstable cardiovascular or cerebrovascular disease; or two multiple risk factors as defined below.)
Below 100 mg/dL is optimal for everyone. It should be the goal for high-risk people, including those with existing heart disease, diabetes, or two or more risk factors for heart disease; 70 mg/dL is an even better goal for these individuals.
130 mg/dL or below for people with two or more risk factors; 100 mg/dL is an optimal goal.
160 mg/dL or below for people at less risk (one or zero risk factors); 130 mg/dL is an optimal goal.
Anything above 160mg/dL is high, with levels above 190 being very high. LDL levels over 190 often require medication even with no other cardiac risk factors present.
Levels above 40 mg/dL are desirable; levels above 60 mg/dL are optimal.
Below 150 mg/dL is normal.
150 - 199 is borderline high.
200 - 499 is high.
Over 500 is very high.
Risk factors for heart disease include a family history of early heart problems before age 55 for men (before age 65 for women), smoking, high blood pressure, diabetes, being older (over 45 for men and 55 for women), and having HDL levels below 35 mg/dL. People with two or more of these risk factors may have a 10-year risk of heart attack that exceeds 20%, and may therefore need to aim for LDL levels of 100 mg/dL or below.
Cholesterol Goals for Children. In 2007, the American Heart Association established general LDL goals for children. LDL goals are 190 mg/dL or less for children with no additional heart disease risk factors and 160 mg/dL or less for children with additional risk factors (such as family history of high cholesterol, heart disease, and diabetes).