Cholesterol and triglycerides are important fats (lipids) in the blood. Cholesterol is an essential component of cell membranes, brain and nerve cells, and bile, which hekps the blood absorb fats and fat-soluble vitamins.
The body uses cholesterol to make vitamin D and various hormones, such as estrogen, testosterone, and cortisol. The body can produce all the cholesterol that it needs, but it also obtains cholesterol from food. Triglycerides, which are contained in fat cells, can be broken down, then used to provide energy for the body’s metabolic processes, including growth. Triglycerides are produced in the intestine and liver from smaller fats called fatty acids. Some types of fatty acids are made by the body, but others must be obtained from food.
Fats, such as cholesterol and triglycerides, cannot circulate freely in the blood, because blood is mostly water. To be able to circulate in blood, cholesterol and triglycerides are packaged with proteins and other substances form particles called lipoproteins.
There are different types of lipoproteins. Each type has a different purpose and is broken down and excreted in a slightly different way. Lipoproteins include chylomicrons, very low density lipoproteins (VLDL), low-density lipoproteins (LDL), and high-density lipoproteins (HDL). Cholesterol transported by LDL is called LDL cholesterol, and cholesterol transported by HDL is called HDL cholesterol.
The body can regulate lipoprotein levels (and therefore lipid levels) by increasing or decreasing the production rate of lipoproteins. The body can also regulate how quickly lipoproteins enter and are removed from the bloodstream.
Levels of cholesterol and triglycerides vary considerably from day to day. From one measurement to the next, cholesterol levels can vary by about 10%, and triglyceride levels can vary up to 25%.
Lipid levels may become abnormal because of changes that occur with aging, various disorders (including some hereditary ones), use of certain drugs, or lifestyle (suh as consuming a high-fat diet, being physically inactive, or being overweight).
Abnormal levels of lipids (especially cholesterol) can lead to long-term problems, such as atherosclerosis. Generally, a high total cholesterol level (which includes LDL, HDL, and VLDL cholesterol) or a high level of LDL (the “bad”) cholesterol increases the risk of atherosclerosis and thus the risk of heart attack and stroke. However, not all types of cholesterol increase this risk. A high level of HDL (the “good”) cholesterol may decrease risk, and conversely, a low level of HDL cholesterol increases risk. The effect of triglyceride levels on the risk of heart attack is less clear-cut. But very high levels of triglycerides (higher than 500 milligrams per deciliter of blood, or mg/dL) can increase the risk of pancreatitis. For people older than 20, levels of total cholesterol, triglycerides, LDL cholesterol, and HDL cholesterol after fasting should be measured at least once every 5 years. Collectively, these measurements are called the fasting lipoprotein profile.
Dyslipidemia
Dyslipidemia is abnormal levels of lipids (cholesterol, triglycerides or both) carried by lipoproteins in the blood. This term includes hyperlipoproteinemia (hyperlipidemia), which refers to abnormally high levels of total cholesterol, low density lipoprotein (LDL) – the bad-cholesterol, or triglycerides, as well as an abnormally low level of high density lipoprotein (HDL) – the good-cholesterol.
- Lifestyle, genetics, disorders, drugs, or a combination can contribute
- Atherosclerosis can result, causing angina, heart attack, strokes and peripheral arterial disease
- Doctors measure levels of high triglycerides and the various types of cholesterol in blood.
- Exercise, dietary changes, and drugs can be effective.
- Levels of lipoproteins and therefore lipids, particularly low density lipoprotein (LDL) cholesterol, increase slightly as people age. Levels are normally slightly higher in men than in women, but levels increase in women after menopause. The increase in levels of lipoproteins that occurs with age can result in dyslipidemia and increase the risk of atherosclerosis.
- A high level of high density lipoprotein (HDL) – the tood- cholesterol is beneficial and is not considered a disorder. A level that is too low is considered dyslipidemia and increases the risk of atherosclerosis.
- Factors that increase the risk of dyslipidemia include the following:
- Having close relatives who have had dyslipidemia (having a family history of the disorder).
- Consuming a diet high in saturated fats and cholesterol.
- Being physically active.
- Consuming, large amounts of alcohol.
Some people are more sensitive to the effects of diet than others, but most people are affected to some degree. One person can eat large amount of animal fat, and the total cholesterol level does not rise above desirable levels. Another person can follow a strict low-fat diet, and the total cholesterol does not fall below a high level. The difference seems to be mostly genetically determined. A person’s genetic makeup influences the rate at which the body makes, uses, and disposes of these fats. Also, body type does not always predict levels of cholesterol. Some overweight people have low cholesterol levels, and some thin people have high levels. Eating excess calories can result in high triglyceride levels, as can consumimg large amounts of alcohol.
Some disorders, including some hereditary disorders, cause lipid levels to increase. Diabetes that is poorly controlled or kidney failure can cause total cholesterol levels or triglyceride levels to increase. Some liver disorders and an underactive thyroid gland (hypothyroidism) can cause the total cholesterol level to increase.
Use of drugs such as estrogens (taken by mouth), oral contraceptives, corticosteroids, retinoids, thiazide diuretics (to some extent) and possibly antiviral drugs used to treat human immunodeficiency virus (HIV infection and AIDS can cause triglyceride level to increase.
Cigarette smoking, poorly controlled diabetes, or kidney disorders (such as nephritic syndrome) may contribute to a low HDL cholesterol level. Drugs such as beta-blockers and anabolic steroids can lower the HDL cholesterol level.
Treatment
Usually, the best treatment for people is to lose weight if they are overweight, stop smoking if they smoke, decrease the total amount of fat and cholesterol in their diet, increase physical activity and then, if necessary take a lipid-lowering drug.
A diet low in fats and cholesterol can lower the LDL cholesterol level. Experts recommend limiting calories from fat to no more than 25 to 35% of the total calories consumed over several days.
The type of fat consumed is also important. Fats may be saturated, polyunsaturated, or monounsaturated. Saturated fats increase cholesterol levels more than other forms of fat. Saturated fats should provide no more than 7 to 10% of total calories consumed each day. Polyunsaturated fats (which include omega 3 fats and omega 6) monounsaturated fats may help decrease levels of triglycerides and LDL cholesterol in the blood. The fat content of most foods is included on the label of the container.
Large amounts of saturated fats occur in many egg yolks, full-fat diary products, some nuts (such as macadamia nuts), and coconut. Vegetable oils contain smaller amounts of saturated fat, but only some vegetable oils are truly low in saturated fats.
Margarine, which is produced from polyunsaturated vegetable oils, was once thought to be a healthier substitute for butter, which is high in saturated fat (about 60%). However, some margarines (and some processed foods) contain trans fats, which may increase LDL (bad) cholesterol levels and lower HDL (good) cholesterol levels. Margarines made primarily from liquid oil (squeeze or tub margarines) contain less saturated fat than butter, contain no cholesterol, and contain fewer trans fats than stick margarines. Margarines that contain plant stanols or sterols can slightly lower total and LDL cholesterol levels.
Eating lots of fruits, vegetables and grains, which are naturally low in fat and contain no cholesterol, is recommended. Also recommended are foods rich in soluble fiber, which binds fats in the intestine and helps lower the cholesterol level. Such foods include oat bran, oatmeal, peas, rice bran, barley, citrus fruits, strawberries and apple pulp. Psyllium usually taken to relieve constipation, can also lower the cholesterol level.
Regular physical activity can help lower the LDL cholesterol level and increase the HDL cholesterol level. An example is walking briskly for 30 to 45 minutes 3 to 4 minutes a week.
Treatment with lipid-lowering drugs depends not only on the lipid levels but also on whether coronary artery disease, diabetes, or other major risk factors for coronary artery disease are present.
For people who have coronary artery disease or diabetes, the goal for the LDL cholesterol level is 100 mg/dL or less. Consequently, such people usually require lipid-lowering drugs. For example who do not have coronary artery disease or diabetes but have two or more other risk factors for coronary artery disease, the goal is 130 mg/dL or less. For those with one or no risk factors, the goal is 160 mg/dL or less.
There are different types of lipid-lowering drugs: bile acid binders, fibric and derivatives, niacin (a lipoprotein synthesis inhibitor), cholesterol absorption inhibitors, supplements of omega-3 fats, and statins. Each type lowers lipid levels by a different mechanism. Consequently, the different types of drugs have different side effects and may affect lipid levels differently. Following a low-fat when drugs are used is recommended.
Lipid-lowering drugs do more than lowering lipid levels – they also prevent coronary artery disease. In addition, niacin and statins have been shown to reduce the risk of early death.