High cholesterol, or hypercholesterolemia, is a condition in which there are unhealthily high levels of cholesterol in the blood. It is also called dyslipidemia, hyperlipidemia, and lipid disorder.
Too much cholesterol in the blood is a major risk for heart disease, which may lead to a heart attack, heart failure (not being able to pump enough blood to the body), and death. igh cholesterol levels are also a risk factor for stroke (a lack of blood and oxygen to the brain), which causes nerve damage.
Cholesterol is a soft, waxy, fat-like substance found in the bloodstream and cells of the body. Cholesterol synthesis is a naturally occurring process that functions to produce membranes for all cells in the body, including those in the brain, nerves, muscles, skin, liver, intestines, and heart. Cholesterol is also converted into steroid hormones, such as androgens and estrogens (the male and female sex hormones) and the adrenal hormones (cortisol, corticosterone, and aldosterone). In the liver, cholesterol is the precursor to bile acids that aid in the digestion of food, especially fats. Cholesterol is also used in making vitamin D.
The body obtains cholesterol in two ways, producing the majority of it in the body and consuming the rest in the diet in the form of animal products, such as meats, poultry, fish, eggs, butter, cheese, and whole milk. Plant foods, like fruits, vegetables, and grains, do not contain cholesterol. Fat that occurs naturally contains varying amounts of saturated and unsaturated fat.
High cholesterol can cause the formation and accumulation of plaque deposits in the arteries. Plaque is composed of cholesterol, other fatty substances, fibrous tissue, and calcium, normal substances in the blood that become deposited on the artery walls if the blood does not flow properly. When plaque builds up in the arteries, it results in atherosclerosis (hardening of the arteries) or coronary heart disease (CHD). Atherosclerosis can lead to plaque ruptures and blockages in the arteries, which increase the risk for heart attack, stroke, and death, as well as circulation problems, such as Raynaud's disease and high blood pressure.
The development of plaques and blockages in the arteries involves several steps. When the endothelium (the innermost lining of the arteries) is damaged by oxidation, cholesterol particles, proteins, and other substances are deposited into the damaged wall and form plaques. More cholesterol and other substances are incorporated into the plaque, and the plaque grows, narrowing the artery. Over time, plaque deposits may grow large enough to interfere with blood flow through the artery (this is called a blockage). When coronary arteries (the arteries supplying the heart with blood) are blocked, angina (chest pain) may occur; when arteries in the legs are blocked, leg pain or cramping may occur; and when arteries supplying the brain with blood are blocked, stroke may occur.
The platelets collecting on the plaque deposit form a clot as they try to rush by but get caught, because the lining of the artery is rough and the platelets are sticky. Then the clot can break off and travel through the body, getting lodged in vessels of the leg or brain and less commonly the lungs. If a plaque ruptures or tears, a thrombus (blood clot) may develop. If a blood clot completely blocks blood flow through a coronary artery, myocardial infarction (heart attack) occurs; if an artery supplying blood to the brain is completely blocked, stroke occurs.
Blood clots (called emboli) can break loose and travel through the bloodstream and lodge in blood vessels in other parts of the body, including the lungs, heart, brain, and legs. A thromboembolus is when the blood clot lodges in vessels.
According to current estimates, 71.3 million people in America have one or more forms of heart disease. High cholesterol affects about 20% of adults over the age of 20 in the United States. The highest prevalence occurs in women between the ages of 65 and 74. The World Health Organization (WHO) reports that high cholesterol contributes to 56% of cases of coronary heart disease worldwide and causes about 4.4 million deaths each year.
Generally, people who live in countries where blood cholesterol levels are lower, such as Japan, have lower rates of heart disease. Countries with very high cholesterol levels, such as Finland, have very high rates of coronary heart disease. However, some populations with similar total cholesterol levels have very different heart disease rates, suggesting that other factors (such as diet, heredity, and smoking) also influence risk for coronary heart disease.
Evidence is accumulating that eating more carbohydrates, especially simpler, more refined carbohydrates such as white breads, sugar, and pasta, may increase levels of triglycerides in the blood, lower high-density lipoprotein (HDL, or "good") cholesterol, and increase low-density lipoprotein (LDL, or "bad") cholesterol. Thus a low-fat diet, which often means a higher carbohydrate intake, may actually be an unhealthy change.
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types of cholesterol
Saturated fats: Saturated fats are solid at room temperature, Foods that contain a high proportion of saturated fat are butter, lard, coconut oil, cottonseed oil and palm oil, dairy products (such as cream and cheese), meat, skin, and some prepared foods. People with diets high in saturated fat are reported to have an increased incidence of atherosclerosis (hardening of the arteries) and coronary heart disease. Saturated fats are popular with manufacturers of processed foods because they are less vulnerable to rancidity and are generally more solid at room temperature than unsaturated fats.
Unsaturated fats: Unsaturated fats are liquid at room temperature. Unsaturated fats include monounsaturated and polyunsaturated fats. Monounsaturated fat remains liquid at room temperature but may start to solidify in the refrigerator. Foods high in monounsaturated fat include olive, peanut, and canola oils. Avocados and most nuts also have high amounts of monounsaturated fat. Polyunsaturated fat is usually liquid at room temperature and in the refrigerator. Foods high in polyunsaturated fats include vegetable oils, such as safflower, corn, sunflower, soy, and cottonseed oils. The use of monounsaturated and polyunsaturated fats instead of saturated fat can help to lower blood cholesterol levels.
fats: Trans-fatty acids (trans fats) are a type of unsaturated fat. Trans fat is formed when liquid vegetable oils go through a chemical process called hydrogenation, in which hydrogen is added to make the oils more solid. Hydrogenated vegetable fats are utilized in food production because they allow longer shelf life and give food desirable taste, shape and texture. Trans fat can be found in shortenings (e.g., Crisco®), margarine, cookies, crackers, snack foods, fried foods (including fried fast food), doughnuts, pastries, baked goods, and other foods processed with partially hydrogenated oils. Some trans fat is found naturally in small amounts in dairy products and some meats. The primary health risk associated with trans fat consumption is an increased risk of coronary heart disease (CHD). Effective January 1, 2006, the U.S. Food and Drug Administration (FDA) requires food companies to list trans fat content separately on the nutrition facts panel of all packaged foods.
Lipoproteins: Cholesterol and other fats cannot dissolve in the blood. They have to be transported to and from the cells by special carriers called lipoproteins. There are two main types of lipoproteins, including low-density lipoprotein (LDL, or "bad") cholesterol and high-density lipoprotein (HDL, or "good") cholesterol. Another type, very-low-density lipoprotein (VLDL) is converted to LDL in the bloodstream. Each form of lipoprotein contains a specific combination of cholesterol, protein, and triglyceride (a blood fat). VLDL cholesterol contains the highest amount of triglyceride.
Too much LDL cholesterol can block the arteries, increasing the risk of heart attack and stroke. LDL takes cholesterol into the bloodstream, and HDL takes it back to the liver for storage. It is also believed that HDL removes excess cholesterol from plaque in arteries, thus slowing the buildup. Studies suggest that high levels of HDL cholesterol reduce the risk of heart attack.
Lipoprotein (a) (Lp(a)) cholesterol: Lp(a) is a lipoprotein (fat-protein molecule) found in the body that is a genetic variation of LDL cholesterol. A high level of Lp(a) is an important risk factor for developing fatty deposits in arteries. The way increased Lp(a) contributes to disease is not understood, but Lp(a) may attract substances that increase inflammation, such as interleukins (IL-1, IL-6, TNF-alpha) and prostaglandins (PG2), leading to the buildup of fatty deposits.
Triglycerides: Triglycerides are the body's storage form for fat. Most triglycerides are found in adipose (fat) tissue. Some triglycerides circulate in the blood to provide fuel for muscles to work. Extra triglycerides are found in the blood after eating a meal, when fat is being sent from the intestines to fat tissue for storage. People with high triglyceride levels often have high LDL cholesterol and low HDL cholesterol levels. Many people with heart disease also have high triglyceride levels. People with diabetes or who are overweight are also likely to have high triglyceride levels.