Cholesterol

Cholesterol is a fat-soluble steroid alcohol that is produced in the liver from saturated fats and obtained from animal fats and oils in the diet.

Cholesterol is always present in the blood and all cells of the body. Small amounts of cholesterol are required for producing hormones, vitamin D, and bile, and as parts of cell membranes and myelin, the sheaths surrounding nerves. The liver produces about 1,000 mg of cholesterol daily—enough to meet these requirements. Cholesterol is also obtained from animal products in the diet, including meat, fish, shellfish, egg yolks, and dairy products. The amount of cholesterol eaten should be part of a balanced diet, for example, through eating lean meats.

Because cholesterol is not soluble in blood, it is moved through the circulatory system by carrier molecules called lipoproteins—low-density lipoprotein (LDL) and high-density lipoprotein (HDL). LDL has a high proportion of cholesterol. HDL is primarily protein with small amounts of triglycerides and cholesterol.

Most cholesterol in the body is in the form of LDL, which is loaded up with cholesterol in the liver. Excess LDL cholesterol can accumulate on the walls of arteries forming a plaque. Free radicals can oxidize LDL cholesterol, further contributing to plaque formation and atherosclerosis, or “hardening of the arteries.” Plaque narrows the arteries and reduces blood flow. In addition, when pieces of plaque break open, they can initiate the formation of blood clots. Plaque or a clot blocking a coronary artery that carries blood to the heart can cause a heart attack. Blocking an artery that carries blood to the brain can cause a stroke. The higher the LDL cholesterol level, the greater the risk of heart disease and heart attack.

HDL appears to carry excess LDL cholesterol away from the walls of the arteries to the liver, where it can be processed and removed from the body. Thus, high levels of HDL help protect against heart disease, heart attack, and stroke, whereas low levels increase the risk of heart disease. Low HDL levels (below 40 mg/dL for men or 50 mg/dL for women) increase risk for type 2 diabetes.

Risk factors for high LDL cholesterol include:

As women and men get older, their cholesterol levels rise, and the risk of elevated levels increases after the age of 45. Before the age of menopause, women tend to have lower cholesterol levels than men of the same age. After menopause, women's LDL levels tend to rise. High total cholesterol approximately doubles one's risk of heart disease, the number one cause of death among Americans. Every year, more than 1 million Americans have a heart attack and about 500,000 die of heart disease. A 2016 report showed, however, that cholesterol levels of Americans were declining. In a study of nearly 40,000 adults, researchers noted that average total cholesterol decreased from 204 mg/dL to 189 mg/dL between 2000 and 2014. They suggested the reason could be better awareness and control of trans fats in food.

High LDL or low HDL cholesterol levels have no apparent symptoms, at least until complications such as heart disease develop. Therefore, a simple blood test is used to determine cholesterol levels.

Blood tests for cholesterol are usually part of routine physical examinations by general practitioners or family practice physicians. A lipid panel measures total cholesterol, LDL, HDL, and triglycerides in the blood. A lipid panel is inexpensive and routinely covered by health insurance and health maintenance organization plans, including Medicare. Home cholesterol testing kits are available over the counter. Although a desirable total cholesterol level (LDL plus HDL) is below 200 mg/dL, the relative levels of LDL and HDL are important, as are other risk factors, including age, smoking, alcohol consumption, hypertension (high blood pressure), heart disease, or a family history of heart disease.

Treatment for high cholesterol usually begins with lifestyle changes. If a patient has heart disease or additional risk factors in addition to high cholesterol, prescribed lifestyle changes may be augmented with drug therapy.

The primary treatments for high cholesterol are diet, exercise, weight loss, and smoking cessation. This includes limiting daily calories from fat (particularly saturated and trans fats), watching sugar, sodium, and total calorie intake, and eating plenty of healthy foods such as fruits, vegetables, and whole grains. Further, regular exercise and weight control can keep cholesterol in check for many people at low or moderate risk for high cholesterol.

Because most cholesterol comes from eating animal products, a vegetarian or vegan diet can help lower cholesterol. Vegetarians typically consume up to 50% less cholesterol and up to 100% more fiber than people who eat meat. A low-cholesterol vegetarian diet typically consists of at least six servings of whole-grain foods, three or more servings of green leafy vegetables, two to four servings of fruit, two to four servings of legumes, and one or two servings of fat-free dairy products daily. Although newer guidelines place less emphasis on cholesterol numbers in foods eaten, it still is important to lower the amount of saturated and trans fats eaten to keep cholesterol in check.

Exercise helps lower LDL cholesterol and raise HDL cholesterol. Although any amount of regular exercise is helpful, especially for overweight individuals, at least 30 minutes of vigorous aerobic exercise—such as fast walking, bicycling, jogging, roller skating, swimming, or stair-climbing, at least three times a week may help lower cholesterol. By including gentle exercise as part of their regular daily routine, physically inactive people can gradually work up to more vigorous, sustained exercise. Studies have shown that yoga can help lower high cholesterol, as well as reduce high blood pressure. Studies also have shown that moderate strength or resistance training, as well as other types of exercise, can lead to significant improvements in cholesterol metabolism, reducing total cholesterol and triglycerides, and raising HDL levels in the blood.

Although a variety of drugs can be prescribed for reducing cholesterol levels, to be effective, they must be accompanied by lifestyle changes, especially exercise and diet. Typically, only people with LDL cholesterol higher than 70 mg/dL who also have a 7.5% risk of heart attack or stroke, those with very high LDL levels (190 mg/dL or higher), and people with a history of heart disease or diabetes need cholesterol-lowering drugs. Cholesterol-lowering drugs also have side effects that make them unsuitable for some people.

Statins are the most frequently prescribed class of cholesterol-lowering drugs. They lower LDL by slowing the body's production of cholesterol. Statins have shown to be of benefit as both a primary and secondary course of prevention. However, they are best used alongside dietary changes as a mechanism to lower LDL cholesterol. At high doses, some statins have been shown to cause side effects. Examples of statins include atorvastatin (Lipitor), fluvastatin (Lescol), lovastatin (Mevacor, Altoprev), pravastatin (Pravachol), and simvastatin (Zocor).

Bile-acid sequestrants, also called resins, increase the amount of bile excreted in feces. This forces the liver to make more bile, thereby utilizing more cholesterol so that less is available to enter the bloodstream. Bile-acid sequestrants are prescribed along with other cholesterol-lowering drugs, such as statins. Examples include cholestyramine (Prevalite, Questran), colesevelam (Welchol), and colestipol (Colestid).

Cholesterol absorption inhibitors reduce the amount of cholesterol absorbed from food in the intestine. An example is ezetimibe (Zetia).

Fibrates or fibric-acid derivatives primarily lower triglycerides but also can increase HDL cholesterol. They are normally used in combination with other cholesterol-lowering drugs. Examples of fibrates include gemfibrozil (Loprid), clofibrate (Atromid-S), and fenofibrate (Tricor). Niacin (nicotinic acid) affects how the liver produces fat in the blood. Although it can be purchased with or without a prescription, it should be used only under the supervision or a physician.

Dietary supplements or alternatives for lowering cholesterol include niacin, nuts, quorn, and soy. Foods high in omega-3 fatty acids, such as fish oil, are dietary supplements designed to lower triglyceride levels.

In addition to exercise and diet, some alternative practitioners recommend herbal supplements to reduce cholesterol levels. Using any herbal remedy or alternative therapy, however, should be discussed with a physician, because the remedies can interact negatively with some prescription medications.

According to the National Center for Complementary and Alternative Medicine (NCCAM), several studies have shown short-term (up to three-month) reductions in total blood cholesterol levels with garlic (standardized dehydrated tablets, aged garlic extract, oil macerates, distillates, raw garlic). These reductions have not been observed in longer-term (six-month) studies. Although green tea is sometimes recommended for lowering LDL, the NCCAM has reported that there is too little reliable data to evaluate this claim. Likewise, there is little evidence that phytoestrogen supplements such as red clover, grapeseed extract, flaxseed oil, or blue-green algae affect cholesterol levels.

High cholesterol is a major risk factor for cardiovascular disease. Left untreated, high LDL cholesterol can clog blood vessels, leading to chest pain (angina), blood clots, and heart attacks. Reducing LDL cholesterol levels may slow or reverse cholesterol build-up in arteries and help prevent future heart attacks and stroke, prolong life, and improve the quality of life in patients with cardiovascular disease.

The American Heart Association recommends that all adults have their cholesterol levels checked every four to six years. A low-fat (particularly saturated fat), low-cholesterol, high-fiber diet and regular exercise are the best means of controlling cholesterol levels and reducing the risk of heart disease. Maintaining a healthy weight, limiting alcohol consumption, and not smoking can also help control cholesterol. For people with cardiovascular disease or at high risk for heart disease, including those over age 45, diabetes patients, and those with a family history of heart disease, cholesterol-lowering medications might be effective. It remains unclear, however, whether cholesterol-lowering drugs benefit otherwise healthy people with only a low-to-moderate risk for heart disease. For these people, exercise and a low-fat diet may be just as effective as statin drugs.

See also Exercise ; Obesity ; Weight loss .