Hyperlipidemia, also known as high cholesterol, hyperlipoproteinemia, or dyslipidemia, is a high level of lipids (fats) in the bloodstream. These lipids include cholesterol, cholesterol compounds, phospholipids, and triglycerides, all carried in the blood as part of large molecules called lipoproteins.
Hyperlipidemia affects the way lipids are produced, used, carried in the blood, and disposed of by the body. The three types of hyperlipidemia include:
The lipoproteins present in blood plasma that transport lipids belong to the following major groups:
People with hyperlipidemia are thought to be more likely to develop heart disease. When individuals have too much cholesterol in the blood, the cholestrol accumulates in arteries, which can lead to their narrowing (atherosclerosis) and, cause heart disease or stroke.
Generally speaking, doctors recommend that LDL levels be low and HDL high. HDL is often called “good cholesterol” and LDL “bad cholesterol,” although this is misleading because neither HDL nor LDL is in fact cholesterol; they are both lipoproteins that transport cholesterol in the blood.
According to the Centers for Disease Control and Prevention (CDC), from 2011 to 2012 approximately 37% of the adult population had LDL levels in the range at which experts recommend cholesterol medication. Nearly 29 million people had total cholesterol levels greater than 240 mg/dl.
High cholesterol by itself does not cause symptoms, so people are generally not aware that their lipid levels are too high.
Simple blood tests are done to check blood lipid levels. The CDC recommends that people have their cholesterol checked every four to six years after age 20. A lipoprotein test, also called a fasting lipid test, is commonly performed as part of a routine medical examination. The test measures lipid levels and usually reports on four groups:
A total cholesterol value greater than 200 mg/dL is believed to indicate a greater risk for heart disease. A high HDL is desirable, as are low triglycerides. Cardiologists have believed that LDL levels are a better predictor of heart disease, and they determine how your high cholesterol should be treated, although guidelines issued in 2013 shifted focus from LDL to a more comprehensive picture of lifestyle factors, including weight and blood pressure. In the late 2010s, the importance of non-HDL cholesterol as a marker of risk was also noted. This considers other parts of ‘bad’ cholesterol known as IDL, VLDL and lipoprotein(a) as well as LDL-cholesterol.
The ratio of triglycerides to HDL is another marker used to identify risk of heart attack or stroke. The lower the ratio, the better. A TG/HDL ratio less than 2 is ideal. A ratio over 4 has been shown to be a good predictor of developing coronary artery disease and of insulin resistance. It also predicts worse outcomes after acute ischaemic stroke.
In recent years, much more complex cholesterol tests have been developed, which can break down the LDL component into particle sizes, leading to some refinement of analysis of cholesterol levels. Small LDL particles are believed to present an actual risk, whereas large, fluffy LDL particles are protective and associated with low triglycerides. It is possible to have low LDL numbers and yet have a high level of small, dangerous particles. Some experts now believe that testing for LDL-P and apolipoprotein B (apoB) with a test called the NMR test would be a better approach for deciding treatments.
Treatment depends on lipid levels, the presence of risk factors for heart disease, and general health. When lipid levels are not balanced, the goal is to bring them under control, and this is done by changing dietary habits. A patient with hyperlipidemia may be given dietary advice such as:
If dietary changes do not correct the hyperlipidemia, a doctor may recommend a course of drug therapy. In the Unites States, men older than age 35 and postmenopausal women are generally candidates for lipid-lowering medications.
To treat hyperlipidemia, a diet low in total fat, saturated fat, and cholesterol is recommended, along with reducing or avoiding alcohol intake and losing weight. The American Heart Association (AHA) endorses the following dietary recommendations for people with high blood cholesterol:
Categories of appropriate foods include:
These recommendations translate into the following practical dietary guidelines:
Although lowering fat intake is commonly recommended, particularly for those who need to lose weight, it is now recognised that some types of fat and carbohydrates are key to the maintenance of a healthy lipid profile. Replacement of saturated fat with unsaturated fats (monounsaturates and polyunsaturates) and/or high fiber, complex carbohydrates (e.g., whole grain foods) can lower blood cholesterol levels. Diets high in refined carbohydrates or sugar and/or saturated fat are associated with increases in cholesterol and triglyceride levels.
The AHA states that, under current guidelines, drug therapy is considered for:
There are several types of drugs available to help lower blood cholesterol levels, and they work in different ways. Some are better at lowering LDL cholesterol, some are good at lowering triglycerides, and others help raise HDL cholesterol. Lipid-lowering medications include:
Doctors have prescribed cholesterol-lowering medications such as statins since the 1980s. Studies have regularly shown a reduction in risk of cardiovascular events with their use. A review of 90,000 statin users by the Medical Research Council in Oxford and the University of Sydney concluded that risk of fatal heart attack or stroke fell by about a third. Changes in recommendations have steadily increased the number of people taking them. In 2016, the U.S. Preventive Services Task Force issued guidelines increasing the number of people who should be screened to see if they could benefit from stains, regardless of whether they have a history of heart disease. A 2017 study concluded that treating asymptomatic people with statins could prevent heart attacks.
There is not universal acceptance of the value of cholesterol-reducing drugs. Some cardiologists worry about the side effects of statins, which can include muscle pain and cognitive disruptions. Others worry that statin research and advertising focuses on relative risk as opposed to absolute risk of heart attacks, allowing much greater claims of effectiveness than are actually the case. They argue that statins are only effective in men who have had a prior heart attack and that they have never been proven effective at reducing heart attacks in women because they have not been as well represented in studies to date. More research is needed to look at their effects on women of moderate risk.
Prognosis depends on the presence of any additional risk factors for heart disease, such as diabetes, high blood pressure, being a male over age 45 or a female over age 55, and having a first-degree female relative diagnosed with heart disease before age 65 or a first-degree male relative diagnosed before age 55 and with obesity. Outcome is also highly related to early diagnosis, treatment, and compliance with therapy.
Hyperlipidemia can be prevented by eating a healthy diet, maintaining a normal weight, and being physically active. Everyone can take steps to maintain proper cholesterol levels, although some people have a genetic predisposition to high cholesterol levels. The most important considerations are to eat foods that are low in saturated fat, to exercise regularly, to lose weight if overweight, to avoid smoking, and to get routine medical examinations and cholesterol tests.
See also Coronary heart disease ; Dietary cholesterol ; Fats ; High-fat, low-carb diets ; Triglycerides .
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Monique Laberge, PhD
Revised by Amy Hackney Blackwell, PhD