High cholesterol
High cholesterol, also called Hypercholesterolemia, is the presence of high levels of cholesterol in the blood. It is a form of hyperlipidemia, hyperlipoproteinemia, and dyslipidemia.
Elevated levels of non-HDL cholesterol and LDL in the blood may be a consequence of diet, obesity, inherited diseases, or the presence of other diseases such as type 2 diabetes and an underactive thyroid.
Cholesterol is one of three major classes of lipids produced and used by all animal cells to form membranes. Plant cells manufacture phytosterols but in small quantities. Cholesterol is the precursor of the steroid hormones and bile acids. Since cholesterol is insoluble in water, it is transported in the blood plasma within protein particles. Lipoproteins are classified by their density: very low density lipoprotein, intermediate density lipoprotein, low density lipoprotein and high density lipoprotein. All the lipoproteins carry cholesterol, but elevated levels of the lipoproteins other than HDL, particularly LDL-cholesterol, are associated with an increased risk of atherosclerosis and coronary heart disease. In contrast, higher HDL cholesterol levels are protective.
Avoiding trans fats and replacing saturated fats in adult diets with polyunsaturated fats are recommended dietary measures to reduce total blood cholesterol and LDL in adults. In people with very high cholesterol, diet is often not sufficient to achieve the desired lowering of LDL, and lipid-lowering medications are usually required. If necessary, other treatments such as LDL apheresis or even surgery are performed. About 34 million adults in the United States have high blood cholesterol.
Signs and symptoms
Although hypercholesterolemia itself is asymptomatic, longstanding elevation of serum cholesterol can lead to atherosclerosis. Over decades, elevated serum cholesterol contributes to the formation of atheromatous plaques in the arteries. This can lead to progressive narrowing of the involved arteries. Alternatively, smaller plaques may rupture and cause a clot to form and obstruct blood flow. A sudden blockage of a coronary artery may result in a heart attack. A blockage of an artery supplying the brain can cause a stroke. If the development of the stenosis or occlusion is gradual, the blood supply to the tissues and organs slowly diminishes until organ function becomes impaired. At this point tissue ischemia may manifest as specific symptoms. For example, temporary ischemia of the brain may manifest as temporary loss of vision, dizziness and impairment of balance, difficulty speaking, weakness or numbness or tingling, usually on one side of the body. Insufficient blood supply to the heart may cause chest pain, and ischemia of the eye may manifest as transient visual loss in one eye. Insufficient blood supply to the legs may manifest as calf pain when walking, while in the intestines it may present as abdominal pain after eating a meal.Some types of hypercholesterolemia lead to specific physical findings. For example, familial hypercholesterolemia may be associated with xanthelasma palpebrarum, arcus senilis, and xanthomata of the tendons, especially of the fingers. Type III hyperlipidemia may be associated with xanthomata of the palms, knees and elbows.
Causes
Hypercholesterolemia is typically due to a combination of environmental and genetic factors. Environmental factors include weight, diet, and stress. Loneliness is also a risk factor.Diet
Diet affects blood cholesterol, but the size of this effect varies between individuals.A diet high in sugar or saturated fats increases total cholesterol and LDL. Trans fats have been shown to reduce levels of high-density lipoprotein while increasing levels of LDL.
A 2016 review found tentative evidence that dietary cholesterol is associated with higher blood cholesterol. As of 2018 there appears to be a modest positive, dose-related relationship between cholesterol intake and LDL cholesterol.
Medical conditions and treatments
A number of other conditions can also increase cholesterol levels including diabetes mellitus type 2, obesity, alcohol use, monoclonal gammopathy, dialysis therapy, nephrotic syndrome, hypothyroidism, Cushing's syndrome and anorexia nervosa. Several medications and classes of medications may interfere with lipid metabolism: thiazide diuretics, ciclosporin, glucocorticoids, beta blockers, retinoic acid, antipsychotics, certain anticonvulsants and medications for HIV as well as interferons.Genetics
Genetic contributions typically arise from the combined effects of multiple genes, known as "polygenic", although in certain cases, they may stem from a single gene defect, as seen in familial hypercholesterolemia. In familial hypercholesterolemia, mutations may be present in the APOB gene, the autosomal recessive LDLRAP1 gene, autosomal dominant familial hypercholesterolemia variant of the PCSK9 gene, or the LDL receptor gene. Familial hypercholesterolemia affects about one in 250 individuals.The Lithuanian Jewish population may exhibit a genetic founder effect. One variation, G197del LDLR which is implicated in familial hypercholesterolemia, has been dated to the 14th century. The of these variations has been the subject of debate.
Diagnosis
| Cholesterol type | mmol/L | mg/dL | Interpretation |
| total cholesterol | <5.2 | <200 | Desirable |
| total cholesterol | 5.2–6.2 | 200–239 | Borderline |
| total cholesterol | >6.2 | >240 | High |
| LDL cholesterol | <2.6 | <100 | Most desirable |
| LDL cholesterol | 2.6–3.3 | 100–129 | Good |
| LDL cholesterol | 3.4–4.1 | 130–159 | Borderline high |
| LDL cholesterol | 4.1–4.9 | 160–189 | High and undesirable |
| LDL cholesterol | >4.9 | >190 | Very high |
| HDL cholesterol | <1.0 | <40 | Undesirable; risk increased |
| HDL cholesterol | 1.0–1.5 | 41–59 | Okay, but not optimal |
| HDL cholesterol | >1.55 | >60 | Good; risk lowered |
Cholesterol is measured in milligrams per deciliter of blood in the United States and some other countries. In the United Kingdom, most European countries, and Canada, millimoles per liter of blood is the measure.
For healthy adults, the UK National Health Service recommends upper limits of total cholesterol of 5 mmol/L, and low-density lipoprotein cholesterol of 3 mmol/L. For people at high risk of cardiovascular disease, the recommended limit for total cholesterol is 4 mmol/L, and 2 mmol/L for LDL.
In the United States, the National Heart, Lung, and Blood Institute within the National Institutes of Health classifies total cholesterol of less than 200 mg/dL as "desirable", 200 to 239 mg/dL as "borderline high", and 240 mg/dL or more as "high".
There is no absolute cutoff between normal and abnormal cholesterol levels, and values must be considered in relation to other health conditions and risk factors.
Higher levels of total cholesterol increase the risk of cardiovascular disease, particularly coronary heart disease. Levels of LDL or non-HDL cholesterol both predict future coronary heart disease; which is the better predictor is disputed. High levels of small dense LDL may be particularly adverse, although measurement of small dense LDL is not advocated for risk prediction. In the past, LDL and VLDL levels were rarely measured directly due to cost.
Levels of fasting triglycerides were taken as an indicator of VLDL levels, while LDL was usually estimated by the Friedewald formula:
LDL total cholesterol – HDL –.
However, this equation is not valid on nonfasting blood samples or if fasting triglycerides are elevated. Recent guidelines have, therefore, advocated the use of direct methods for the measurement of LDL wherever possible. It may be useful to measure all lipoprotein subfractions when assessing hypercholesterolemia and measurement of apolipoproteins and lipoprotein can also be of value. Genetic screening is now advised if a form of familial hypercholesterolemia is suspected.
Classification
Classically, hypercholesterolemia was categorized by lipoprotein electrophoresis and the Fredrickson classification. Newer methods, such as "lipoprotein subclass analysis", have offered significant improvements in understanding the connection between atherosclerosis progression and clinical consequences. If the hypercholesterolemia is hereditary, more often a family history of premature, earlier onset atherosclerosis is found.Screening method
The U.S. Preventive Services Task Force in 2008 strongly recommended routine screening for men 35 years and older and women 45 years and older for lipid disorders and the treatment of abnormal lipids in people at increased risk of coronary heart disease. They also recommend routinely screening men aged 20 to 35 years and women aged 20 to 45 years if they have other risk factors for coronary heart disease. In 2016 they concluded that testing the general population under the age of 40 without symptoms is of unclear benefit.In Canada, screening is recommended for men 40 and older and women 50 and older. In those with normal cholesterol levels, screening is recommended once every five years. Once people are on a statin further testing provides little benefit except possibly to determine compliance with treatment.
In the UK, after someone is diagnosed with familial hypercholesterolemia, clinicians, family, or both, contact first- and second-degree relatives to come forward for testing and treatment. Research suggests that clinician-only contact results in more people coming forward for testing.