Cholesterol, Other Lipids, and Lipoproteins

Description

An in-depth report on the diagnosis, treatment, and prevention of high cholesterol.

Risk Factors

About half of all American adults, regardless of ethnicity, have total cholesterol levels over 200. Over 25% have been told by doctors that they have unhealthy levels. The major risk factor for these high rates may be the Western lifestyle. The typical high-fat/low-fiber American diet coupled with sedentary habits is largely responsible for this unfortunate trend.

Risk by Gender

Men. Heart disease is the major cause of death in men. On average, men develop coronary artery disease ten to 15 years earlier than women do and their risk for dying of heart disease at younger ages than women is higher.

Women. Coronary artery disease is still the number one killer of women as well. Women between the ages of 20 and 34 and after menopause, around age 55, have higher cholesterol levels than men do. Some evidence suggests HDL levels might have more significance in women than in men. In one study, at total cholesterol levels above 200, women with HDL levels below 50 had a higher death rate than those with levels above 50, regardless of their LDL cholesterol levels. Women also appear to be more susceptible to the high-triglyceride low-HDL syndrome, which may be a particular risk factor for heart disease.

Risk by Age

Children and Adolescents. It is not clear what constitutes normal cholesterol levels in children. According to one study, the current adult guidelines are accurate only for Caucasian adolescent males at age 16. They do not take into account changes in cholesterol levels that occur between the ages of 8 and 18, which, furthermore, may vary between genders and population groups. In general, cholesterol levels tend to naturally rise sharply until puberty, then decrease sharply, and then rise again.

It is increasingly clear, however, that children who are overweight are at higher risk for high triglycerides and low HDL, which many experts now believe may be directly related to later unhealthy cholesterol levels. One 2000 study reported evidence of injuries in the arteries in children aged nine to 11 with high cholesterol levels. A 2003 study confirmed that childhood LDL-C level and body-mass index (BMI) are strongly associated with cardiovascular risk during adulthood.

As in adults, primary source of unhealthy cholesterol levels in children is most likely from diets high in unhealthy fats, saturated fats (found mainly in animal and dairy products) and trans-fatty acids (found in commercial food products). One study reported that five out of six American young people consume too many fats. A certain amount of fat is important for growth, but over-consumption is a major factor in the obesity epidemic occurring in American children as it is in adults. Simply lowering fat intake in their diets may safely reduce cholesterol in young children, according to one long-term study.

Less common causes of unhealthy cholesterol levels in children are the following:

• Low-birth weight (associated with low HDL levels).
• Hypothyroidism.
• Kidney or liver diseases.
• Homozygous familial hypercholesterolemia. This is an uncommon inherited condition that causes severe cholesterol imbalances and can result in very early heart disease.
• Certain medications, such as specific antiseizure agents, corticosteroids, isotretinoin (Accutane).

Young and Middle-Aged Adults. The strongest evidence of unhealthy cholesterol levels and heart disease is in middle-aged adults over 40. Research, however, is now strongly suggesting that the younger a person is unhealthy cholesterol levels develop, the greater the chance for serious heart and blood vessel problems in the future. In one important 2000 study, young men (ages 16 through 34) who had cholesterol levels at or above 240 mg/dL had two to four times the risk of dying from heart attack or other cardiac problems than did men whose cholesterol was lower than 200 mg/dL. Young men without cholesterol problems also had higher life expectancy, by up to eight years. Other studies have suggested similar risks from unhealthy cholesterol in young women as well.

Elderly Adults. The effects of high cholesterol in people over 70 and how to treat them have been controversial issues. A number of studies report that in older adults, high cholesterol levels pose a significant risk for death from coronary artery disease, while some others have suggested that lowering cholesterol levels in the elderly may increase the risk for stroke or heart attack. (For example, a 2001 study reported that statin therapy reduces mortality rates in people over 65 with heart disease.) According to 2000 data, men older than 70 with levels under 160 mg/dL or more than 240 mg/dL were at significant risk for serious heart events. Some experts, then, now suggest that the ideal cholesterol range for older adults may be between 200 and 219 mg/dL.

Obesity, Metabolic Syndrome, and Type 2 Diabetes

In American obesity is at epidemic levels in all age groups. The effect of obesity on cholesterol levels is complex. Although obesity does not appear to be strongly associated with overall cholesterol levels, among obese individuals triglyceride levels are usually high while HDL (beneficial cholesterol) levels tend to be low, both risk factors for heart disease. Obesity, in any case, has other effects (hypertension, increase in inflammation) that pose major risks to the heart.

Obesity is a particularly hazard when it is one of the components of the metabolic syndrome, also called syndrome X. This syndrome consists of obesity marked by abdominal fat, unhealthy cholesterol levels, high blood pressure, and insulin resistance. Metabolic syndrome is a pre-diabetic condition that is significantly associated with heart disease and higher mortality rates from all causes. A 2002 study estimated that 24% of the population now has this condition.

Obesity is highly linked with type 2 diabetes, in any case. And diabetes itself poses a significant risk for high cholesterol levels and heart disease.

Hypothyroidism

Hypothyroidism is significantly associated with unhealthy lipid levels. (Lipids are fat molecules). Specifically, people with hypothyroidism and even subclinical hypothyroidism are at higher risk for high total and LDL -- the so-called bad -- cholesterol, triglycerides, and other lipids associated with heart disease. In fact, one 2000 study indicated that hypothyroidism is second only to poor dietary habits as a cause of high unhealthy cholesterol levels. Treating the thyroid condition can significantly reduce cholesterol levels. Among people with high cholesterol levels, between 1.3% and 2.8% have hypothyroidism and between 4.4% and 11.2% have subclinical hypothyroidism. Some experts are suggesting then that patients with high cholesterol should be assessed for thyroid function before they are given cholesterol-lowering agents. Research on whether the association between mild hypothyroidism and cholesterol levels has any significance is mixed, however.

Hypothyroidism is a decreased activity of the thyroid gland which may affect all body functions. The rate of metabolism slows causing mental and physical sluggishness. The most severe form of hypothyroidism is myxedema, which is a medical emergency.

Genetic Factors and Family History

Genetics play a major role in determining a person's blood cholesterol levels, and children from families with a history of premature heart disease should be tested for cholesterol levels after age two. Genes may influence whether one has low HDL levels, high LDL levels, triglycerides, or high levels of other lipoproteins, such as lipoprotein(a).

Some inherited disorders and genetic abnormalities have been identified:

• Familial hypercholesterolemia causes hazardous elevations of cholesterol. It may be more common than thought; one European study reported familial hypercholesterolemia in one out of 400 people.
• Familial lipoprotein lipase deficiency is a very rare disorder that causes depletion of lipoprotein lipase. This is an enzyme that appears to be important in the removal of lipoproteins that are rich in triglycerides. People who are deficient in it have high levels of cholesterol and fat in their blood. A very low-fat diet is essential and is an effective treatment for these individuals.
• Two studies have found a genetic mutation affecting neuropeptide Y in people with high total cholesterol and LDL levels. Neuropeptide Y is a compound in the brain that regulates appetite.
• Researchers have identified a gene called APOAV, which may help detect patients at risk for elevated levels of triglycerides.

Other Medical Conditions

Other medical conditions strongly associated with unhealthy cholesterol levels are the following:

• Polycystic ovarian syndrome. Women with this disorder, particularly those who are obese, appear to be at increased risk for high triglyceride and low HDL levels. This risk may be due to higher levels of the male hormone testosterone in these women.

Click the icon to see an image of a polycystic ovary.

• Kidney disease.