Cholesterol is a waxy fat (lipid) that is present in all human beings. In modest amounts, cholesterol is necessary for good health. However, unhealthy levels of cholesterol are directly linked to hardening of the arteries (atherosclerosis), coronary artery disease, stroke and other cardiovascular conditions.
Keeping cholesterol levels healthy is especially important for people with diabetes because cardiovascular diseases are their leading cause of death. According to the American Diabetes Association, heart and other cardiovascular diseases occurs earlier and two to four more times more often in people with diabetes than in the general population.
The liver makes 80 percent of the body’s cholesterol. The rest is ingested from animal products such as meat, eggs and dairy foods. There are several forms of cholesterol, but the two most common types are low-density lipoproteins (LDL or “bad” cholesterol) and high-density lipoproteins (HDL or “good” cholesterol). Levels of other blood fats, including triglycerides, should also be watched closely. As with cholesterol, excess triglycerides are linked to heart disease and other cardiovascular disorders.
Cholesterol guidelines, like those regarding high blood pressure, are stricter for individuals with diabetes. The ADA generally advises people with diabetes to maintain cholesterol levels as follows, with measurements in milligrams per deciliter (mg/dL):
|LDL||< 100 mg/dL||< 100 mg/dL|
|HDL||> 45 mg/dL||> 55 mg/dL|
|Triglycerides||< 150 mg/dL||< 150 mg/dL|
The National Cholesterol Education Program recommends total cholesterol levels of less than 200 mg/dL. These levels are diagnosed with a simple cholesterol blood test.
Two of the most important lifestyle changes to lower cholesterol, a nutritious diet and exercise, also help in controlling glucose (blood sugar). However, abnormal cholesterol levels can be difficult to manage and may require treatment with cholesterol-reducing drugs.
About cholesterol and diabetes
Cholesterol is a fat-like substance (lipid) that all humans naturally produce. It provides many benefits to the body, including helping to build and repair cell membranes, and providing a starting point in the formation of hormones such as estrogen and testosterone.
However, abnormal cholesterol levels can build up and form plaque within the arteries, leading to heart and blood vessel disease. People with diabetes are particularly vulnerable to heart disease and stroke, which are the leading causes of death from diabetes, according to the American Diabetes Association (ADA).
In general, people with diabetes can reduce their risk of health problems by maintaining the following cholesterol levels, according to the ADA (all measurements are in milligrams per deciliter, mg/dL):
|LDL||< 100 mg/dL||< 100 mg/dL|
|HDL||> 45 mg/dL||> 55 mg/dL|
|Triglycerides||<150 mg/dL||< 150 mg/dL|
The National Cholesterol Education Program recommends total cholesterol levels of less than 200 mg/dL.
Recent research emphasizes the importance of having adequate HDL as well as lowering harmful blood fats. Cholesterol ratio is a person’s total cholesterol divided by HDL number. According to the American Heart Association, the level of total cholesterol should not be more than five times the level of good cholesterol. This may be expressed as the ratio 5:1. A ratio of 3.5:1 is considered optimal.
Target cholesterol levels for people with diabetes are more stringent than for those without diabetes. In addition, diabetic individuals often have additional risk factors for coronary artery disease, such as high blood pressure and family history, and may be treated earlier and more aggressively than patients without these risk factors.
Lipoproteins carry most of the cholesterol in the bloodstream, and they behave very differently as they move through the body:
- High-density lipoproteins (HDLs). “Good” cholesterol, HDLs move easily through the blood and are actually beneficial to the body. They are stable and do not stick to artery walls. They help prevent atherosclerosis by carrying cholesterol away from the arteries and back to the liver, where the process of its removal from the body begins. Liver damage, from fatty liver disease (a common disorder in people with type 2 diabetes), alcohol abuse or other conditions, can undo the beneficial effects of HDLs.
- Low-density lipoproteins (LDLs). “Bad” cholesterol, LDLs contain more fat and less protein than HDLs. LDLs are unstable; they tend to fall apart. Rather than being removed from the body by the liver, they stick to, and can damage, cells lining the inside of artery walls.
Areas of cell damage provide a magnet-like attraction for other fatty substances (e.g., triglycerides), sticky blood-clotting materials (e.g., fibrin and platelets) and white blood cells. The waxy accumulation of these materials is known as plaque. This can eventually lead to atherosclerosis or coronary artery disease. Therefore, high levels of LDLs are strongly associated with increased risk for heart disease. Many people with high levels of “bad” cholesterol also have high triglyceride levels because both types of fats have similar risk factors (e.g., obesity and diabetes).
- Very-low-density lipoproteins (VLDLs). Associated with “very bad” cholesterol, VLDLs and so-called intermediate-density lipoproteins (IDLs) belong to a newer category known as non-HDL cholesterol. Studies are showing that high levels of non-HDLs can raise the risk of nonfatal heart attack and angina (cardiac chest pain) among individuals who already have heart disease.
- Chylomicrons. These large particles carry a small percentage of cholesterol but are rich in triglycerides.
- Remnant-like particle cholesterol (RLP-C). Increased levels are seen in people with coronary artery disease as well as individuals with normal cholesterol levels, and are linked to lipid accumulation. There are no known dietary interventions at this time. Lipid-lowering therapy is the recommendation to decrease RLP-C levels.
People with unhealthy levels of cholesterol are at risk for cardiovascular disease, which tends to occur earlier and two to four times more often than in people without diabetes, according to the ADA. It is also more often fatal. Diabetes increases these risks for a number of reasons:
- High blood pressure and diabetes are linked in many ways. More than 60 percent of adults with diabetes have high blood pressure, according to the ADA. Complications such as diabetic nephropathy and diabetic retinopathy can also involve high blood pressure. In addition, high blood pressure, insulin resistance and unhealthy levels of blood fats occur together (metabolic syndrome).
- High glucose (blood sugar) levels damage blood vessels by making the walls thicker and less elastic.
- Glucose frequently latches onto lipoproteins, which tend to stay in the bloodstream longer when they are sugar-coated.
- Diabetic patients often have low levels of HDL cholesterol and high levels of triglycerides. These factors in combination increase the risk of cardiovascular disease.
Like cholesterol, triglycerides are common types of fats (lipids) that are essential for good health when present in normal amounts. They account for about 95 percent of the body’s fatty tissue. Triglycerides are present in food and are manufactured by the body.
Abnormally high triglyceride levels are associated with a number of diseases and conditions, such as cirrhosis (a disease of the liver), underactive thyroid (hypothyroidism), inflammation of the pancreas (pancreatitis) and poorly controlled diabetes.
High triglyceride levels are also associated with known risk factors for heart disease, such as low levels of HDL (“good”) cholesterol, high levels of LDL (“bad”) cholesterol and obesity. Triglycerides may also contribute to a type of thickening of artery walls – a physical change believed to be a predictor of hardening of the arteries (atherosclerosis). Researchers are continuing to investigate exactly how triglycerides affect cardiovascular health.
Triglyceride-lowering medications include fibrates and niacin. They reduce the production of triglycerides and remove triglycerides from the system.
The American Diabetes Association recommends that people with diabetes maintain triglyceride levels below 150 milligrams per deciliter (mg/dL).
About high cholesterol
The cholesterol value in the human body can rise to abnormally high levels when someone eats a diet high in saturated fats or trans fats – especially when that person is obese or rarely exercises (even moderate exercise benefits the heart).
Unhealthy levels of cholesterol are dangerous because they are linked directly to coronary artery disease and hardening of the arteries (atherosclerosis). Abnormal cholesterol levels have also been linked to the risk of heart attack and stroke. Researchers have developed guidelines to help patients understand their risk of heart attack. These guidelines are based on known risk factors, such as diabetes, smoking and obesity.
Studies have shown that cholesterol levels are linked to dietary fat. In particular, artificial trans fats are especially dangerous. Manufactured trans fats not only increase levels of “bad” LDL cholesterol, but also decrease “good” HDL cholesterol. This is especially worrisome, because artificial trans fats (which prolong the shelf life of processed foods) are common ingredients in potato chips and other snack foods, many types of margarine and shortening, and deep-fried and fast foods. The U.S. Food and Drug Administration (FDA) now requires that processed foods list levels of trans fatty acid. This is in addition to other nutritional information on labels.
Diet and other lifestyle changes often have a powerful effect in helping to normalize cholesterol levels. However, medication may sometimes be necessary to bring cholesterol levels under control.
Treatment and prevention of high cholesterol
Patients with diabetes have the same treatment and prevention options available to them as the general population. There are several steps that diabetic patients can take to monitor and control their cholesterol levels. These include:
- Regular cholesterol screenings. The National Cholesterol Education Program recommends that males and females 20 years of age and older have a lipid profile (cholesterol test) every five years. Regular cholesterol screenings are particularly important for people who have risk factors such as diabetes, obesity or a family history of cardiovascular disease. These higher-risk individuals, and people over age 65, may be screened more frequently.
The American Diabetes Association (ADA) advises that adults with diabetes maintain levels of LDL cholesterol less than 100 milligrams per deciliter (mg/dL) and HDL cholesterol of more than 40 mg/dL for men and more than 50 mg/dL for women. In addition, the ADA recommends that adults keep their triglyceride levels below 150 mg/dL.
Children with diabetes require cholesterol screening after 2 years of age if they have a family history of high cholesterol. Children with no family history of high cholesterol should have cholesterol screening at puberty, and the test should be repeated every five years.
Cholesterol screening is fast and relatively painless. Regular screenings are essential for the prevention and treatment of high cholesterol.
- Blood pressure management. High blood pressure (hypertension) is a risk factor for diabetes and for coronary artery disease. People with diabetes should take appropriate precautions to reduce their risk becoming hypertensive or to manage their high blood pressure. Abnormal cholesterol levels and high blood pressure in combination should be aggressively treated with lifestyle changes and medication as recommended by a physician.
- Proper diet. The ADA strongly recommends that people with diabetes restrict saturated fats to less than 7 percent of their total calories and avoid artificial trans fats. Saturated fats most often originate from animals and are known to raise blood cholesterol levels. Monounsaturated fats such as olive oil are known to improve levels of HDL. Foods high in fiber help control cholesterol as well as glucose (blood sugar), and 25 to 35 grams of fiber should be eaten each day.
- Maintaining a healthy weight. People with diabetes should maintain a weight that is appropriate for their age, sex and body proportions. Physical activity and a nutritious diet can help. Weight loss is important for those who are overweight.
- Exercise. Regular exercise raises levels of HDL cholesterol and lowers levels of LDL cholesterol and triglycerides. It also counters many of the factors that can lead to heart disease.
- Other lifestyle choices. People with diabetes should also avoid smoking (reduces HDL cholesterol levels) and limit alcohol (may increase HDL but also raises triglyceride levels and affects glucose). Limiting stress or practicing stress management may help, because stress has been linked to unhealthy changes in cholesterol levels.
- Medication. In some cases, lifestyle choices alone may not be enough to bring cholesterol levels into balance. Patients may need to combine such efforts with a regular medication therapy regimen. There are many drugs available to treat high cholesterol levels in people with diabetes, and each works differently and offers different benefits. The ADA recommends that statins be considered for people with diabetes over age 40 who have a total cholesterol level of 135 or more.
Questions for your doctor regarding cholesterol
Preparing questions in advance can help patients have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions about cholesterol and diabetes:
- What is my cholesterol level?
- What should it be?
- How often should I have my cholesterol level checked?
- How does high cholesterol complicate my diabetes?
- What is the difference among HDL, LDL, VLDL and triglycerides?
- How can my good cholesterol be increased and my bad cholesterol be decreased?
- Should I change diet, exercise or other habits to improve my cholesterol readings? Which foods should I eat more of, and which should I avoid?
- Can lowering my high blood pressure make it easier to control my cholesterol?
- Do I need to take any cholesterol drugs?
- If so, what risks and benefits do these drugs have for me?