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):

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.