Family doctor

Overview

• People with diabetes are at high risk of developing coronary heart disease (CHD).
• Type 2 diabetics cholesterol results tend to show low high density lipoproteins (HDL), variable low density lipoproteins (LDL) and high triglyceride levels, making them prone to development of narrowed arteries and developing CHD.
• Diabetic's cholesterol results need to be examined differently than those of the general population, and will be interpreted in the light of other risk factors.
• Lifestyle changes to control cholesterol levels are those generally recommended to diabetics for control of blood glucose. Studies show reducing blood pressure and careful control of blood glucose levels are very important for reducing the risk of CHD.
• Traditional cholesterol reducing treatment may involve the use of statin or fibrate drugs, in some cases in combination.
• Ongoing and future studies show promise of developing specific treatments for diabetics at risk of developing CHD and with abnormal cholesterol levels.

Are diabetics more at risk of developing CHD?

Generally the results of studies show, even with treatment, diabetics are more at risk of coronary heart disease (CHD) than non diabetics. Type 2 diabetics are much more at risk of developing CHD than the general population.

What factors put diabetics more at risk?

In particular, the following factors put type 2 diabetics at far greater risk of developing CHD:

• smoking
• high blood pressure
• poor blood glucose control
• abnormal HDL and HDL cholesterol levels

 Additionally, the following type 2 diabetics are more at risk:

• males or post menopausal woman
• particular cultures and ethnic groups
• those with insulin resistance
• older patients and those having type 2 diabetes for extended period

Do cholesterol levels matter?

Studies consistently show diabetics to have abnormal cholesterol levels, and as cholesterol affects the development of CHD in the general population, it is considered important. However studies of diabetics also show careful management of blood pressure and blood glucose levels are very important for controlling CHD.

Type 1 diabetics with good blood glucose control show relatively normal cholesterol levels, however type 2 diabetics or patients with poor glucose tolerance tend to have cholesterol levels that put them at risk of coronary heart disease (CHD).

Type 2 diabetics tend to have low levels of high density lipoproteins (HDL), variable low density lipoproteins (LDL) and high triglyceride levels.

Why are the various cholesterol levels important?

In general terms, too much LDL cholesterol causes damage (atherosclerosis) to artery walls. The build up of LDL results in narrowing of the arteries and as a result is often referred to as "bad" cholesterol.

Some of the adverse affects of LDL cholesterol are reduced by (HDL) cholesterol, which is thought to remove LDL cholesterol from the artery walls, hence often referred to as "good" cholesterol.

High triglyceride levels are believed to lead to abnormal breakdown of lipoproteins in the blood, which in turn adversely affects the levels of HDL and LDL.

Lack of blood supply due to narrowed arteries can affect the heart (causing angina), the legs (causing claudication) and brain (causing transient ischaemic attacks, "TIAs"). If the artery blocks off completely it can cause a heart attack or stroke.

As type 2 diabetics tend to have low "good" cholesterol levels; variable "bad" cholesterol levels; and high triglycerides which affect the good and bad cholesterol for the worse, they are prone to development of narrowed arteries resulting in CHD.

How do diabetics know if their cholesterol levels are abnormal?

A doctor can arrange for blood tests to be analysed to show cholesterol levels. Tests for triglyceride levels may be taken after a fasting period. A combination of cholesterol tests will give a doctor a good picture of a patient's overall cholesterol levels.

The cholesterol results alone may not appear to put a diabetic at risk of CHD, when compared with cholesterol levels of the general population. However diabetics have many other factors that, when combined, put them at greater risk. Because of this, the cholesterol results will be interpreted in the light of these other risk factors.

What are the treatment options?

A checklist used by doctors to reduce CHD in diabetics patients includes:

• reducing blood pressure to less than 130/85
• careful control of blood glucose (HbA1c less than 7%)
• reducing LDL to equal or below 3.0mmol/L
• correcting low HDL levels
• use of aspirin
• use of ACE inhibitors
• use of beta-blockers.

Studies of coronary heart disease(CHD ) including diabetic patients show careful control of blood glucose levels, reduction of blood pressure and correction of abnormal cholesterol levels certainly reduce the risk of developing heart disease.

For those diabetics who have suffered a CHD episode(eg heart attack or angina), beta-blockers, aspirin and ACE inhibitors have been shown to prolong life expectancy and reduce further CHD events.

Some doctors may also recommend the use of cholesterol reducing treatments.

What treatment methods are commonly used for diabetics with abnormal cholesterol levels?

There are numerous treatment options for those with abnormal cholesterol levels, however none to date have been developed specifically for diabetics. However many diabetics have been included in these studies, so some results are available. There are studies currently underway concentrating solely on diabetics.

The traditional intervention treatments used for diabetics with abnormal cholesterol levels are:

• statins
• fibrates

Statins tend to lower elevated LDL cholesterol levels, whereas fibrates act more on triglyceride levels as well. In some cases these treatments may be combined. When used in combination it is important for diabetics to carefully monitor any muscle aches and effects on liver functioning(blood tests).

A careful choice of cholesterol treatment is required, taking into account the individual's cholesterol levels and any other health factors.

What can diabetics do to lessen the chances of developing coronary heart disease ( CHD)?

Recommended lifestyle changes to lower the risk of CHD include:

• low fat diet
• stop smoking
• increased exercise
• reduction of body fat if necessary
• moderate or no alcohol intake.

These changes help to lower blood pressure, reduce dietary cholesterol intake and levels and reduce weight.

For those diabetics already taking these factors into account to managing their diabetes, this list does not provide new opportunities to reduce CHD risk. This group should concentrate on consistent blood glucose control and reduction of blood pressure, and discuss cholesterol control with their doctor.

What do ongoing and new diabetes and cholesterol studies show?

There are a number of ongoing studies that may prove promising for diabetics controlling cholesterol and reducing the risk of CHD.

A current study into the use of a particular ACE inhibitor (the HOPE study using ramipril) shows encouraging results for reducing CHD and stroke risk in diabetics.

To date, treatment using niacin to reduce cholesterol has generally been avoided for diabetics as it may worse glucose intolerance. However, two very recent studies indicate therapeutic doses of niacin can safely be used by diabetics for the control of cholesterol disorders without adversely affecting their blood sugar levels.

A study in 1999 showed the insulin sensitiser pioglitazone, taken orally either alone or in combination with other oral therapies, lowered cholesterol and triglyceride levels.

Recently the US Food and Drug Administration has approved the production of HDL-cholesterol test strips for use by consumers, as part of a small hand held blood chemistry system designed for the management of diabetes and its complications. Test strips currently available for the system are glucose, ketone, total cholesterol and HDL-cholesterol. Triglyceride test strips are pending FDA clearance and the company has direct LDL, microalbumin and haemoglobin A1c in development.