Diabetes and cardiovascular disease often go hand-in-hand. Adults with diabetes are two to four times more likely to develop heart disease or have a stroke than people without diabetes. In fact, about 68 percent of people with diabetes die of heart disease or stroke-one more factor that makes cardiovascular disease the most common cause of death in both men and women.
In addition, people with diabetes often have a build-up of atherosclerotic plaque throughout the body. About one in three people with diabetes over the age of 50 has peripheral arterial disease (PAD), which is the narrowing of blood vessels by plaque in parts of the body other than the heart, for example in the legs or the kidneys.
What is diabetes?
Diabetes prevents the body from properly metabolizing sugar from food and using it as fuel in the body's cells. When you digest food, most of it is broken down into glucose, a type of sugar. The glucose is then transported in the blood to individual cells to burn for energy. Insulin, a hormone made by the pancreas, is needed to get the glucose into the cells-like a key that opens a door. In healthy people, the body automatically senses how much glucose is in the bloodstream and releases the right amount of insulin. In diabetes, the pancreas doesn't make enough insulin or the cells are resistant to the insulin, or both. As a result, the amount of glucose in the blood climbs too high while the cells starve for energy.
Diabetes is a huge health problem in the United States. Some 23.6 million Americans have diabetes and, each year, 1.6 million adults are newly diagnosed with this condition. About 5 to 10 percent of people with diabetes have Type 1. Sometimes called insulin-dependent or juvenile-onset diabetes, this form of the disease typically strikes in childhood or young adulthood. It is caused by a failure of the pancreas to produce insulin, perhaps because of autoimmune disease, genetic abnormality, or injury. People with Type 1 diabetes must take insulin shots.
Type 2 diabetes is far more common, and affects 90 to 95 percent of people with diabetes. It is often linked to obesity and a lack of physical activity. In the past, this form of the disease was called adult-onset diabetes, but today more and more children are being diagnosed with Type 2 diabetes.
There are several warning signs of diabetes. They are particularly common in Type 1 diabetes. Many people with Type 2 diabetes have few or no symptoms, so damage to the blood vessels can go undetected for years. The typical symptoms of diabetes include:
- Increased thirst
- Frequent urination
- Increased hunger
- Blurred vision
- Dry mouth
- Unexplained weight loss
- Numbness of the hands or feet
- Erectile dysfunction
The relationship between diabetes and cardiovascular disease is clear, but the causes are complex. Over time, too much glucose in the blood damages nerves and blood vessels. This, in turn, can cause heart disease and stroke. In addition, damage to the blood vessels in the legs can result in poor circulation and increase the risk of foot ulcers and amputations, while damage to the blood vessels that supply blood to the kidney can cause kidney failure and damage to the small blood vessels in the eye can eventually cause blindness.
High blood glucose levels don't fully explain the relationship between diabetes and cardiovascular disease. People with diabetes also tend to have low-level inflammation of the lining of the arteries, which can interfere with the proper function of the blood vessels and make them more susceptible to developing atherosclerotic plaque. In addition, with diabetes there is a greater tendency for blood cells to clump together to form blood clots within the blood vessels. A blood clot that blocks the arteries supplying blood to the heart causes a heart attack, while a blood clot that blocks an artery supplying blood to the brain causes a stroke.
The blood vessels in patients with diabetes are also more vulnerable to the harmful effects of other heart disease risk factors. These risk factors include:
- High blood pressure
- Abnormal blood lipids--High LDL (bad) cholesterol
- High triglycerides
- Low HDL (good) cholesterol
- Lack of physical activity
- Poorly controlled blood glucose levels
- Insulin resistance (common in Type 2 diabetes)
More than 90 percent of people with diabetes have at least one of these additional heart disease risk factors.
Symptoms of heart attack, stroke, and PAD
Diabetes increases the risk of having a heart attack, but it may also change the symptoms and make diagnosis more difficult. Classic symptoms of a heart attack are:
- Pain or a tightness in the chest
- Pain or discomfort in the arms, back, jaw, neck, or stomach
- Shortness of breath
- Anxiety, or a sense of doom
Because of nerve damage, people with diabetes may not have typical chest pain during a heart attack. Instead, they may experience milder chest pressure or sudden shortness of breath or sweating, or even an unexplainable change in blood glucose levels.
When people with diabetes have a stroke, the results may be more devastating than for other patients. That's because with diabetes, the arteries throughout the body-including the brain-are often narrowed by atherosclerosis. As a result, when an artery in the brain becomes blocked by a blood clot, causing a stroke, there are fewer alternate routes for blood to flow to the affected part of the brain.
The symptoms of a stroke include:
- Sudden numbness or weakness in the face, arm, or leg (especially on one side of the body)
- Difficulty speaking or understanding words; confusion
- Sudden blurred vision or decreased vision in one or both eyes
- Sudden difficulty swallowing
- Dizziness or loss of balance
- Brief loss of consciousness
- Sudden inability to move part of the body (paralysis)
- Sudden severe headache
Both heart attack and stroke are emergencies that require immediate treatment. If you experience any of these symptoms, call 911.
Blockages in the arteries that supply blood to the legs and feet are very common in people with diabetes, particularly after the age of 50. Smoking increases the risk of PAD even more. The symptoms of PAD include:
- Pain or cramping in the legs while walking or climbing stairs that gets better with rest
- Slowly healing wounds on the legs or feet
- A lower temperature in one leg as compared to the other
- Weak pulses in one or both legs
- Abnormal skin, hair or nails on the legs or feet
Diagnosing cardiovascular disease
If you have diabetes, your primary care physician may already have talked with you about the importance of taking care of your heart and blood vessels. If not, you should bring up the topic and ask your doctor to evaluate how high your risk for cardiovascular disease is and what you should do to prevent a heart attack, stroke or PAD.
To assess your risk for cardiovascular disease, your doctor will ask you questions about your family history, diet, exercise, stress level and whether you smoke. Your doctor will also check your blood pressure and body weight, and order or review key blood tests, including:
- Cholesterol, including total, HDL and LDL cholesterol
- Triglycerides, a kind of fat often elevated in people with diabetes
- Hemoglobin A1C, which measures average blood glucose levels over time
- High-sensitivity C-reactive protein (CRP), which measures inflammation in your body and blood vessels
Your doctor may also want you to have certain diagnostic tests, including the following:
- Electrocardiogram (ECG), which records the electrical activity in your heart and can detect abnormalities that suggest the heart may not be getting enough blood flow in certain areas
- Coronary artery calcium scoring, which is performed as part of a CT scan and helps your doctor determine your risk for developing serious heart disease by measuring the amount of calcified atherosclerotic plaque in your arteries
If your initial test results indicate increased risk, or if you are having worrisome symptoms such as chest pain or unexpected shortness of breath during physical activity, your doctor may refer you for further testing, including:
- Stress testing, which evaluates how much blood flow is getting to the heart and how effectively the heart is pumping during exercise or another type of physical stress
- Echocardiography, which uses ultrasound to evaluate how well the heart is pumping and whether the heart muscle has become abnormally thick as a result of high blood pressure
- Coronary angiography, which involves threading a slender, flexible tube into the arteries of your heart and injecting x-ray dye to enable an interventional cardiologist to see inside your arteries, find any plaques and measure how severe they are
If your doctor suspects that cholesterol plaque is clogging the arteries in your legs or body organs, additional diagnostic tests may be needed. These may include:
- Ultrasound, which uses sound waves to evaluate blood flow through the arteries
- Noninvasive angiography, using computed tomography (CT) or magnetic resonance imaging (MRI) to create detailed images of the arteries without placing any instruments or tubes into the body
- Conventional angiography, which is similar to coronary angiography but involves arteries that supply blood to organs other than the heart
The ankle-brachial index (ABI) is also very helpful in diagnosing PAD in the legs and determining how severe it is. During an ABI test, your doctor will use a blood pressure cuff and a special ultrasound probe to compare blood pressure readings in the arm and lower leg on the same side of the body. If the blood pressure in the ankle is substantially lower than in the arm, it is a sign that a blockage is interfering with blood flow to the lower leg. The ABI provides important information for predicting the likelihood of serious problems such as foot wounds that won't heal or the need for surgery to restore blood flow to a limb.
Many people with diabetes develop at least mild cardiovascular disease. Therefore, treatment consists of a strong program for preventing further damage to the heart and blood vessels, coupled with specific therapies for problems that already exist. Whether plaque build-up affects the arteries of the heart, legs, brain or other organs, effective prevention and treatment are likely to involve lifestyle changes, such as diet, exercise, stress management and quitting smoking; medications to control blood sugar, blood pressure and cholesterol levels; and possibly daily aspirin to ward off unwanted blood clots.
In the case of severe plaque build-up, treatment may involve catheter-based interventions such as stenting to widen the diseased artery and hold it open. In some cases, surgery may be needed to bypass the blockage and re-route blood flow through a new vessel or-in the case of the arteries that supply blood to the brain-to scrape and remove the plaque from the artery wall, restoring adequate blood flow.
Prevention and treatment
The best way to prevent cardiovascular disease is to take good care of yourself and keep your diabetes under control. Start with the ABCs of diabetes management:
A is for A1C. The A1C test gives your doctor important insight into your blood glucose levels over the previous two to three months. It's a good idea to check your A1C level twice a year. For most people, the goal is an A1C of less than 7 percent.
B is for blood pressure. When a person with diabetes also has high blood pressure, the risk for cardiovascular disease doubles. High blood pressure forces the heart to work harder to circulate blood, and can lead to a heart attack, stroke, and kidney damage. Studies have also shown that there is a link between high blood pressure and resistance to insulin by the body's cells. For people with diabetes, the goal is a blood pressure of less than 130/80 mmHg.
C is for cholesterol. In people with diabetes, LDL, or "bad" cholesterol, tends to build up and clog the arteries. Triglycerides, another form of fat that can cause atherosclerosis, also tend to be abnormally high in diabetes. HDL, or "good" cholesterol helps keep the arteries healthy by removing cholesterol from the body. In diabetes, HDL levels tend to be lower than normal. This combination of abnormal lipid levels is often seen in people with premature heart disease.
For most people, target blood levels of these lipids are:
- Total cholesterol, less than 200 mg/dL
- LDL cholesterol, less than 100 mg/dL (lower for people who already have heart disease)
- Triglycerides, less than 150 mg/dL
- HDL cholesterol, greater than 40 mg/dL for men and greater than 50 mg/dL for women
In addition to the ABCs of diabetes care, there are many steps you can take to stay healthy.
Diet: The great thing about a heart-healthy diet is that it's good for everyone, including people with diabetes. In general, your diet should be nutritionally balanced, high in fiber, low in fat (especially saturated fat) and moderate-to-low in salt. Load up with vegetables; choose lean meats, chicken and fish-and prepare them by baking or broiling; choose low-fat or fat-free dairy products; avoid high-sodium processed foods and limit how much salt you add to food; and enjoy some fresh fruit every day. As for how much you should eat of starchy foods like bread, pasta, potatoes and rice, follow the advice of your doctor and dietitian. Finally, watch the calories. Too much of any food can cause you to gain weight, and that will make it hard to control your diabetes.
Alcohol. If you choose to drink alcohol, limit it to one drink for women and two drinks for men per day. (One drink is a 12-ounce beer, a 4-ounce glass of wine, or 1.5 ounces of distilled alcohol.) Keep in mind that alcohol has a lot of calories. In addition, it tends to raise blood levels of triglycerides.
Exercise. Increasing your physical activity is one of the best ways to reduce the risk for heart attack and stroke. Exercise can help you to lose weight, prevent or delay the onset of Type 2 diabetes, reduce blood pressure, and relieve stress. It also helps make the body's cells more responsive to insulin. The goal for most people is at least 30 to 60 minutes of exercise on most days of the week.
Smoking. Cigarette smoke is not only bad for the lungs, it's toxic to the blood vessels and increases the risk of heart attack and stroke. People with diabetes are especially vulnerable to the bad effects of smoking. Quitting smoking is difficult, but it is well worth the effort. Talk with your doctor about getting help with smoking cessation.
Body weight. Obesity is not only a major risk factor for cardiovascular disease, it plays a central role in insulin resistance and has been linked to high blood pressure. If you are overweight, losing those extra pounds will reduce your risk of heart attack and stroke, improve your sensitivity to insulin and help you to control your blood sugar levels.
Medications. People with diabetes know how important it is to take insulin or oral anti-diabetic medications. It's just as essential to take medications to prevent or treat cardiovascular disease, if your doctor has prescribed them. Depending on your individual health needs, you may need to take the following:
- Blood pressure medication. Anyone who has both diabetes and high blood pressure should be treated with medication to bring the blood pressure down to 130/80 mmHg or less. Many doctors will prescribe a type of medication known as an ACE inhibitor (or a related medication known as an ARB). These medications not only control the blood pressure, they appear to protect the heart and kidneys, so they are especially helpful in people with diabetes. If you need more than one medication to keep your blood pressure under control, your doctor may also prescribe a thiazide diuretic, a beta blocker, or a calcium-channel blocker.
- Cholesterol-lowering medication. If your LDL cholesterol is high, your doctor may prescribe a statin. If your triglycerides are high, it may be necessary to take niacin or a fibrate medication.
- Aspirin. Low-dose aspirin (75 to 162 mg daily) is recommended for people who know they have coronary artery disease (e.g., someone who has had a heart attack in the past). But for those who want to prevent cardiovascular disease from developing, aspirin's role is less clear. The American Diabetes Association, American Heart Association and American College of Cardiology recently released joint recommendations that address this question. The recommendations reflect a balance between aspirin's moderate benefit in reducing the risk for cardiovascular disease and its potential to increase the risk of bleeding from the stomach and gastrointestinal tract. Current recommendations for the prevention of vascular disease state:
- Low-dose aspirin is reasonable for adults with diabetes who are not at increased risk for gastrointestinal bleeding but are at increased risk for cardiovascular disease (i.e., older than age 50 for men and age 60 for women PLUS at least one major heart disease risk factor).
- Low-dose aspirin might be considered for adults with diabetes who are at intermediate risk for cardiovascular disease (i.e., younger patients with one or more risk factors, or older patients with no risk factors).
- Aspirin is not be recommended for adults with diabetes at low risk for cardiovascular disease (men under age 50 and women under age 60 with no major risk factors).
Revascularization. If you develop cardiovascular disease, you may eventually need a revascularization procedure. The term revascularization simply means to restore blood flow to the heart or another organ after the arteries have become clogged with cholesterol plaque. In the case of the heart, this can be accomplished either with coronary artery bypass graft (CABG) surgery or angioplasty and stenting. Angioplasty and stenting are minimally invasive catheter procedures that together are known as PCI (percutaneous coronary intervention).
Whether people with diabetes fare better with CABG surgery or PCI is an ongoing controversy. That's because there haven't been many clinical studies that specifically focused on how to treat narrowed coronary arteries in people with diabetes. In addition, cardiovascular disease is different-and more severe-in people with diabetes. For example, people with diabetes often have widespread atherosclerosis affecting many arteries, not just a single blockage. Plaque deposits are often longer and affect smaller blood vessels in patients with diabetes. And after a PCI procedure, it is more common in people with diabetes to find that the artery has become obstructed again, this time by an overgrowth of scar tissue. Known as restenosis, this complication explains why patients with diabetes are more likely to need repeat procedures after PCI when compared to non-diabetic patients.
For many years it was believed that CABG was the best choice for people with diabetes, mostly because early studies showed that long-term survival was better with surgery than with PCI. But more recent studies (see SCAI Statement on the BARI 2D Trial and SCAI Statement on the SYNTAX Trial) have started to change the way people think. Now that drug-eluting stents are available, many interventional cardiologists believe that PCI is a good option for certain people with diabetes, depending on how widespread the coronary artery disease is and how complex each cholesterol plaque is. Another large study (see Drug-Eluting or Bare-Metal Stenting in Patients With Diabetes Mellitus) is under way and will provide more answers.
If you have PAD, treatment will include medication and lifestyle changes, just as with coronary artery disease. Getting more exercise and quitting smoking are especially important. Depending on how severe your PAD is and how you respond to initial therapy, you may also need revascularization to make sure your legs and feet are getting enough blood flow. Whether the best treatment is surgery or a minimally invasive catheter procedure will depend on the specific type of blockage and which artery is involved.
You may also need revascularization because of plaque build-up in a carotid artery, which supplies blood to the brain. For now, most patients are treated with a surgical procedure known as carotid endarterectomy (CEA). This procedure involves opening the artery, cutting or scraping away the plaque and removing it.
However, for years, researchers have been conducting clinical studies to determine which types of patients and which types of plaques could be safely and effectively treated with a minimally invasive catheter procedure known as carotid artery stenting (CAS). Growing evidence supports the use of CAS in an increasingly wide range of patients with carotid artery disease, though not in all patients. Recommendations and guidelines are being revised on a ongoing basis as new evidence becomes available.
The bottom line is, whether you have heart disease, PAD, or carotid artery disease, the choice between surgery and catheter-based interventions like angioplasty and stenting must take into account your medical history and individual preferences, and should be made after a careful discussion with your physician.