Complications
Patients with diabetes have higher mortality rates than people who do not have diabetes regardless of sex, age, or other factors. Heart disease and stroke are the leading causes of death in these patients. All lifestyle and medical efforts should be made to reduce the risk for these conditions.
People with type 2 diabetes are also at risk for nerve damage (neuropathy) and abnormalities in both small and large blood vessels (vascular injuries) that occur as part of the diabetic disease process. Such abnormalities produce complications over time in many organs and structures in the body. Although these complications tend to be more serious in type 1 diabetes, they still are of concern in type 2 diabetes. All people with diabetes should aim for fasting blood glucose levels of less than 110 mg/dL and hemoglobin HbA1C of less than 7%.
There are two important approaches to preventing complications from diabetes:
- Intensive control of blood glucose and keeping glycosylated hemoglobin (HbA1c) levels below 7%. Tight blood glucose and HbA1c control can prevent complications due to vascular (blood vessel) abnormalities and nerve damage (neuropathy) that can cause major damage to organs, including the eyes, kidneys, and heart.
- Managing risk factors for heart disease. Control of blood glucose also helps the heart, but its benefits occur over time. It is very important that people with diabetes control blood pressure, cholesterol levels, and other factors associated with heart disease.
Hypoglycemia
Tight blood sugar (glucose) control increases the risk of low blood sugar (hypoglycemia). Hypoglycemia, also called insulin shock, occurs if blood glucose levels fall below normal. It is generally defined as blood sugar level below 70 mg/dL, although this level may not necessarily cause symptoms in all patients. Hypoglycemia may also be caused by insufficient intake of food, or excess exercise or alcohol. Usually the condition is manageable, but occasionally, it can be severe or even life threatening, particularly if the patient fails to recognize the symptoms, especially while continuing to take insulin or other hypoglycemic drugs.
Mild hypoglycemia is common among people with type 2 diabetes, but severe episodes are rare, even among those taking insulin. Still, all patients who intensively control blood sugar (glucose) levels should be aware of warning symptoms.
Risk Factors for Severe Hypoglycemia. Specific risk factors for severe hypoglycemia include:
- Patients attempting tight control of blood glucose and HbA1c levels
- Long-term diabetes
- Patients who do not comply with treatment (including those who are underinsured, have psychiatric disorders, or who are poorly educated about diabetes)
- Infections such as gastroenteritis or respiratory illnesses
Hypoglycemia unawareness. Hypoglycemia unawareness is a condition in which people become insensitive to hypoglycemic symptoms. It affects about 25% of patients who use insulin, nearly always people with type 1 diabetes. In such cases, hypoglycemia appears suddenly, without warning, and can escalate to a severe level. Even a single recent episode of hypoglycemia may make it more difficult to detect the next episode. With vigilant monitoring and by rigorously avoiding low blood glucose levels, patients can often regain the ability to sense the symptoms. However, even very careful testing may fail to detect a problem, particularly one that occurs during sleep.
Hypoglycemia Symptoms. Mild symptoms usually occur at moderately low and easily correctable levels of blood glucose. They include:
- Sweating
- Trembling
- Hunger
- Rapid heartbeat
Severely low blood glucose levels can cause neurologic symptoms such as:
- Confusion
- Weakness
- Disorientation
- Combativeness
- In rare and worst cases, coma, seizure, and death
Diabetic Ketoacidosis (DKA)
Diabetic ketoacidosis (DKA) is a life-threatening complication caused by insulin depletion. Until recently, it was a complication almost exclusively of type 1 diabetes. In such cases, it is nearly always due to noncompliance with insulin treatments. However, DKA is being reported increasingly in type 2 diabetes, especially among Hispanic- and African-Americans. It is not clear what causes total insulin depletion in these patients. Researchers are trying to learn which individuals are at particular risk.
Diabetic ketoacidosis often develop as follows:
- The process is usually triggered in insulin-deficient patients by a stressful event, most often pneumonia or urinary tract infections. Other triggers include alcohol abuse, physical injury, pulmonary embolism, heart attacks, or other illnesses.
- Severely low insulin levels cause excessive amounts of glucose in the bloodstream (hyperglycemia).
- Fat breakdown then accelerates and increases the production of fatty acids.
- These fatty acids are converted into chemicals called ketone bodies, which are toxic at high levels.
Symptoms and complications may include:
- Nausea and vomiting
- Abnormally deep and rapid breathing with frequent sighing
- Rapid heartbeat
- If the condition persists, coma and, eventually, death, may occur; however, over the past 20 years, death from DKA has decreased to about 2% of all cases.
- Other serious complications from DKA include aspiration pneumonia and adult respiratory distress syndrome.
Life-saving treatment uses rapid rehydration with a saline solution followed by low-dose insulin and potassium replacement.
Heart Disease
Heart attacks account for 60% and strokes for 25% of deaths in patients with diabetes. Diabetes affects the heart in many ways:
- Both type 1 and 2 diabetes speed the progression of atherosclerosis (hardening of the arteries). Diabetes can adversely affect blood lipid levels by lowering HDL ("good cholesterol") and increasing triglycerides. This can lead to coronary artery disease, heart attack, or stroke. According to a 2007 study, the risk of stroke doubles within 5 years of type 2 diabetes diagnosis.
- Impaired nerve function (neuropathy) associated with diabetes also causes heart abnormalities. Some experts estimate that the mortality rates from neuropathy-related heart conditions range between 15 - 53%.
- Women with diabetes are at particularly high risk for heart problems. A 2007 study indicated that while progress has been made in reducing mortality rates among men with diabetes, women with diabetes continue to face a high risk of death from heart disease and overall causes.
Results from the Diabetes Control and Complications Trial (DCCT) prove that intensive blood sugar control reduces the long-term risk of heart disease complications by 50%. Intensive blood sugar control is even more important in reducing these risks than blood pressure- and cholesterol-lowering drugs. Researchers continued to follow these patients’ progress during the next 17 years. The benefits of tight blood glucose control persist over time and may halve the risk of heart attack, stroke, angina, or coronary artery disease.
Reducing Blood Pressure. Strict control of blood pressure is critical for preventing complications of diabetes and has proven to improve survival rates. Patients should strive for blood pressure levels of less than 130/80 mm Hg (systolic/diastolic). High systolic blood pressure during sleep often occurs before development of nephropathy. (Systolic pressure is the first and higher number in a blood pressure reading.) Home blood pressure monitoring, may help identify patients with type 1 diabetes who are at risk for kidney damage. [For more information, see In-Depth Report #14: High blood pressure.]
Improving Cholesterol and Lipid Levels. Abnormal cholesterol and lipid levels are common in diabetes. High LDL (“bad”) cholesterol should always be lowered, but people with diabetes also often have additional harmful imbalances, including low HDL (“good”) cholesterol and high triglycerides.
Adult patients should aim for LDL levels below 100 mg/dL, HDL levels over 50 mg/dL, and triglyceride levels below 150 mg/dL. Patients with diabetes and heart disease should strive for even lower LDL levels; the American Diabetes Association recommends LDL levels below 70 mg/dL for these patients.
Pediatric patients should be treated for LDL cholesterol above 160 mg/dL, or above 130 mg/dL if other cardiovascular risk factors are present.
[For more information, see In-Depth Report #23: Cholesterol.]
Kidney Damage (Nephropathy)
Kidney disease (nephropathy) is a very serious complication of diabetes. With this condition, the tiny filters in the kidney (called glomeruli) become damaged and leak protein into the urine. Over time this can lead to kidney failure. Urine tests showing microalbuminuria (small amounts of protein in the urine) are important markers for kidney damage.
Diabetic nephropathy, the leading cause of end-stage renal disease (ESRD), occurs in about 20 - 40% of patients with diabetes. If the kidneys fail, dialysis is required. Symptoms of kidney failure may include swelling in the feet and ankles, itching, fatigue, and pale skin color.
Nerve Disorders (Neuropathy)
Diabetes reduces or distorts nerve function, causing a condition called neuropathy. Neuropathy refers to a group of disorders that affect nerves. The two main types of neuropathy are:
-
Peripheral (affects nerves in the toes, feet, legs, hand, and arms)
-
Autonomic (affects nerves that help regulate digestive, bowel, bladder, heart, and sexual function)
Peripheral neuropathy particularly affects sensation. It is a common complication that affects nearly half of people with type 1 or type 2 diabetes after 25 years. The most serious consequences of neuropathy occur in the legs and feet and pose a risk for ulcers and, in very severe cases, amputation. Peripheral neuropathy usually starts in the fingers and toes and moves up to the arms and legs (called a stocking-glove distribution). Symptoms include:
- Tingling
- Weakness
- Burning sensations
- Loss of the sense of warm or cold
- Numbness (if the nerves are severely damaged, the patient may be unaware that a blister or minor wound has become infected)
- Deep pain
Autonomic neuropathy can cause:
- Digestive problems (constipation, diarrhea, nausea, vomiting)
- Bladder infections and incontinence
- Erectile dysfunction
- Heart problems. Neuropathy may mask angina, the warning chest pain for heart disease and heart attack. Patients with diabetes should be aware of other warning signs of a heart attack, including sudden fatigue, sweating, shortness of breath, nausea, and vomiting.
- Rapid heart rates
- Lightheadedness when standing up (orthostatic hypotension)
Blood sugar control is an essential component in the treatment of neuropathy. Studies show that tight control of blood glucose levels delays the onset and slows progression of neuropathy. Heart disease risk factors may increase the likelihood of developing neuropathy. Lowering triglycerides, losing weight, reducing blood pressure, and quitting smoking may help prevent the onset of neuropathy.
Foot Ulcers and Amputations
About 15% of patients with diabetes have serious foot problems. They are the leading cause of hospitalizations for these patients.
Diabetes is responsible for more than half of all lower limb amputations performed in the U.S. Each year there are about 88,000 non-injury amputations, 50 - 75% of them due to diabetes. About 85% of amputations start with foot ulcers, which develop in about 12% of people with diabetes.
Those most at risk are people with a long history of diabetes, and people with diabetes who are overweight or who smoke. People who have the disease for more than 20 years and are insulin-dependent are at the highest risk. Related conditions that put people at risk include peripheral neuropathy, peripheral artery disease, foot deformities, and a history of ulcers. [For more information, see In-Depth Report #102: Peripheral artery disease and intermittent claudication.]
In general, foot ulcers develop from infections, such as those resulting from blood vessel injury. A 2006 study reported that people with diabetes who develop foot infections are 155 times more likely to have an amputation than people who did not develop infections. Foot infections often develop from injuries. Even minor infections can develop into severe complications. Numbness from nerve damage, which is common in diabetes, compounds the danger since the patient may not be aware of injuries. About one-third of foot ulcers occur on the big toe.
Charcot Foot. Charcot foot or Charcot joint (medically referred to as neuropathic arthropathy) occurs in up to 2.5% of people with diabetes. Early changes appear similar to an infection, with the foot becoming swollen, red, and warm. Gradually, the affected foot can become deformed. The bones may crack, splinter, and erode, and the joints may shift, change shape, and become unstable. It typically develops in people who have neuropathy to the extent that they cannot feel sensation in the foot and are not aware of an existing injury. Instead of resting an injured foot or seeking medical help, the patient often continues normal activity, causing further damage.
Charcot foot is initially treated with strict immobilization of the foot and ankle; some centers use a cast that allows the patient to move and still protects the foot. When the acute phase has passed, patients usually need lifelong protection of the foot using a brace initially and custom footwear.
Retinopathy and Eye Complications
Diabetes accounts for 12,000 - 24,000 of new cases of blindness annually and is the leading cause of new cases of blindness in adults age 20 - 74. The most common eye disorder in diabetes is retinopathy. People with diabetes are also at higher risk for developing cataracts and certain types of glaucoma, such as primary-open angle glaucoma (POAG). The risk for POAG is especially high for women with type 2 diabetes. [For more information, see In-Depth Report #26: Cataracts and In-Depth Report #25: Glaucoma.]
Description of Retinopathy. Retinopathy is a condition in which the retina in the eye becomes damaged. The two primary abnormalities that occur are a weakening of the blood vessels in the retina and the obstruction in the capillaries -- probably from very tiny blood clots. Retinopathy generally occurs in one or two phases:
- The early and more common type of this disorder is called nonproliferative or background retinopathy. The blood vessels in the retina are abnormally weakened. They rupture and leak, and waxy areas may form. If these processes affect the central portion of the retina, swelling may occur, causing reduced or blurred vision.
- If the capillaries become blocked and blood flow is cut off. Soft, "woolly" areas may develop in the retina's nerve layer. These woolly areas may signal the development of proliferative retinopathy. Often there are no symptoms of progressing retinopathy. In this more severe condition, new abnormal blood vessels form and grow on the surface of the retina. They may spread into the cavity of the eye or bleed into the back of the eye. Major hemorrhage or retinal detachment can result, causing severe visual loss or blindness. The sensation of seeing flashing lights may indicate retinal detachment.
Mental Function and Dementia
Some studies indicate that patients with type 2 diabetes face a higher than average risk of developing dementia caused either by Alzheimer's disease or problems in blood vessels in the brain. Problems in attention and memory can occur even in people under age 55 who have had diabetes for a number of years.
Infections
Respiratory Infections. People with diabetes face a higher risk for influenza and its complications, including pneumonia, possibly because the disorder neutralizes the effects of protective proteins on the surface of the lungs. In fact, deaths among people with diabetes increase by 5 - 15% during flu epidemics, and they are six times more likely to be hospitalized with complications from flu than nondiabetic patients who have flu. Everyone with diabetes should have annual influenza vaccinations and a vaccination against pneumococcal pneumonia.
Urinary Tract Infections. Women with diabetes face a significantly higher risk for urinary tract infections, which are likely to be more complicated and difficult to treat than in the general population.
Depression
Diabetes doubles the risk for depression. According to one study, depression, in turn, increases the risk for hyperglycemia and complications of diabetes. Restoring mental health, both through medication and psychotherapy, not only improves quality of life but may help patients control their blood sugar levels.
Changes in Bone Quality
Diabetes changes bone quality and density, but the effects differ, depending on type:
- Type 1 diabetes is associated with a slightly reduced bone density, putting patients at risk for osteoporosis and possibly fractures. The best medications for bone loss in patients with diabetes are bisphosphonates, such as alendronate (Fosamax) and risedronate (Actonel). They not only help prevent bone loss but may even reduce daily insulin requirements in patients taking insulin. [For more information, see In-Depth Report #18: Osteoporosis.]
- Type 2 diabetes, on the other hand, is associated with an increased bone density but is also associated with fractures. In such cases, the bone quality itself may be impaired.
Older patients with either type of diabetes are at risk for falling, which compounds the risk for fracture.
Other Complications
Diabetes increases the risk for other conditions, including:
- Hearing loss
- Periodontal disease
- Carpal tunnel syndrome
- Nonalcoholic fatty liver disease, also called nonalcoholic steatohepatitis (NASH), a particular danger for people who are obese
- Colorectal cancer
- Uterine cancer
