(See also Diabetes Mellitus Diabetes Mellitus (DM) Diabetes mellitus is a disorder in which the body does not produce enough or respond normally to insulin, causing blood sugar (glucose) levels to be abnormally high. Urination and thirst are... read more .)
There are two types of diabetes mellitus:
Type 1 Type 1 diabetes Diabetes mellitus is a disorder in which the body does not produce enough or respond normally to insulin, causing blood sugar (glucose) levels to be abnormally high. Urination and thirst are... read more , in which the body's immune system attacks the insulin-producing cells of the pancreas, and more than 90% of them are permanently destroyed
Type 2 Type 2 diabetes Diabetes mellitus is a disorder in which the body does not produce enough or respond normally to insulin, causing blood sugar (glucose) levels to be abnormally high. Urination and thirst are... read more , in which the body develops resistance to the effects of insulin
In both types, the amount of sugar (glucose) in the blood is elevated.
People with either type 1 or type 2 diabetes are likely to have complications as a result of the elevated glucose level. However, because type 2 diabetes may be present for some time before it is diagnosed, complications in type 2 diabetes may be more serious or more advanced when they are discovered.
People with diabetes mellitus may experience many serious, long-term complications. Some of these complications begin within months of the onset of diabetes, although most tend to develop after a few years. Most of the complications gradually worsen. In people with diabetes, strictly controlling the level of glucose in the blood makes these complications less likely to develop or worsen.
Causes of Complications of Diabetes Mellitus
Most complications of diabetes are the result of problems with blood vessels. Glucose levels that remain high over a long time cause both the small and large blood vessels to narrow. The narrowing reduces blood flow to many parts of the body, leading to problems. There are several causes of blood vessel narrowing:
Complex sugar-based substances build up in the walls of small blood vessels, causing them to thicken and leak.
Poor control of blood glucose levels causes the levels of fatty substances in the blood to rise, resulting in atherosclerosis Atherosclerosis Atherosclerosis is a condition in which patchy deposits of fatty material (atheromas or atherosclerotic plaques) develop in the walls of medium-sized and large arteries, leading to reduced or... read more and decreased blood flow in the larger blood vessels.
Types of Diabetes Complications
Blood vessel complications in diabetes
Atherosclerosis leads to heart attacks Acute Coronary Syndromes (Heart Attack; Myocardial Infarction; Unstable Angina) Acute coronary syndromes result from a sudden blockage in a coronary artery. This blockage causes unstable angina or a heart attack (myocardial infarction), depending on the location and amount... read more and strokes Overview of Stroke A stroke occurs when an artery to the brain becomes blocked or ruptures, resulting in death of an area of brain tissue due to loss of its blood supply (cerebral infarction). Symptoms occur suddenly... read more . Atherosclerosis is between 2 and 4 times more common and tends to occur at a younger age in people with diabetes than in people who do not have diabetes.
Over time, narrowing of blood vessels can harm the heart, brain, legs, eyes, kidneys, nerves, and skin, resulting in angina Angina Angina is temporary chest pain or a sensation of pressure that occurs while the heart muscle is not receiving enough oxygen. A person with angina usually has discomfort or pressure beneath the... read more , heart failure Heart Failure (HF) Heart failure is a disorder in which the heart is unable to keep up with the demands of the body, leading to reduced blood flow, back-up (congestion) of blood in the veins and lungs, and/or... read more , strokes Overview of Stroke A stroke occurs when an artery to the brain becomes blocked or ruptures, resulting in death of an area of brain tissue due to loss of its blood supply (cerebral infarction). Symptoms occur suddenly... read more , leg cramps during walking (claudication), poor vision, chronic kidney disease Chronic Kidney Disease Chronic kidney disease is a slowly progressive (months to years) decline in the kidneys’ ability to filter metabolic waste products from the blood. Major causes are diabetes and high blood pressure... read more , damage to nerves (neuropathy Polyneuropathy Polyneuropathy is the simultaneous malfunction of many peripheral nerves throughout the body. Infections, toxins, drugs, cancers, nutritional deficiencies, diabetes, autoimmune disorders, and... read more ), and skin breakdown.
Infectious problems in diabetes
People with diabetes often develop bacterial and fungal infections typically of the skin and mouth. When the levels of glucose in the blood are high, white blood cells cannot effectively fight infections. Any infection that develops tends to be more severe and takes longer to resolve in people with diabetes. Sometimes, an infection is the first sign of diabetes.
One such infection is a yeast infection called candidiasis Candidiasis Candidiasis is a fungal infection caused by several species of the yeast Candida, especially Candida albicans. The most common type of candidiasis is a superficial infection of... read more . Candida yeast is a normal resident of the mouth, digestive tract, and vagina that usually causes no harm. In people with diabetes, however, Candida can overgrow on mucous membranes and moist areas of the skin causing rashes in those areas.
People with diabetes are also particularly likely to have ulcers and infections of the feet and legs because of poor circulation to the skin. Too often, these wounds heal slowly or not at all. When wounds do not heal, they typically become infected and this can result in gangrene Gas Gangrene Gas gangrene is a life-threatening infection of muscle tissue caused mainly by the anaerobic bacteria Clostridium perfringens and several other species of clostridia. Gas gangrene can... read more (tissue death) and bone infection (osteomyelitis Osteomyelitis Osteomyelitis is a bone infection usually caused by bacteria, mycobacteria, or fungi. Bacteria, mycobacteria, or fungi can infect bones by spreading through the bloodstream or, more often, by... read more ). Amputation of the foot or part of the leg may be needed.
Eye problems in diabetes
Damage to the blood vessels of the eye can cause loss of vision (diabetic retinopathy Diabetic Retinopathy Diabetic retinopathy is damage to the retina (the transparent, light-sensitive structure at the back of the eye) as a result of diabetes. Blood vessels in the retina can leak blood and fluid... read more ). Laser surgery can seal the leaking blood vessels of the eye and prevent permanent damage to the retina. Sometimes, other forms of surgery or injectable medications may be used. Therefore, people with diabetes should have yearly eye examinations to check for early signs of damage.
Liver damage in diabetes
It is common for people with diabetes to also have fatty liver disease Fatty Liver Fatty liver is an abnormal accumulation of certain fats (triglycerides) inside liver cells. People with fatty liver may feel tired or have mild abdominal discomfort but otherwise have no symptoms... read more , in which abnormal fat deposits collect in the liver. Fatty liver disease can sometimes progress to more serious liver disease including cirrhosis Cirrhosis of the Liver Cirrhosis is the widespread distortion of the liver's internal structure that occurs when a large amount of normal liver tissue is permanently replaced with nonfunctioning scar tissue. The scar... read more . Doctors diagnose liver problems if liver blood tests are abnormal and confirm the diagnosis with a liver biopsy Biopsy of the Liver Doctors can obtain a sample of liver tissue during exploratory surgery, but more often they obtain a sample by inserting a hollow needle through the person's skin and into the liver. This type... read more . Losing weight, maintaining good control of blood sugar levels, and treating high cholesterol Dyslipidemia Dyslipidemia is a high level of cholesterol and/or triglycerides or a low level of high-density lipoprotein (HDL) cholesterol. Lifestyle, genetics, disorders (such as low thyroid hormone levels... read more can be helpful.
Kidney damage in diabetes
The kidneys can malfunction, resulting in chronic kidney disease Chronic Kidney Disease Chronic kidney disease is a slowly progressive (months to years) decline in the kidneys’ ability to filter metabolic waste products from the blood. Major causes are diabetes and high blood pressure... read more that may require dialysis Dialysis Dialysis is an artificial process for removing waste products and excess fluids from the body, a process that is needed when the kidneys are not functioning properly. There are a number of reasons... read more or kidney transplantation Kidney Transplantation Kidney transplantation is the removal of a healthy kidney from a living or recently deceased person and then its transfer into a person with end-stage kidney failure. (See also Overview of Transplantation... read more . Doctors usually check the urine of people with diabetes for abnormally high levels of protein (albumin), which is an early sign of kidney damage. At the earliest sign of kidney complications, people are often given medications that slow the progression of kidney damage, for example, sodium-glucose co-transporter-2 (SGLT2) inhibitors (medications that increase glucose secretion in the urine), angiotensin-converting enzyme (ACE) inhibitors, or angiotensin II receptor blockers (ARBs).
Nerve damage in diabetes
Damage to nerves can manifest in several ways. If a single nerve malfunctions, an arm or leg may suddenly become weak. If the nerves to the hands, legs, and feet become damaged (diabetic polyneuropathy Polyneuropathy Polyneuropathy is the simultaneous malfunction of many peripheral nerves throughout the body. Infections, toxins, drugs, cancers, nutritional deficiencies, diabetes, autoimmune disorders, and... read more ), sensation may become abnormal, and tingling or burning pain and weakness in the arms and legs may develop. Damage to the nerves of the skin makes repeated injuries more likely because people cannot sense changes in pressure or temperature.
Foot problems in diabetes
Diabetes causes many changes in the body. The following changes in the feet are common and difficult to treat:
Damage to the nerves (neuropathy) affects sensation to the feet, so that pain is not felt. Irritation and other forms of injury may go unnoticed. An injury may wear through the skin before any pain is felt.
Changes in sensation alter the way people with diabetes carry weight on their feet, concentrating weight in certain areas so that calluses form. Calluses (and dry skin) increase the risk of skin breakdown.
Diabetes can cause poor circulation in the feet, making ulcers more likely to form when the skin is damaged and making the ulcers slower to heal.
Because diabetes can affect the body’s ability to fight infections, a foot ulcer, once it forms, easily becomes infected. Because of neuropathy, people may not feel discomfort due to the infection until it becomes serious and difficult to treat, leading to gangrene Gas Gangrene Gas gangrene is a life-threatening infection of muscle tissue caused mainly by the anaerobic bacteria Clostridium perfringens and several other species of clostridia. Gas gangrene can... read more . People with diabetes are more than 30 times more likely to require amputation of a foot or leg than are people without diabetes.
Foot care is critical (see Foot Care Foot care Occlusive peripheral arterial disease is blockage or narrowing of an artery in the legs (or rarely the arms), usually due to atherosclerosis and resulting in decreased blood flow. Symptoms depend... read more ). The feet should be protected from injury, and the skin should be kept moist with a good moisturizer. Shoes should fit properly and not cause areas of irritation. Shoes should have appropriate cushioning to spread out the pressure caused by standing. Going barefoot is ill advised. Regular care from a podiatrist (a doctor specializing in foot care), such as having toenails cut and calluses removed, may also be helpful. Also, sensation and blood flow to the feet should be regularly evaluated by doctors.
Monitoring and Preventing Diabetes Complications
At the time of diagnosis and then at least yearly, people with type 2 diabetes are monitored for the presence of diabetes complications, such as kidney, eye, and nerve damage. In people with type 1 diabetes, doctors begin monitoring for complications 5 years after diagnosis. Typical screening tests include the following:
Foot examination to test sensation and look for signs of poor circulation (ulcers, hair loss)
Eye examination (done by an eye specialist)
Urine and blood tests of kidney function
Blood tests for cholesterol levels
Sometimes an electrocardiogram
Worsening of complications can be prevented or delayed by strict blood glucose control or by early treatment with medication. Risk factors for heart problems, such as increased blood pressure High Blood Pressure High blood pressure (hypertension) is persistently high pressure in the arteries. Often no cause for high blood pressure can be identified, but sometimes it occurs as a result of an underlying... read more and high cholesterol levels Overview of Cholesterol and Lipid Disorders The body needs fats (lipids) for growth and energy. It also uses them to synthesize hormones and other substances needed for the body’s activities. The body may deposit excess fat in blood vessels... read more , are evaluated at each doctor visit and are treated with medication if necessary.
Proper care of feet and regular eye examinations can help prevent or delay the onset of complications of diabetes. People with diabetes are vaccinated against Streptococcus pneumoniae, hepatitis B, and COVID-19, and doctors usually recommend they receive annual flu vaccination because people with diabetes are at risk of infection.
Treatment of high blood pressure High Blood Pressure High blood pressure (hypertension) is persistently high pressure in the arteries. Often no cause for high blood pressure can be identified, but sometimes it occurs as a result of an underlying... read more and high cholesterol Dyslipidemia Dyslipidemia is a high level of cholesterol and/or triglycerides or a low level of high-density lipoprotein (HDL) cholesterol. Lifestyle, genetics, disorders (such as low thyroid hormone levels... read more levels, which can contribute to circulation problems, can help prevent some of the complications of diabetes as well. People with diabetes who are between 40 and 75 years are given a statin Lipid-lowering drugs Dyslipidemia is a high level of cholesterol and/or triglycerides or a low level of high-density lipoprotein (HDL) cholesterol. Lifestyle, genetics, disorders (such as low thyroid hormone levels... read more therapy to lower cholesterol levels and lower cardiovascular risk. People younger than 40 or older than 75 years and with an elevated risk of heart disease also should take a statin.
Another common problem in people with diabetes is gum disease (gingivitis Gingivitis Gingivitis is a mild form of periodontal disease characterized by inflammation of the gums (gingivae). Gingivitis results most often from inadequate brushing and flossing but may result from... read more ), and regular visits to the dentist for cleaning and preventive care are important.
Did You Know...
Prevention of hypoglycemia
One of the challenges of trying to strictly control the levels of glucose in the blood is that low blood glucose levels (hypoglycemia Hypoglycemia Hypoglycemia is abnormally low levels of sugar (glucose) in the blood. Hypoglycemia is most often caused by medications taken to control diabetes. Much less common causes of hypoglycemia include... read more ) may occur with some commonly used antihyperglycemic medications (such as insulin or sulfonylureas). Recognizing the presence of low blood glucose is important because treatment of hypoglycemia is an emergency. Symptoms may include hunger pangs, racing heartbeat, shakiness, sweating, and inability to think clearly.
If hypoglycemia is very severe, sugar must get into the body quickly to prevent permanent harm and relieve symptoms. Most of the time, people can eat sugar. Almost any form of sugar will do, although glucose works more quickly than table sugar (typical table sugar is sucrose). Many people with diabetes carry glucose tablets or glucose gel packs. Other options are to drink a glass of milk (which contains lactose, a type of sugar), sugar water, or fruit juice or to eat a piece of cake, some fruit, or another sweet food. In more serious situations, it may be necessary for emergency medical practitioners to inject glucose into a vein.
Another treatment for hypoglycemia involves the use of glucagon. Glucagon can be injected into a muscle or inhaled as a nasal powder and causes the liver to release large amounts of glucose within minutes. Small transportable kits containing a syringe or autoinjector pen filled with glucagon are available for people who frequently have episodes of low blood glucose to use in emergency situations when sugar cannot be ingested by mouth.
The following English-language resources may be useful. Please note that THE MANUAL is not responsible for the content of the resources.
American Diabetes Association: Comprehensive information on diabetes, including resources for living with diabetes
JDRF (previously called Juvenile Diabetes Research Foundation): General information on type 1 diabetes mellitus
National Institute of Diabetes and Digestive and Kidney Diseases: General information on diabetes, including on the latest research and community outreach programs
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