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Complications of Diabetes Mellitus


Erika F. Brutsaert

, MD, New York Medical College

Reviewed/Revised Oct 2023 | Modified Nov 2023
Topic Resources

People with diabetes mellitus have many serious long-term complications that affect many areas of the body, particularly the blood vessels, nerves, eyes, and kidneys.

There are two types of diabetes mellitus:

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 Diabetes Complications

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:

Types of Diabetes Complications

Blood vessel complications in diabetes

Infections 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 Candidiasis . 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 Diabetic Retinopathy ). 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.

Diabetic Retinopathy

Liver damage in diabetes

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 Dialysis 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 Kidney Transplantation . 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).

Diabetic Nephropathy

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 Foot care ). 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

Proper care of feet and regular eye examinations can help prevent or delay the onset of complications of diabetes.

Did You Know...

  • People who strictly control their blood glucose levels may be able to minimize or delay diabetes complications.

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 professionals 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.

More Information

The following English-language resources may be useful. Please note that THE MANUAL is not responsible for the content of the resources.

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