Diabetes can damage nearly every organ system in the body when blood sugar stays elevated over months or years. The complications range from heart disease and kidney failure to nerve damage, vision loss, and slow-healing wounds that can lead to amputation. Adults with diabetes are nearly twice as likely to have heart disease or stroke compared to adults without diabetes, and an estimated 10 to 25 percent of people with diabetes will develop a foot ulcer during their lifetime. Understanding these complications, how they develop, and what to watch for can help you protect your health long before serious damage sets in.
How High Blood Sugar Damages the Body
Most diabetes complications trace back to the same root problem: chronically elevated blood sugar injures blood vessels. When too much glucose circulates in the bloodstream, it triggers a chain reaction inside vessel walls. Cells ramp up production of harmful molecules called free radicals, which neutralize nitric oxide, a compound your blood vessels depend on to stay relaxed and flexible. Without enough nitric oxide, vessels stiffen, narrow, and become prone to inflammation.
High glucose also causes proteins in the blood to become sugar-coated, forming what scientists call advanced glycation end products. These damaged proteins interfere with normal cell function and generate even more free radicals, creating a self-reinforcing cycle of damage. Over time, this process affects both large blood vessels (feeding the heart, brain, and legs) and the tiny capillaries that supply the eyes, kidneys, and nerves. That is why diabetes complications show up in so many different parts of the body.
Heart Disease and Stroke
Cardiovascular disease is the leading cause of death among people with diabetes. The vessel damage described above accelerates the buildup of fatty plaques inside arteries, a process that takes decades in most people but speeds up significantly with poorly controlled blood sugar. Diabetes also makes blood more likely to clot and harder for the body to dissolve those clots, which raises the risk of heart attack and stroke.
High blood sugar rarely acts alone. It tends to travel with high blood pressure, elevated cholesterol, and excess abdominal fat, a combination that compounds cardiovascular risk. Managing blood sugar is important, but so is keeping blood pressure and cholesterol in check. Many people with diabetes benefit from regular monitoring of all three.
Kidney Disease
Your kidneys filter blood through millions of tiny vessels, and those vessels are especially vulnerable to sugar-related damage. Over time, the filtering units start to leak protein into the urine, a condition doctors detect by measuring a protein called albumin. Small amounts of albumin leaking into urine (30 to 300 milligrams per day) signal early kidney damage. Amounts above 300 milligrams per day indicate more advanced disease.
The tricky part is that early diabetic kidney disease produces no symptoms at all. You won’t feel anything different until significant function has been lost. That is why annual kidney testing is recommended for everyone with diabetes. When caught early, the progression can often be slowed considerably through blood sugar control and blood pressure management. Referral to a kidney specialist at moderate stages of disease has been shown to improve outcomes.
Eye Damage and Vision Loss
Diabetic retinopathy occurs when high blood sugar damages the small blood vessels in the retina, the light-sensitive tissue at the back of the eye. In 2021, an estimated 9.6 million people in the United States were living with some form of diabetic retinopathy. Of those, about 1.84 million had vision-threatening disease.
The condition progresses through stages. In the earliest phase, tiny bulges form in retinal blood vessels. As damage worsens, some vessels close off entirely, starving parts of the retina of oxygen. In the most advanced stage, the eye grows new, fragile blood vessels that leak blood and fluid, which can cause scarring and retinal detachment. A related condition called diabetic macular edema, where fluid collects in the central part of the retina, can blur vision at any stage.
Like kidney disease, early retinopathy often causes no noticeable vision changes. An annual dilated eye exam is the only reliable way to catch it before permanent damage occurs. Treatments are effective at slowing or stopping progression when the disease is found early.
Nerve Damage
Diabetic neuropathy is one of the most common complications, and it takes several forms depending on which nerves are affected.
- Peripheral neuropathy is the most widespread type. It typically starts in the feet and toes, then may progress to the hands and arms. Symptoms include numbness, reduced ability to feel pain or temperature changes, muscle weakness, and loss of reflexes. Because you may not feel injuries to your feet, small cuts or blisters can go unnoticed and develop into serious infections.
- Autonomic neuropathy affects the nerves that control internal organs. This can cause a wide range of problems: a resting heart rate that feels too fast, difficulty controlling body temperature, bladder issues including frequent urinary tract infections, slow stomach emptying (which leads to nausea and feeling full after small meals), constipation or severe diarrhea, and sexual dysfunction in both men and women. One particularly dangerous effect is losing the ability to sense when blood sugar drops too low.
- Proximal neuropathy targets nerves in the thighs, hips, and buttocks. It is more common in people with type 2 diabetes over age 50. It usually strikes one side of the body and causes severe pain, muscle weakness, and difficulty standing from a seated position. Most people improve at least partly within 6 to 12 months.
- Focal neuropathy affects a single nerve, often in the hand, head, or torso. It comes on suddenly and usually resolves on its own over weeks to months.
Foot Problems and Amputation Risk
Foot complications deserve special attention because they result from several diabetes problems converging at once. Peripheral neuropathy numbs the feet so injuries go undetected. Poor circulation from damaged blood vessels slows healing. And a weakened immune response makes infections harder to fight off.
Diabetic foot ulcers affect an estimated 10 to 25 percent of people with diabetes at some point in their lives. These open sores, most often on the bottom of the foot, can become deeply infected and may not respond to treatment if blood flow is severely reduced. In the worst cases, amputation of a toe, foot, or part of the leg becomes necessary to prevent life-threatening infection from spreading. Daily foot checks, wearing well-fitting shoes, and getting a comprehensive foot exam every year are the most effective ways to catch problems before they escalate.
Skin Conditions
Diabetes affects the skin in ways many people don’t expect. High blood sugar creates a favorable environment for bacterial and fungal infections, and reduced circulation makes them slower to heal. People with diabetes are more prone to boils, styes, and fungal infections in warm, moist areas of the body.
A less common but distinctive condition called necrobiosis lipoidica causes yellow, reddish, or brown patches on the skin, usually on the shins. It starts as small raised bumps that can progress to larger areas of swollen, hard skin that may be itchy or painful. The condition develops when changes in fat and collagen occur beneath the skin. It is more common in women and has no cure, though early treatment can keep it from worsening.
Acute Emergencies
Not all diabetes complications develop slowly. Two emergencies can strike quickly when blood sugar spirals out of control.
Diabetic ketoacidosis happens when the body lacks enough insulin to use glucose for energy and starts breaking down fat at a dangerous rate. This floods the bloodstream with acidic byproducts called ketones. It is most common in type 1 diabetes but can occur in type 2 as well. Symptoms include excessive thirst, frequent urination, nausea, abdominal pain, fruity-smelling breath, and confusion. Without treatment, it can be fatal.
Hyperglycemic hyperosmolar syndrome is more common in type 2 diabetes. Blood sugar climbs extremely high while the body loses large amounts of fluid through urination. If fluids aren’t replaced, the blood becomes dangerously concentrated. Symptoms develop over days or weeks and include extreme thirst, dry mouth, warm skin without sweating, confusion, and eventually loss of consciousness. Both conditions require emergency medical care.
Gum Disease
Diabetes increases susceptibility to infections throughout the body, and the gums are no exception. People with diabetes face a higher risk of periodontitis, a serious gum infection that damages the soft tissue and bone supporting the teeth. The relationship goes both directions: gum disease can make blood sugar harder to control, which in turn worsens gum disease. Regular dental cleanings and good daily oral hygiene are particularly important if you have diabetes.
Screening That Catches Problems Early
The most dangerous thing about many diabetes complications is that they cause no symptoms until significant damage is done. The CDC recommends the following annual screenings for people with diabetes: a dilated eye exam (more often if eye problems are already present), a complete foot check (more often if you’ve had foot issues), and kidney function tests. Staying on schedule with these exams is one of the most effective things you can do, because treatments work best when damage is caught in its earliest stages.