Diabetes complications are the health problems that develop over time when blood sugar levels stay too high for too long. They range from nerve damage in the feet to vision loss, kidney failure, and heart disease. Most complications fall into two categories: damage to small blood vessels (affecting the eyes, kidneys, and nerves) and damage to large blood vessels (affecting the heart, brain, and legs). The good news is that keeping blood sugar closer to normal significantly slows or prevents most of them.
How High Blood Sugar Damages the Body
Persistently elevated blood sugar injures blood vessels and nerves through a combination of inflammation and oxidative stress. In small blood vessels, this damages the cells lining capillary walls. As the damage accumulates, affected tissues receive less oxygen. The body responds by trying to grow new blood vessels, but these replacement vessels are fragile and leak easily, causing swelling and further injury. This same basic process plays out in the eyes, kidneys, and nerves, which is why complications in those areas tend to develop together.
Large blood vessels suffer too. Diabetes accelerates the buildup of fatty deposits in artery walls, raising the risk of heart attack and stroke well beyond what other risk factors alone would predict. People with type 2 diabetes are roughly twice as likely to develop cardiovascular disease as people without it.
Eye Damage (Diabetic Retinopathy)
Diabetic retinopathy is the most common cause of vision loss in working-age adults. It progresses through stages, starting mild and potentially advancing to sight-threatening disease. In the early, nonproliferative stage, tiny bulges called microaneurysms form in the retina’s blood vessels. As damage worsens through moderate and severe stages, bleeding spreads across the retina, and blood vessels begin to swell and distort.
The most advanced form, proliferative diabetic retinopathy, occurs when the retina becomes starved for oxygen and the body grows new, abnormally fragile blood vessels. These can bleed into the gel-like interior of the eye and form scar tissue that pulls on the retina, potentially causing detachment and permanent vision loss. The tricky part is that early retinopathy often produces no symptoms at all. By the time you notice blurry vision or dark spots, the disease may be well advanced. This is why annual dilated eye exams are critical for anyone with diabetes.
Kidney Disease (Diabetic Nephropathy)
The kidneys filter waste from your blood using millions of tiny blood vessels. High blood sugar damages these filters over years, gradually allowing protein to leak into your urine. The earliest sign is a slightly elevated level of a protein called albumin in the urine. A urine test measuring albumin levels above 30 mg/g signals early kidney damage. Levels above 300 mg/g indicate more advanced disease.
Diabetic kidney disease often develops silently over 10 to 15 years. Without intervention, it can progress to kidney failure requiring dialysis or a transplant. High blood pressure, which commonly accompanies diabetes, accelerates the damage. Keeping both blood sugar and blood pressure under control is the most effective way to protect kidney function. Your doctor can track kidney health with a simple annual urine test and a blood test estimating how well your kidneys are filtering.
Nerve Damage (Diabetic Neuropathy)
Nerve damage is one of the most common diabetes complications, and it comes in several forms that affect different parts of the body.
Peripheral Neuropathy
This is the most familiar type, typically starting in the feet and legs and sometimes spreading to the hands and arms. It causes tingling, burning, numbness, or sharp pain. The numbness is particularly dangerous because you may not feel a cut, blister, or infection on your foot, which can lead to serious wounds that heal slowly and, in severe cases, amputation.
Autonomic Neuropathy
This type damages the nerves controlling internal organs. It can affect heart rate, blood pressure, digestion, bladder function, and sexual response. One especially concerning effect is losing the ability to feel when your blood sugar drops too low, a condition called hypoglycemia unawareness. Without the usual warning signs of shakiness, sweating, and confusion, dangerously low blood sugar can catch you off guard.
Proximal and Focal Neuropathy
Proximal neuropathy causes sudden, severe pain in the hip, buttock, or thigh, usually on one side. It’s rare but disabling. Focal neuropathy damages individual nerves, most commonly in the hand, head, or torso. Carpal tunnel syndrome, which causes pain and numbness in the wrist and hand, is one of the most common focal neuropathies linked to diabetes.
Digestive Problems and Gastroparesis
When autonomic nerve damage reaches the digestive tract, it can slow down the movement of food through the stomach, a condition called gastroparesis. Symptoms include nausea, vomiting, feeling full after only a few bites, bloating, and unpredictable blood sugar swings because food is absorbed erratically. Diagnosing it typically involves a gastric emptying scan: you eat a small meal containing a harmless radioactive tracer, and a camera tracks how quickly your stomach empties over about four hours. Gastroparesis can’t be cured, but dietary changes (smaller, more frequent meals with less fat and fiber) and medications to stimulate stomach contractions can help manage symptoms.
Heart Disease and Stroke
Cardiovascular disease is the leading cause of death among people with diabetes. High blood sugar damages artery walls, promotes inflammation, and makes blood more likely to clot. These effects stack on top of other risk factors like high blood pressure, high cholesterol, and obesity, which frequently accompany type 2 diabetes. The result is a significantly higher risk of heart attack, stroke, and peripheral artery disease, which reduces blood flow to the legs and feet.
Peripheral artery disease combined with neuropathy creates a particularly dangerous situation in the lower limbs. Poor circulation slows healing while numbness masks injuries. Together, they account for the majority of diabetes-related amputations. Checking your feet daily for cuts, blisters, or color changes is one of the simplest and most effective protective habits you can adopt.
Hearing Loss
Hearing loss is twice as common in people with diabetes compared to people of the same age without it. Even people with prediabetes have a 30% higher rate of hearing loss than those with normal blood sugar. The mechanism mirrors what happens elsewhere in the body: high blood sugar damages the small blood vessels and nerves of the inner ear. Chronically low blood sugar can also impair the nerve signals traveling from the inner ear to the brain. If you notice difficulty following conversations, frequently asking people to repeat themselves, or needing to turn the TV volume higher than usual, it’s worth getting a hearing evaluation.
Skin and Oral Health
Diabetes increases vulnerability to skin infections, slow wound healing, and several distinct skin conditions that cause darkened patches, blisters, or thickened skin. High blood sugar creates a friendlier environment for bacteria and fungi, making infections more frequent and harder to clear.
Gum disease is also significantly more common and more severe in people with diabetes. Elevated blood sugar reduces the body’s ability to fight bacterial infections in the mouth, and gum disease in turn makes blood sugar harder to control, creating a cycle that worsens both conditions. Regular dental cleanings and daily flossing matter more than most people realize.
Reducing Your Risk
The target most doctors use for blood sugar control is an A1C below 7%, though individual targets vary by age, health status, and other factors. A1C reflects your average blood sugar over the past two to three months. Lowering it meaningfully reduces the risk of every microvascular complication: eye, kidney, and nerve damage all respond to better glucose control.
Beyond blood sugar, the most impactful steps are controlling blood pressure (which protects the kidneys and cardiovascular system), managing cholesterol, staying physically active, not smoking, and keeping up with screening appointments. Annual dilated eye exams, yearly urine tests for kidney function, and daily foot checks cost little effort but catch problems early, when they’re most treatable. Complications are not inevitable. They develop over years, and at every stage, the trajectory can be slowed or even partially reversed with consistent management.