Diabetes affects nearly every system in your body. High blood sugar damages blood vessels and nerves over time, creating a cascade of problems that reaches your heart, eyes, kidneys, brain, skin, and mental health. Globally, about 589 million adults were living with diabetes in 2024, and that number is projected to reach 853 million by 2050. Understanding exactly how diabetes touches each part of your body can help you recognize problems early and take them seriously.
The damage breaks down into two broad categories. Small blood vessel damage (microvascular) harms your eyes, kidneys, and nerves. Large blood vessel damage (macrovascular) accelerates heart disease and stroke. Both types of damage begin silently, often years before symptoms appear.
Heart and Blood Vessels
Cardiovascular disease is the most dangerous complication of diabetes. Adults with diabetes are nearly twice as likely to have heart disease or stroke compared to adults without it. Over time, elevated blood sugar damages the walls of your arteries, making them stiffer and more prone to plaque buildup. This process, which happens to everyone as they age, accelerates significantly with diabetes.
The result is a higher risk of heart attack, stroke, and peripheral artery disease, which reduces blood flow to the legs. High blood pressure and abnormal cholesterol levels frequently accompany diabetes, compounding the damage. This is why managing blood sugar alone isn’t enough. Blood pressure and cholesterol matter just as much for protecting your heart when you have diabetes.
Eyes and Vision
Diabetes damages the tiny blood vessels in the retina, the light-sensitive tissue at the back of your eye. This condition, called diabetic retinopathy, is the most common cause of new blindness in working-age adults. In 2021, roughly 9.6 million people in the United States were living with some form of diabetic retinopathy, and 1.84 million of those had vision-threatening disease.
The condition progresses through stages. Early on, small blood vessels in the retina weaken and leak fluid. In more advanced stages, the eye grows new, fragile blood vessels that can bleed into the eye or cause the retina to detach. Separately, fluid can build up in the central part of the retina, blurring your sharpest vision. The tricky part is that early retinopathy causes no symptoms at all. By the time you notice vision changes, significant damage may already be done, which is why annual eye exams are critical for anyone with diabetes.
Kidneys
Your kidneys filter about 50 gallons of blood every day through millions of tiny blood vessel clusters. Diabetes damages those clusters, gradually reducing your kidneys’ filtering ability. It is the leading cause of kidney failure in the United States, accounting for 44% of new cases.
Like retinopathy, kidney damage from diabetes develops quietly. Early stages produce no symptoms. As filtering capacity drops, waste products build up in your blood, and protein starts leaking into your urine. Left unchecked over years, this can progress to the point where dialysis or a kidney transplant becomes necessary. Routine blood and urine tests can catch the problem early, when treatment is most effective at slowing it down.
Nerves
Nerve damage, or neuropathy, is one of the most common and disruptive effects of diabetes. It takes several forms, each affecting different parts of your body.
Peripheral neuropathy is the most widespread type. It typically starts in the feet and legs, sometimes spreading to the hands and arms. You might feel tingling, burning, or shooting pain in your lower legs, or you might lose sensation entirely. That loss of feeling is particularly dangerous because it means you can injure your foot without realizing it.
Autonomic neuropathy damages the nerves controlling your internal organs. This can affect your heart rate and blood pressure, digestion, bladder function, sexual response, and even your ability to sense when your blood sugar drops too low. People with autonomic neuropathy sometimes experience unpredictable drops in blood pressure when standing, chronic digestive problems, or difficulty emptying their bladder.
Proximal neuropathy is rarer but can be severe, causing intense pain in the hip, buttock, or thigh, usually on one side. Focal neuropathy strikes individual nerves, most commonly in the wrist (presenting as carpal tunnel syndrome), hand, head, or torso.
Feet and Lower Limbs
The combination of nerve damage and poor circulation makes the feet especially vulnerable. When you can’t feel a blister, cut, or pressure sore on your foot, and blood flow to that area is already reduced, even a minor wound can spiral into a serious infection. Research tracking large populations found that the incidence of first-time foot ulcers was about 8 per 1,000 people with diabetes each year.
Foot ulcers that don’t heal can lead to amputation. A history of a foot ulcer is associated with a 2.4-fold increased risk of amputation or death in people with type 2 diabetes, and a 3.4-fold increase in type 1. Diabetes remains the leading cause of non-traumatic lower limb amputations. Most of these amputations are preventable with daily foot checks, proper footwear, and prompt treatment of any wound.
Skin and Wound Healing
If you’ve noticed that cuts and scrapes take longer to heal since your diabetes diagnosis, there’s a biological reason. High blood sugar disrupts the normal wound-healing process at multiple levels. Your immune cells get stuck in an inflammatory mode and fail to shift into the repair phase that actually closes wounds. At the same time, the cells that form new skin lose their ability to migrate across the wound surface effectively.
Blood vessel growth at the wound site is also impaired. New blood vessels are essential for delivering oxygen and nutrients to healing tissue, and elevated glucose interferes with the signals that trigger their formation. The net result is wounds that stay inflamed longer, close more slowly, and are more prone to infection. This is one reason why even minor skin injuries deserve careful attention when you have diabetes.
Brain and Cognitive Function
Diabetes affects the brain in ways that are still being actively studied, but the connection is clear and significant. The link works through several pathways. Heart disease and high blood pressure, both more common with diabetes, increase the risk of strokes that can cause vascular dementia. Episodes of very low blood sugar can also damage the hippocampus, the brain’s memory center.
Research published through Harvard Health tracked dementia rates across populations and found a striking pattern: for every 1,000 people examined yearly at age 70, dementia rates were 8.9 among those without diabetes. For people who had developed diabetes more than 10 years earlier, that rate jumped to 18.3, more than double. The earlier diabetes develops, the greater the long-term risk to cognitive function. Some researchers have even described Alzheimer’s disease as “type 3 diabetes” because insulin resistance in the brain appears to contribute directly to the plaques and tangles that characterize the disease.
Mental Health
Living with a chronic condition that requires daily management takes a real psychological toll. A 2021 CDC survey found that about 24% of U.S. adults with diabetes experienced moderate diabetes distress, and nearly 7% had severe distress. That translates to roughly 7.4 million people dealing with significant emotional burden from their condition.
Diabetes distress is distinct from clinical depression, though the two overlap. It includes feeling overwhelmed by the demands of managing blood sugar, worrying about complications, and experiencing guilt or frustration when numbers don’t cooperate despite your best efforts. Depression is also more common among people with diabetes, and the relationship runs both directions: depression makes it harder to manage blood sugar, and poorly controlled diabetes can worsen mood. Both are treatable, and neither is a sign of personal failure.
How the Damage Connects
What makes diabetes so far-reaching is that these complications don’t happen in isolation. Kidney damage raises blood pressure, which worsens heart disease and speeds up retinopathy. Nerve damage in the feet combines with poor circulation to create wounds that won’t heal. Cardiovascular problems feed into cognitive decline. Each complication makes the others more likely and more severe.
The common thread through all of it is blood sugar control. Sustained high glucose is what damages blood vessels and nerves in the first place. The good news is that tighter management of blood sugar, blood pressure, and cholesterol can meaningfully slow or prevent many of these complications. The damage is cumulative and time-dependent, which means every year of good control counts.