Diabetes kills primarily through cardiovascular disease, but it can also be fatal through kidney failure, acute blood sugar crises, overwhelming infections, and complications that seem minor at first, like a foot wound that won’t heal. In 2021, diabetes directly caused 1.6 million deaths worldwide, with another 530,000 deaths from diabetes-related kidney disease on top of that. High blood glucose is responsible for roughly 11% of all cardiovascular deaths globally. On average, type 1 diabetes shortens life expectancy by about 11 years, and type 2 diabetes by about 6 to 7 years.
Heart Attack and Stroke
Cardiovascular disease is the single biggest killer of people with diabetes. The mechanism starts at the walls of your blood vessels. Persistently high blood sugar generates a flood of unstable molecules called free radicals inside the cells lining your arteries. These molecules destroy nitric oxide, the chemical signal that keeps blood vessels relaxed and open. Without enough nitric oxide, arteries stiffen and narrow. At the same time, the vessel lining shifts toward producing chemicals that actively constrict blood vessels, making the problem worse from both directions.
High glucose also causes proteins in your blood to become sugar-coated (a process called glycation). These damaged proteins trigger inflammation in artery walls, attract immune cells, and accelerate plaque buildup. Over years, this leads to the same kind of arterial blockages that cause heart attacks and strokes in people without diabetes, but it happens faster, affects more vessels, and starts at a younger age. People with diabetes are also more likely to have a “silent” heart attack, one that causes little or no chest pain, because nerve damage from diabetes can blunt the warning signals your heart normally sends.
Acute Blood Sugar Emergencies
Diabetes can kill within hours or days during two distinct crises, both of which are medical emergencies.
The first is diabetic ketoacidosis, or DKA, which occurs mostly in type 1 diabetes but can happen in type 2 as well. When the body has almost no insulin, cells can’t use glucose for fuel, so the liver breaks down fat at a rapid pace. This produces acidic byproducts called ketones. As ketones flood the bloodstream, blood becomes dangerously acidic, dropping below a pH of 7.3 (normal is around 7.4). That level of acidity disrupts the chemical reactions your cells depend on to function. The brain is especially vulnerable: DKA can cause brain swelling, particularly in children, leading to coma and death if untreated.
The second crisis is called hyperosmolar hyperglycemic state, or HHS, and it’s more common in older adults with type 2 diabetes. Blood sugar climbs to extreme levels, sometimes above 600 mg/dL, pulling water out of tissues and into the bloodstream, which the kidneys then flush out. The resulting dehydration can reach a staggering 9 liters of water loss. Blood becomes thick and concentrated, blood pressure drops, electrolytes become severely imbalanced, and without aggressive fluid replacement, the end stage is coma, shock, and death. HHS has a higher fatality rate than DKA precisely because it develops more slowly and is often missed until it’s advanced.
Kidney Failure
The same vascular damage that destroys large arteries also destroys the tiny blood vessels in your kidneys. Over time, the kidneys lose their ability to filter waste from your blood. This decline is often silent for years, detected only through lab work. Once kidney function drops low enough, toxins accumulate, fluid balance fails, and potassium levels can rise to the point where they stop the heart. Diabetes is the leading cause of kidney failure requiring dialysis, and the 530,000 annual kidney disease deaths attributed to diabetes represent only the cases where kidney failure was the primary cause of death, not cases where failing kidneys contributed to a fatal heart attack or infection.
Infections and Sepsis
High blood sugar weakens the immune system in several overlapping ways. It impairs white blood cells’ ability to find and kill bacteria. It damages the antibodies that tag invaders for destruction, because those antibodies are proteins, and like other proteins in the blood, they become sugar-coated and less effective. The same inflammatory pathways that damage blood vessels also dysregulate the broader immune response, making it both weaker against invaders and more likely to spiral out of control once an infection takes hold.
This is why people with diabetes face higher mortality from common infections like pneumonia, urinary tract infections, and skin infections. When infection spreads to the bloodstream and triggers sepsis, the combination of an already-compromised vascular system and a malfunctioning immune response makes survival significantly harder. Diabetic foot ulcers are a particularly dangerous entry point: the five-year mortality rate after developing a diabetic foot ulcer is approximately 30%, and it exceeds 70% for those who require a major amputation.
Nerve Damage and Silent Cardiac Events
Diabetes gradually damages the autonomic nervous system, the network that controls functions you don’t consciously think about: heart rate, blood pressure regulation, breathing. When this system is impaired, your body loses the ability to respond appropriately to danger. One striking example is impaired breathing response to low oxygen. Normally, when your blood oxygen drops, your brain forces you to breathe harder. In some people with diabetic nerve damage, this reflex fails. Their oxygen can plummet without them feeling short of breath, leading to cardiac arrest that arrives without any warning signs.
This same nerve damage explains why heart attacks in people with diabetes are more likely to be painless. The nerves that would normally transmit crushing chest pain are too damaged to sound the alarm, so people delay seeking help, and the heart sustains more damage or stops entirely.
Dangerously Low Blood Sugar
Paradoxically, the treatment for diabetes can itself be fatal. Insulin and certain oral medications lower blood sugar, but if they push it too low, the consequences are immediate and severe. Research in the American Journal of Physiology has shown that severe hypoglycemia triggers death through two separate pathways at once: fatal heart rhythm disturbances and seizures that cause breathing to stop. In animal studies, blocking only one of these pathways wasn’t enough to prevent death. Both the cardiac and seizure pathways had to be addressed simultaneously to achieve survival, underscoring how aggressively low blood sugar attacks the body’s most essential systems.
Severe hypoglycemia is most dangerous during sleep, when warning symptoms like shakiness, sweating, and confusion go unnoticed. For people on insulin, nighttime lows are a recognized cause of what’s sometimes called “dead in bed” syndrome, where an otherwise stable person with diabetes is found deceased without any prior crisis.
How These Risks Compound Over Time
What makes diabetes so lethal is that these pathways don’t operate in isolation. Kidney disease raises blood pressure, which accelerates heart disease. Nerve damage masks the symptoms of heart attacks. A foot ulcer becomes an entry point for sepsis in someone whose immune system is already compromised. Poor circulation slows healing, giving infections more time to spread. Each complication feeds into the others, creating a web of risk that tightens over years of poorly controlled blood sugar. The common thread in nearly every pathway is sustained high glucose damaging blood vessels, nerves, and immune function simultaneously, which is why blood sugar management remains the single most important factor in determining whether diabetes shortens your life by decades or by very little at all.