What happens if high blood sugar goes untreated?

Within hours to days

Diabetic ketoacidosis. Without enough insulin the body burns fat, flooding the blood with acidic ketones. Vomiting, abdominal pain, deep rapid breathing, fruity breath, then confusion. Most common in type 1 diabetes but it happens in type 2, particularly during illness. It develops over hours and is a medical emergency.

Hyperosmolar hyperglycemic state. More common in older adults with type 2 diabetes. Glucose climbs — sometimes above 600 mg/dL — while fluid is lost through urine, and dehydration becomes profound. Develops over days, and carries a higher mortality than DKA.

Both are treatable. Outcomes depend heavily on how quickly someone is seen.

Over months to years

Sustained high glucose damages blood vessels — the small ones first, then the large ones.

Eyes. Diabetic retinopathy is a leading cause of preventable sight loss in working-age adults. It is silent until it is advanced, which is why annual dilated retinal screening matters even when vision seems fine.

Kidneys. Diabetic nephropathy is the leading cause of kidney failure. Also silent early — detected by a urine albumin test, not by symptoms.

Nerves. Neuropathy typically starts in the toes and works upward: numbness, burning, pins and needles, worse at night. Once established it is difficult to reverse, which is why early detection matters.

Feet. The dangerous combination is reduced sensation plus poor circulation plus slow healing. A small wound can become serious before it hurts. This is the pathway to most diabetes-related amputations, and daily foot checks are the single highest-value habit in diabetes self-care.

Heart and blood vessels. Cardiovascular disease is the leading cause of death in people with diabetes. Risk is roughly two to four times higher, and the relative increase is greater in women.

The part worth holding onto

Most of this is preventable, and the evidence for that is strong rather than aspirational. Landmark trials — DCCT in type 1, UKPDS in type 2 — showed that improving glucose control substantially reduces the small-vessel complications, and that the benefit persists for years afterwards.

Screening catches the silent problems while they are still treatable: annual retinal photographs, an annual urine albumin test, an annual foot check, and blood pressure and lipids managed alongside the glucose.

Needing medication added over time is the expected course of type 2 diabetes, not a personal failure.