Health A-Z

Medical Content Created by the Faculty of the Harvard Medical School



The symptoms of diabetes are related to high blood glucose levels. They include:

  • Excessive urination, thirst and hunger

  • Weight loss

  • Increased susceptibility to infections, especially yeast or fungal infections

Extremely high blood sugar levels also can lead to a dangerous complication called hyperosmolar syndrome. This is a life-threatening form of dehydration. In some cases, hyperosmolar syndrome is the first sign that a person has type 2 diabetes. It causes confused thinking, weakness, nausea and even seizure and coma.

The treatment of type 2 diabetes also can produce symptoms, when it leads to the complication of low blood sugar (called hypoglycemia). People with type 2 diabetes take medications to reduce blood sugar. But these medications may cause sugar levels to drop below normal, particularly if someone has eaten less than usual. Symptoms of hypoglycemia include:

  • Sweating

  • Trembling

  • Dizziness

  • Hunger

  • Confusion

  • Seizures and loss of consciousness (if hypoglycemia is not recognized and corrected)

You can correct hypoglycemia by eating or drinking something that has carbohydrates. This raises your blood sugar level.

Type 2 diabetes affects all parts of the body. It can cause serious, potentially life-threatening complications. These include:

  • Atherosclerosis Atherosclerosis is fat buildup in the artery walls. This can impair blood flow to the all the organs. The heart, brain and legs are most often affected.

  • Retinopathy Tiny blood vessels at the back of the eye become damaged by high blood sugar. Caught early, retinopathy damage can be minimized by tightly controlling blood sugar and using laser therapy. Untreated retinopathy can lead to blindness.

  • Neuropathy This is nerve damage. The most common type is peripheral neuropathy. The nerves to the legs are damaged first, causing pain and numbness in the feet. This can advance to cause symptoms in the legs and hands. Damage to the nerves that control digestion, sexual function and urination can also occur.

  • Foot problems Sores and blisters on the feet occur for two reasons:

    • If peripheral neuropathy causes numbness, the person will not feel irritation in the foot. The skin can break down and form an ulcer.

    • Blood circulation can be poor, leading to slow healing. Left untreated, a simple sore can become infected and very large.

  • Nephropathy Damage to the kidneys. This is more likely if blood sugars remain elevated and high blood pressure is not treated aggressively.

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From Health A-Z, Harvard Health Publications. Copyright 2007 by the President and Fellows of Harvard College. All rights reserved. Written permission is required to reproduce, in any manner, in whole or in part, the material contained herein. To make a reprint request, contact Harvard Health Publications. Used with permission of StayWell.

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