Health problems can happen when blood glucose levels are out of the normal range. Having regular exams and tests can help find problems early and treat them.

Problems that may happen include:


Hypoglycemia is low blood sugar. It can be caused by:

  • Taking too much insulin for the amount of food that was eaten
  • Taking too much insulin to treat "fasting" blood sugar
  • Skipping a meal or eating a smaller meal without lowering the insulin dose
  • Exercising harder or longer than normal without lowering the insulin dose


Hyperglycemia is high blood sugar. It happens when a person does not have enough insulin to remove the glucose in the body. It can be caused by:

  • Taking too little insulin for the food that was eaten
  • Eating without taking any insulin
  • Eating a larger meal without adjusting the insulin dose
  • Exercising more or less than planned without adjusting the insulin dose
  • Stress from being sick or life events (insulin may need to be adjusted)

Diabetic Ketoacidosis

People with type 1 diabetes can get ketoacidosis. Sugar cannot get into cells to make energy when the body is not getting enough insulin. When this happens, the body starts breaking down stored fat for energy. The by-products of fat breakdown are ketone bodies. These are acids that build up in the blood that can cause ketoacidosis. It is caused by the same reasons as hyperglycemia. It may also be caused by taking too little insulin when sick with infection.

Diabetic Diseases of the Eyes, Kidneys, and Nerves

These diabetic diseases may happen:

  • Diabetic retinopathy can happen when high blood sugar and blood pressure harm tiny blood vessels in the retina of the eye. Other eye problems are also more common, such as cataract and glaucoma. A cataract is a cloud over the lens of the eye that makes it hard to see. Glaucoma is an increase in eye pressure that harms the eye's optic nerve.
  • Diabetic nephropathy is kidney damage that happens with diabetes. Blood passes through small filters in the kidneys. Changes in the blood vessels due to diabetes can cause harm to these filters. It gets worse over time. The filters cannot clean the blood and protein from the blood can leak into the urine. This can lead to kidney failure.
  • Diabetic neuropathy is harm to the nerves from diabetes. Having high blood sugar for many years can harm the blood vessels that bring oxygen to nerves. It can also harm the covering on the nerves. Damaged nerves may stop sending messages or they may send messages too slowly or at the wrong times. This can make it hard for a person to feel pain, heat, and cold. It can also make it harder for blood to flow. Injuries can happen and not be felt. In some people, nerve damage can lead to foot and leg amputations.

Heart Disease and Stroke

Diabetes can cause cholesterol levels to rise. This leads to narrow, clogged arteries that make it hard for the blood to carry oxygen to the body. This can lead to:


American Diabetes Association. Standards of medical care in diabetes-2019. Diabetes Care. 2019. Jan; 42 (Suppl 1):S1-193.

Diabetes mellitus type 1. EBSCO DynaMed website. Available at: Updated June 28, 2019. Accessed November 22, 2019.

Type 1 diabetes. American Diabetes Association website. Available at: Accessed November 22, 2019.

Last reviewed September 2019 by EBSCO Medical Review Board James P. Cornell, MD  Last Updated: 12/8/2020