Diabetes Forecast

High or Low?

Why is low blood glucose worse than high blood glucose?

Linda A. DiMeglio, MD, MPH, responds

Both high and low blood glucose come with their own risks. Neither is necessarily worse than the other.

What to Know

Hypoglycemia happens when the body’s glucose level dips too low. Symptoms of mild hypoglycemia include shakiness, sweatiness, hunger, lightheadedness, dizziness, headache, and mood swings. Severe hypoglycemia can be associated with short-term complications, including loss of consciousness, seizures, and (rarely) death. While you can treat mild hypoglycemia with rapid-acting carbohydrate (glucose tablets or juice are top options), more severe lows may require outside help, such as with injectable glucagon or intravenous glucose.

When too much glucose builds up in the blood, hyperglycemia occurs. In the short term, high blood glucose can cause fatigue, blurry vision, and dehydration. When combined with inadequate insulin, hyperglycemia can also be associated with diabetic ketoacidosis (DKA), a medical emergency requiring hospitalization, intravenous fluids, and insulin. DKA is characterized by shortness of breath, abdominal pain, vomiting, and dehydration. If left untreated, the condition leads to changes in mental status and, eventually, death.

Sustained high blood glucose over many years is associated with long-term complications of diabetes, including kidney damage, nerve damage, and eye disease.

Find Out More

With low blood glucose, the risks are generally more immediate, while chronic high blood glucose can cause harm over time. You will need to work with your provider to figure out the best target blood glucose ranges for you. You can get more information on low blood glucose at diabetes.org/hypoglycemia and on high blood glucose at diabetes.org/hyperglycemia.


Check your blood glucose as often as your doctor says is right for you—and more often if you have symptoms of low or high blood glucose, your activities vary from normal, or you are ill. Get your A1C checked regularly at your doctor’s office. By paying attention to both low and high blood glucoses you can increase the likelihood that you will stay safe, today and over many years with diabetes.



Take the Type 2
Diabetes Risk Test