What are hyperglycemia and hypoglycemia?

Low blood sugar (glucose) levels, called hypoglycemia, can cause fatigue and even fainting. Hypoglycemia is more common in people with diabetes and can be caused by too much medication, not eating enough, or exercising too much.

The opposite effect, hyperglycemia (high blood sugar levels), occurs during times of stress or poorly controlled diabetes. If left untreated, high blood sugar can damage organs throughout the body.

Blood sugar is regulated by the pancreas, a long gland in the abdomen. The pancreas produces a hormone called insulin, which helps cells absorb blood sugar.

Insulin helps convert the food you eat into energy your body can use. If your body does not produce insulin or becomes resistant to the effects of insulin, you may experience blood sugar problems.

Types of hyperglycemia and hypoglycemia

The pancreas maintains the flow of glucose between the blood and cells. In diabetes, the flow is out of balance and either does not produce insulin (type 1 diabetes) or does not respond to insulin (type 2 diabetes).

Type 1 diabetes is an autoimmune disease that is usually diagnosed early in life, whereas type 2 diabetes takes time to develop. The early stage of type 2 diabetes is called prediabetes.

gestational diabetes

Symptoms of type 2 diabetes, a condition called gestational diabetes, can occur during pregnancy. Gestational diabetes usually goes away after childbirth, but indicates a higher risk of developing diabetes in the future.


Early symptoms of high blood sugar can go unnoticed, especially in the case of type 2 diabetes. In type 1 diabetes, however, elevated blood sugar can quickly turn into a dangerous condition called ketoacidosis.

Hypoglycemia can also be life-threatening for people with diabetes. Here’s what you can expect from episodes of hyperglycemia and hypoglycemia.

high blood sugar

Early symptoms of hyperglycemia include:

  • blurred vision
  • Frequent urination (urinating)
  • high blood sugar
  • Increased thirst and hunger

Hyperglycemia can make you feel weak and tired. Slow-healing wounds and sores, vaginal or skin infections, and weight loss can also be attributed to chronically elevated blood sugar levels.

ketoacidosis symptoms

Ketoacidosis can cause:

  • deep breathing or hyperventilation
  • dehydration
  • Heartbeat
  • Unusual fruity smell on breath (acetone breath)
  • Vomit


Symptoms of hypoglycemia can start small and quickly develop into a health crisis. Symptoms of low blood sugar can vary, but are most dangerous for people with type 1 and type 2 diabetes.

Low blood sugar can cause:

  • anxiety or nervousness
  • blurred or impaired vision
  • skin discoloration (pale)
  • Puzzled
  • coordination problems, clumsy
  • dizzy
  • fast heartbeat
  • headache
  • hunger
  • irritability or impatience
  • low energy
  • nausea
  • have nightmares or cry during sleep
  • Seizures
  • sleepy
  • shake
  • sweating, chills, and clamminess
  • Tingling or numbness in the lips, tongue, or cheeks


The causes of high blood sugar and low blood sugar vary.

high blood sugar

A few different conditions produce high blood sugar, but in prediabetes or type 2 diabetes, the main reason is poor insulin sensitivity. Unlike type 1 diabetes, which does not produce enough insulin, type 2 diabetes is often characterized by high insulin levels.

The body may overproduce insulin. As a result, cells become insensitive to it, which means it can’t do its job of lowering high blood sugar.

Blood sugar can rise after a meal, especially if that meal contains simple carbohydrates. Sugar-sweetened beverages are especially prone to raising blood sugar because there is no fiber, fat, or protein to slow digestion.

Once sugar is broken down and released into the bloodstream, insulin is released to push it into cells for quick energy or storage. When insulin is not working well, blood sugar stays high in the blood until it is eventually filtered out by the kidneys.

Other causes of high blood sugar include:

  • Dawn phenomenon caused by hormones produced in the early morning
  • emotional stress
  • gestational diabetes
  • illness, such as a cold or infection
  • Insufficient dose of diabetes medication
  • Disorders affecting the pancreas or endocrine system (such as pancreatitis or Cushing’s syndrome)
  • steroids or other drugs
  • surgery or trauma


Hypoglycemia can be caused by taking too much insulin or diabetes medication, or if you eat less than usual after taking your diabetes medication.

Just as eating too many carbohydrates can lead to elevated blood sugar, eating too few carbohydrates or skipping meals and delaying meals (especially after taking insulin or medication) can lead to low blood sugar.

Intense physical activity can also cause hypoglycemia because your muscles use the sugar in your blood to fuel movement. Additionally, alcohol disrupts blood sugar balance and may mask the early symptoms that lead to hypoglycemia.


Hyperglycemia can be detected in the fasting state or after meals.

A fasting blood glucose level above 125 mg/dL indicates diabetes. Usually, a fasting blood test is done first in the morning after an overnight fast (meaning not eating for 8 hours). Fasting levels between 100 mg/dL and 125 mg/dL are borderline high and may indicate prediabetes.

Blood sugar rises after meals. One to two hours after eating, blood sugar should fall back to 180 mg/dL or lower. Hyperglycemia above 180 mg/dL.

Another way to track high blood sugar is the hemoglobin A1C test. Hemoglobin A1C reflects average glycemic control over the past three months. In percentage terms, A1C levels between 5.7% and 6.4% are a sign of chronic hyperglycemia, which may indicate prediabetes. A reading of 6.5% or higher indicates diabetes.

Hypoglycemia is usually diagnosed when blood sugar falls below 70 mg/dL. Not everyone shows symptoms at this level, and some people show symptoms before their blood sugar drops this low. Severe hypoglycemia can cause neurological symptoms such as confusion and drowsiness.


Treatment varies for hyperglycemia and hypoglycemia.

high blood sugar

Hyperglycemia can be treated immediately with exercise or medication, or long-term with dietary changes and weight loss. If lifestyle changes are unsuccessful, your healthcare provider may recommend starting or adjusting your treatment plan.

If your blood sugar is above 240 mg/dL, you may be advised to check for ketones and postpone exercise.


Fast-acting carbohydrates can reverse low blood sugar in minutes. Sugary foods that don’t contain fat or protein are quickly converted to sugar, which lowers blood levels. Glucose tablets or gels, fruit juices, regular soft drinks, honey and sugary candies are some examples.

Once consumed, blood sugar should be rechecked within 15 minutes and if it does not rise above 70 mg/dL. A more balanced snack or meal can help maintain a stable blood sugar if it’s moving in the right direction.

With very low blood sugar, most people do not have the ability to treat themselves. A drug called glucagon can be given by injection. Glucagon forces the liver to release blood sugar, quickly restoring the blood to safe levels.

Working with your healthcare provider will help you avoid sudden increases and decreases in blood sugar that require emergency treatment.


Untreated hyperglycemia can damage nerves, blood vessels, tissues and organs. High blood sugar increases the risk of heart attack and stroke, as well as blindness and kidney disease.

Fortunately, regular blood sugar monitoring and A1C testing can adjust your treatment plan and avoid the negative long-term effects of high blood sugar (while also preventing dangerously low blood sugar).


Blood sugar fluctuations can be frightening and frustrating. Finding others with similar difficulties can make it easier to cope with a diabetes diagnosis. Ask your provider about type 1, type 2, or gestational diabetes group education to learn more about your condition and get tips from those who have it.

With some trial and error and the support of your healthcare team, managing your blood sugar doesn’t have to feel overwhelming.