When blood sugars are high, known as hyperglycemia, or low, known as hypoglycemia, people can experience a variety of symptoms that range from mild to serious. People with untreated symptoms can develop serious or life threatening complications.

After consuming food containing carbohydrates, the digestive system can break it down into a type of sugar called glucose, the body’s primary source of energy.

This sugar then enters the bloodstream, and the hormone insulin allows glucose to enter cells and provide them with the energy to function.

Insulin plays a vital role in regulating blood sugar. If the body is unable to produce sufficient insulin or the cells do not respond to insulin, it may have difficulty managing blood sugar levels. This can result in a person experiencing or hyperglycemia or hypoglycemia.

This article discusses the symptoms and potential complications of hyperglycemia and hypoglycemia.

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Symptoms of high blood sugar, or hyperglycemia, can include:

If a person has severe hyperglycemia, they may:

  • have an altered mental state, such as changed mood or problems with their cognitive processes
  • have focal neurologic problems, or issues with their nerves, brain, or spinal cord in a specific body area
  • go into a coma

Learn more about how high blood sugar levels feels.

If a person has untreated or uncontrolled hyperglycemia for a long time, they may develop:

  • Retinopathy: This refers to damage to the blood vessels at the back of a person’s eye. People with retinopathy may lose their vision or become blind.
  • Nephropathy: This describes the deterioration of a person’s kidney function. People with nephropathy may eventually have kidney failure.
  • Neuropathy: This is damage to a person’s nervous system. People with neuropathy may feel weakness, numbness, and pain in their hands and feet.
  • Coronary artery disease (CAD): This is the most common form of heart disease in the United States. People with CAD can have chest pains, heart attacks, or heart failure.
  • Cerebrovascular disease: This condition restricts the blood flow to a person’s brain. This can lead to brain damage or strokes.
  • Peripheral vascular disease (PVD): People with PVD have decreased blood flow to their arms, legs, and some internal organs. PVD can eventually cause a person’s tissue to die, sometimes leading to limb amputation. People with PVD can also have heart attacks or strokes.

Learn how to lower high blood sugar levels.

People with hypoglycemia have symptoms that develop quickly. Symptoms can vary from person to person. Mild or moderate symptoms may include:

  • hunger
  • being tired
  • feeling shaky
  • feeling dizzy or lightheaded
  • feeling confused or irritable
  • fast or unsteady heartbeat
  • headaches
  • not being able to see clearly
  • not being able to speak clearly

If a person has severe hypoglycemia, their blood glucose levels get very low. Symptoms of severe hypoglycemia may include:

  • losing consciousness
  • seizures
  • coma
  • inability to safely swallow food or drink

Severe hypoglycemia can be a life threatening medical emergency that requires urgent medical attention.

Learn more about the symptoms of low blood sugar.

People with mild or moderate low blood sugar can treat their symptoms quickly by consuming sources of fast-acting glucose, such as candy, fruit juice, or soda. However, severely low blood sugar can quickly cause serious health complications, such as:

  • passing out
  • seizures
  • brain damage
  • coma

In some cases, these complications can be fatal.

Learn more about how low blood sugar affects the body.

The body regulates blood sugar levels using insulin. However, certain triggers can also influence a person’s blood sugar levels.

Triggers that may raise a person’s blood sugar levels include:

Learn about blood sugar spikes with diabetes.

Triggers that can lower a person’s blood sugar levels include:

  • missing meals or not eating enough food
  • eating food with fewer carbohydrates than usual
  • drinking alcohol, especially if a person has an empty stomach
  • too much insulin due to taking too much diabetes medication
  • doing more physical activity than usual
  • being in extreme heat

People’s blood sugar levels also rise and fall naturally over the course of a day.

Learn about ideal blood sugar levels.

People can manage their blood sugar levels by:

  • exercising regularly
  • eating a healthy diet that includes plenty of fruit and vegetables
  • taking any medication as their doctor prescribes
  • eating at regular times
  • avoiding skipping meals
  • eating foods low in trans or saturated fats
  • eating foods low in sugar and salt
  • drinking water instead of juice or soda
  • limiting their alcohol intake

Learn about 12 foods that will not increase blood sugar levels.

People’s bodies normally regulate their blood sugar levels as they eat and absorb food. If a person’s body cannot regulate their blood sugar level, they may experience various symptoms of hyperglycemia or hypoglycemia. These symptoms can be mild, moderate, or severe. People with severe symptoms may require urgent medical attention.

People with constantly high or low blood sugar can develop complications over time without treatment. These complications can be serious or fatal. However, people can take simple steps to help manage and regulate their blood sugar levels and avoid complications.

Learn more about blood sugar levels and diabetes in our dedicated hub.