What’s the difference between hypoglycemia and hyperglycemia?

Hyperglycemia means that blood sugar levels are too high. It can develop if someone with diabetes doesn’t have enough insulin.

Hypoglycemia means that blood sugar levels are too low. In a person with diabetes, it can develop if they’ve taken too much insulin or haven’t eaten for a long time.

Hypoglycemia can also develop alongside alcohol use disorder and some critical illnesses. It can be life-threatening without treatment.

Doctors have clinical definitions of hyperglycemia and hypoglycemia in people with diabetes. People without diabetes may still develop low or high blood sugar in certain situations.

The two issues cause different symptoms, and this can help you tell them apart.

Below, we look at these differences, as well as the causes and treatments of each condition. 

When is blood sugar too high or low?

If you don’t have diabetes, there are no clinical guidelines about temporary changes to low or high blood sugar.

If you do have diabetes, doctors define hypoglycemia as glucose values of less than 70 milligrams per deciliter of blood (mg/dL), or 4 millimoles per liter (mmol/L).

The clinical definition of hyperglycemia, meanwhile, varies from country to country.

In the United Kingdom, the National Health Service defines it as blood sugar of over 126 mg/dL or 7 mmol/L before eating. In the United States, it’s over 125 mg/dL (6.9 mmol/L).

Blood sugar levels naturally go up and down throughout the day and after meals. Having raised blood sugar after a meal is expected — so there’s a different definition of hyperglycemia immediately after eating.

According to the NHS, having blood sugar over 198 mg/dL (11 mmol/L) after eating counts as hyperglycemia. In the U.S, it’s over 180 mg/dL (10 mmol/L) 2 hours after eating.

What’s considered high or low depends on whether you have diabetes because people with diabetes don’t metabolize glucose as efficiently. This means they’re prone to having higher blood sugar levels. 

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Signs of hypoglycemia

There are several signs of hypoglycemia, including:

  • skin becoming a paler or yellower, depending on your skin tone

  • shivering or shaking

  • tingling or numbness of the lips, tongue, or cheeks

  • sweating

  • dizziness or lightheadedness

  • headache

  • rapid heartbeat

  • irritability or anxiety

  • hunger

  • nausea

Without treatment, you may develop more severe symptoms, such as:

  • blurred or impaired vision

  • clumsiness and lack of coordination

  • feeling weak or sleepy

  • difficulty concentrating

  • confusion

  • poor sleep

  • seizures, or fits

  • collapsing or passing out

Many of these symptoms occur due to the release of epinephrine, the hormone related to your fight-or-flight response. Your body releases epinephrine when your blood sugar levels get too low.

If you’re experiencing any of these symptoms, you can find out if they’re related to hypoglycemia by checking your blood glucose levels.

To dive deeper, check out the ZOE article on low blood sugar and headaches.

Causes of hypoglycemia

Hypoglycemia is common in people with type 1 diabetes, but it can also occur in people with type 2 diabetes who are taking insulin.

Taking too much insulin or accidentally injecting insulin into the muscle are frequent causes of hypoglycemia.

The way you eat can also lead to this issue. Any of these factors can result in low blood sugar levels: 

  • not eating enough carbs

  • eating fewer carbs than usual without adjusting your insulin dose

  • skipping or delaying a meal

  • drinking too much alcohol

In addition, exercising on an empty stomach or more intensely than usual can lead to hypoglycemia.

In people who don’t have diabetes

Hypoglycemia can develop in people without diabetes, but it’s rare. Possible causes include:

  • certain medications

  • gastric bypass surgery

  • poor nutrition

  • pregnancy complications

  • certain health conditions that affect your hormone levels

To learn more, find ZOE’s hypoglycemia overview here.

What to do if your blood sugar is too low

If your blood sugar level falls too low, follow the 15-15 rule. Eat 15 g of quickly digested carbs to raise your blood sugar. This could be half a banana, half a cup of orange juice, or a tablespoon of sugar.

Retest your levels after 15 minutes. If your levels are still below 70 mg/dL (4 mmol/L), have another 15-g serving.

Repeat this until your blood glucose is back in the normal range.

Once your blood sugar levels return to normal, have a well-balanced meal or a snack with carbs, protein, and fat.

If someone passes out or otherwise isn’t able to consume carbs by mouth, they’ll need a glucagon injection to rapidly increase their blood sugar.

Glucagon is a hormone that gets your liver to release glucose into the bloodstream when your levels are low.

If glucagon isn’t available or the person is unconscious, call for emergency help.

Signs of hyperglycemia

If you have diabetes and your blood sugar is too high, you may have short-term warning signs, such as:

  • increased thirst

  • frequent urination

  • headaches

  • blurred vision

  • feeling weak or tired

If your hyperglycemia lasts without treatment, you may have: 

  • constant fatigue

  • unintentional weight loss

  • slow-healing wounds

  • recurrent infections, including thrush (a yeast infection) and bladder infections

If your blood sugar levels get really high, you may develop a complication called diabetic ketoacidosis.

Ketoacidosis occurs when you don’t have enough insulin to take blood sugar into your cells.

Instead, your liver starts to break down fat for energy, which leads to the production of acids called ketones that can build up in your blood.

Too many ketones in your blood is a life-threatening complication requiring immediate treatment.

Symptoms of ketoacidosis include:

  • shortness of breath

  • nausea and vomiting

  • abdominal pain

  • confusion

  • fruity-smelling breath

  • dry mouth

  • feeling tired or sleepy

Causes of hyperglycemia

The cause of hyperglycemia can depend on the type of diabetes you have.

In people with type 1 diabetes, hyperglycemia usually occurs when you haven’t taken enough insulin before a high-carb meal.

This can also happen in people with type 2 diabetes who take insulin.

High blood sugar levels may occur if you ate more or exercised less than you had taken insulin to account for.

Stress or illness can also lead to high blood glucose in some cases.

Many people with diabetes have a “dawn phenomenon.” This means that your blood sugar levels are high when you wake up. It stems from your body producing certain hormones while you sleep.

In people who don’t have diabetes

Hyperglycemia is less common in people without diabetes.

It can occur if you have a condition that affects your insulin or blood sugar levels, such as issues with your adrenal glands or pancreas.

What to do if your blood sugar is too high

If your blood sugar level is too high, there are several ways to bring it down. Be sure to avoid sugary or starchy foods while your level is high.

People with type 1 diabetes may take insulin to reduce their blood sugar. 

If you don’t regularly use insulin, try exercising until the level returns to normal. It’s also important to drink plenty of water.

If your blood sugar is above 240 mg/dL (13.3 mmol/L), check your urine for ketones before you consider exercising.

If you exercise while ketones are present, you could raise your blood sugar even further.

If there are ketones in your urine, contact a healthcare provider. Extremely high blood sugar levels may result in ketoacidosis, which is an emergency.


The best way to prevent hypoglycemia or hyperglycemia is through good diabetes management — with a varied, plant-rich diet and regular movement.

It’s also important to be aware of the signs of these conditions.

For hypoglycemia, check your blood sugar regularly if you have diabetes. Using either a continuous glucose monitor or a blood sugar meter will allow you to see when your levels are getting low and take action.

For hyperglycemia, be sure to take insulin and other diabetes medications at the right time and exactly as your doctor has prescribed.

Moving regularly can help you maintain healthy blood sugar levels, and changing your diet can also help. 

Limit foods and drinks that rank high on the glycemic index. These foods will have a more pronounced effect on your blood sugar.

Make sure you eat plenty of fiber and balance your carbs with protein and fat. This will help slow your digestion of carbs and limit the effect on your blood sugar.

At ZOE, we run the largest nutrition science study in the world. We know that a diet high in fiber can also benefit your gut microbiome — the community of microbes that live in your gut and have a big impact on your overall health.

With our at-home test, you can find out how healthy your gut is, along with how your blood sugar and blood fat levels respond to different foods.

Our personalized nutrition program can help you eat the best foods for you and your health goals. Learn more about how it works by taking our free quiz.


Hypoglycemia and hyperglycemia typically affect people with diabetes. Hypoglycemia is low blood sugar and hyperglycemia is high blood sugar. 

These issues cause different symptoms, and some can be serious if you don’t have the right treatment.

Knowing the symptoms of hypoglycemia and hyperglycemia can help. Both of these issues are preventable and treatable, especially when you’re aware of the early signs.