What to Know About Glucose

Glucose is the body’s main source of energy. You get it mainly from carbohydrates that you eat, like sugar and grains. It is carried through your blood to the cells in your body, which use it for fuel.

The amount of glucose in your bloodstream is called blood sugar or blood glucose. Your body regulates blood glucose levels with insulin, a hormone that pulls glucose from the bloodstream and into cells to be used for energy.

Problems can occur if this process is disrupted. For example, in diabetes, your body doesn’t make enough insulin or use the hormone effectively, which leads to hyperglycemia, or high blood sugar. Low blood sugar, or hypoglycemia, can also occur. Both high and low blood sugar can lead to serious health concerns.

diabetes monitoring

vitapix / Getty Images

It’s important to consult with your medical provider about regulating high or low blood sugar levels, especially if you have diabetes.

This article explains how the body makes and uses glucose, as well as what factors impact glucose levels. It also covers normal blood glucose levels, as well as the risks associated with high or low blood sugar.

Making Glucose

Generally, glucose is released after the carbs in the food you eat is digested and processed by the stomach.

Your intestines then absorb glucose and release it through the bloodstream to your cells. Excess glucose is removed from your bloodstream, and converted to its storage form, glycogen.

In between meals or when you’re sleeping, your body has to make its own glucose to keep fueling your cells. During this time, the liver, which stores glucose in the form of glycogen, changes glycogen to glucose. This process is called glycogenolysis.

What Is Glucose Used For?

Consistent blood sugar levels in your bloodstream power your cells, maintain your energy, and ensure that your body functions properly.

Your pancreas, an organ in your abdomen, helps monitor your blood glucose levels. Your blood sugar levels rise every time carbs are digested, which signals certain cells in your pancreas to release insulin into your blood.

Insulin then guides the glucose into your fat, liver, and muscle cells so that it can be used for energy. Once glucose moves to these cells, your blood sugar levels return to a normal level between meals.

During the process where insulin helps glucose move from the bloodstream to cells, your blood sugar levels drop. The pancreas can tell when this is taking place and slows down insulin production. This, in turn, slows down the amount of glucose entering your cells.

When everything is working normally, this careful process ensures that you are getting the right amount of energy to power your cells.

One of the most important roles glucose plays is providing the main source of energy for your brain. Having too much or too little glucose can negatively impact the brain's ability to function and can lead to memory problems and poor attention, as well as other cognitive issues.

Normal Blood Glucose Levels

Ideal blood glucose levels vary depending on a person’s age, what medications they take, the status of their diabetes and how long they’ve had it, and any other conditions that may impact blood sugar.

While you should always discuss your target blood glucose levels with your healthcare provider, there are some general recommendations to keep in mind:

  • Fasting blood glucose (between meals): Normal fasting blood glucose levels are 70 mg/dL to 100 mg/dL.
  • Preprandial glucose (before a meal): Your blood sugar levels before eating for adults who are not pregnant should be 80 milligrams per deciliter (mg/dL) to 130 mg/dL, those for pregnant individuals who have gestational diabetes should be less than 95 mg/dL, and those for pregnant individuals with pre-existing type 1 or type 2 diabetes should be 70 mg/dL to 95 mg/dL.
  • Postprandial glucose (1-2 hours after a meal): For adults who aren’t pregnant, the target is less than 180 mg/dL. For individuals with gestational diabetes at one hour after a meal, the target is less than 140 mg/dL, and at two hours after a meal, it should be less than 120 mg/dL. Pregnant individuals with pre-existing type 1 or type 2 diabetes one hour after a meal should have levels of 110 mg/dL to 140 mg/dL, and two hours after a meal should be 100 mg/dL to 120 mg/dL.
  • Before physical activity: Exercise can use up energy and cause low blood sugar. In general it’s recommended that you aim for a range from 126 mg/dL to 180 mg/dL before exercise.
  • After physical activity: If your reading is below 100 mg/dL after exercise, try to consume 15 to 20 grams of carbs to raise your blood sugar. Check your blood sugar after 15 minutes, and if the reading is still below 100 mg/dL, have another serving of 15 grams of carbs. Repeat this every 15 minutes until you hit the 100 mg/dL minimum level. This is called the 15-15 rule.

If you’re monitoring your blood glucose levels and are concerned about how physical activity could affect you, consult your healthcare provider about what might be appropriate blood sugar targets.

What Can Influence Glucose Levels?

Besides diet, exercise, and how well your body produces and uses insulin, glucose levels may be impacted by many other factors, such as:

What Is the A1C Test?

An A1C test—or the HbA1C, hemoglobin A1C, glycated hemoglobin, or glycosylated hemoglobin test—is a blood test that helps monitor and diagnose diabetes. This test measures your average blood sugar levels over the past two to three months.

Risks of High Glucose

There are two types of diabetes: type 1 and type 2. In type 1 diabetes, the immune system attacks and destroys the pancreatic cells that make insulin. In type 2 diabetes, your body cannot make enough insulin or use it properly. Type 2 is the most common form of diabetes.

Diabetes can cause hyperglycemia. Blood glucose levels higher than 130 mg/dL while fasting or higher than 180 mg/dL two hours after eating indicate hyperglycemia. Additionally, a level of blood glucose higher than 200 mg/dL anytime is considered hyperglycemia.

Blood sugar levels that are too high can:

A life-threatening condition that can result from high blood sugar levels is diabetic ketoacidosis (DKA). It occurs when your body doesn’t have enough insulin to convert your blood sugar into energy and burns body fat instead. This generates ketones, which at high levels can make your blood acidic. This condition is more common in type 1 diabetes.

DKA is a medical emergency. Some symptoms of DKA include extremely dry mouth, nausea and vomiting, shortness of breath, and fruity breath.

Risks of Low Glucose

When your blood glucose levels drop below 70 mg/dL, it is considered low blood sugar. Below 54 mg/dL is considered severe low blood sugar. Individuals with diabetes, and especially type 1 diabetes, may experience low blood sugar once or twice a week.

Some individuals may experience low blood sugar while asleep. This may happen if you drink alcohol, take too much insulin, or have had a very active day.

Symptoms and risks associated with hypoglycemia include:

Severe low blood sugar can lead to more serious issues like feeling very weak, difficulty walking, and blurry vision. It can also lead to seizures or possibly a loss of consciousness.

When to See a Doctor

Reach out to your healthcare provider if you experience symptoms of hyperglycemia or hypoglycemia. It's especially important to see your healthcare provider if you are having difficulty controlling your blood sugar levels, as this could lead to more serious and even life-threatening health concerns.


Glucose is essential to helping our bodies function properly because it’s our cells’ main energy source. When the level of glucose in our blood is too high or low, various health problems can occur.

If it’s left untreated, it can affect various parts of the body, from the eyes to the kidneys. Therefore, if you have diabetes, work with your doctor to find the best plan to keep your blood sugar within the normal range. 

A Word From Verywell

It’s crucial to be aware of your blood glucose levels since having readings that are too high or too low can have a negative effect on your overall health. Because ideal blood sugar levels can vary greatly from person to person, it's best to come up with a treatment plan with your healthcare provider. Together, you can determine the best ways to keep your levels in check.

Frequently Asked Questions

  • What does high glucose mean?

    High blood glucose, or hyperglycemia, is when the body doesn’t have enough of the hormone insulin or can’t use insulin properly to move glucose into cells to be used for energy.

  • Where is glucose stored in the body?

    Once your body has used enough glucose for energy, excess glucose is converted to a form of energy known as glycogen and is stored in your liver and muscles.

  • How do you lower your glucose levels?

    There are several ways you can lower high blood sugar levels, such as exercising, adjusting your diet, and taking diabetes medication. Speak with your healthcare provider about strategies that will work best for you.

23 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. MedlinePlus. Blood sugar.

  2. Centers for Disease Control and Prevention. What is diabetes?

  3. Centers for Disease Control and Prevention. Low blood sugar (hypoglycemia).

  4. Centers for Disease Control and Prevention. Manage blood sugar.

  5. Nemours TeensHealth. Definition: glycogen.

  6. University of California San Francisco. The liver & blood sugar.

  7. ScienceDirect. Insulin secretion.

  8. University of Michigan Health. Carbohydrates, proteins, fats, and blood sugar.

  9. Kaiser Permanente. How our bodies turn food into energy.

  10. Harvard Medical School. Sugar and the brain.

  11. American Diabetes Association. The big picture: checking your blood glucose.

  12. World Health Organization. Mean fasting blood glucose.

  13. American Diabetes Association. 15. Management of diabetes in pregnancy: Standards of medical care in diabetes—2022. Diabetes Care. 2022;45(Supplement 1):S232–S243. doi:10.2337/dc22-S015

  14. American Diabetes Association. 6. Glycemic targets: Standards of medical care in diabetes—2022. Diabetes Care. 2022;45(Supplement 1):S83–S96. doi:10.2337/dc22-S006

  15. American Diabetes Association. 5. Facilitating behavior change and Well-being to improve health outcomes: standards of medical care in diabetes—2022. Diabetes Care. 2022;45(Supplement 1):S60–S82. doi:10.2337/dc22-S005 

  16. Colberg SR, Sigal RJ, Yardley JE, et al. Physical activity/exercise and diabetes: a position statement of the American Diabetes AssociationDiabetes Care. 2016;39(11):2065-2079. doi:10.2337/dc16-1728

  17. American Diabetes Association. Blood sugar and exercise.

  18. Centers for Disease Control and Prevention. 10 surprising things that can spike your blood sugar.

  19. Johns Hopkins Medicine. Conditions we treat: diabetes and hypoglycemia.

  20. National Library of Medicine. Management of diabetes and hyperglycemia in hospitalized patients.

  21. American Diabetes Association. Hyperglycemia (high blood glucose).

  22. National Kidney Foundation. Diabetes and your eyes, heart, nerves, feet, and kidneys.

  23. American Academy of Ophthalmology. What is diabetic retinopathy?

By Brian Mastroianni
Brian Mastroianni is a health and science journalist based in New York. His work has been published by The Atlantic, The Paris Review, CBS News, The TODAY Show, Barron's PENTA, Engadget and Healthline, among others.