What to Know About Glucose

Glucose is the body’s main source of energy and is found in the carbohydrates you eat, like sugar and grains. It is carried through your blood to all of the cells in your body. The amount of glucose in your bloodstream is called blood sugar or blood glucose.

When functioning normally, your body regulates these blood glucose levels, ensuring your cells get their needed fuel, with insulin, a hormone that pulls glucose into cells to be used for energy. Insulin therefore removes glucose from your bloodstream and keeps your blood sugar levels steady.

Problems occur when this process is disrupted. For example, in diabetes, your blood sugar levels are too high because your body doesn’t produce enough insulin or use the hormone effectively. This can cause serious damage to your tissues and result in various complications.

Low blood sugar can also occur, and it similarly causes symptoms and can lead to serious complications.

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

Stay on top of your blood glucose levels

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Making Glucose

Generally, glucose comes from the carbohydrates in the food you eat after they are absorbed, digested, and converted to their simplest form. When you eat a carbohydrate-heavy food like bread, for instance, the enzymes and acids in your stomach break it down, releasing glucose.

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

Think of the liver as a reservoir for your body’s glucose levels which maintains a regular circulation of blood sugar. In between meals or when you’re sleeping, your body has to manufacture its own glucose to keep fueling your cells. During this time, the liver converts glycogen to glucose through a process called glycogenesis.

Using Glucose

It’s crucial that you have consistent blood sugar levels in your bloodstream to power your cells, maintain your energy, and ensure that your systems function properly.

Your pancreas serves as a monitor for your blood glucose. Your blood sugar levels rise every time carbohydrates are digested, which signals the beta 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.

The beta cells in the pancreas are always working in overdrive, monitoring blood sugar levels every few seconds. Once a carbohydrate-based food is digested, the beta cells immediately get to work, releasing insulin to the bloodstream.

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

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

Among the crucial roles glucose plays is providing the main source of energy for your brain. The nerve cells needed to convey information to your brain need healthy blood sugar levels for energy.

A 2013 review found that disruptions in blood glucose levels can lead to many common brain disorders. In fact, one of the early indications of Alzheimer’s disease is the reduction of cerebral glucose metabolism, with both human and animal studies revealing a shift in metabolism of glucose in brain cells tied to progression of the disease.

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 comorbid medical conditions that may impact blood sugar. Consult your primary care doctor about appropriate benchmarks for blood glucose levels throughout the day.

That being said, there are some general recommended glucose targets for before eating a meal, between meals, after eating a meal, and before and after exercise:

  • Preprandial (before a meal): Your blood sugar levels before eating for adults who are not pregnant should be 80 mg/dL to 130 mg/dL, those for pregnant women who have gestational diabetes should be less than 95 mg/dL, and those for pregnant women with pre-existing type 1 or type 2 diabetes should be 70 mg/dL to 95 mg/dL.
  • Fasting blood glucose (between meals): Normal fasting blood glucose levels are 70 mg/dL to 100 mg/dL.
  • Postprandial (after a meal): These are your blood glucose levels within an hour or two after eating. For adults who aren’t pregnant, the target is less than 180 mg/dL. For women with gestational diabetes at one hour after a meal, the target is less than 140 mg/dL, and for women with gestational diabetes at two hours after a meal, it should be less than 120 mg/dL. Pregnant women with pre-existing type 1 or type 2 diabetes one hour after a meal should have blood sugar levels of 110 mg/dL to 140 mg/dL, and those for pregnant women with pre-existing type 1 or type 2 diabetes two hours after a meal should be 100 mg/dL to 120 mg/dL.
  • Before physical activity: Exercise can use up energy and lower your blood glucose levels. This could result in hypoglycemia, or low blood sugar. 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. Again, this greatly varies from person to person, but 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 100 mg/dL after exercise, try to consume 15 grams to 20 grams of a carbohydrate to raise your blood sugar. Check your blood sugar again after 15 minutes, and if the reading is still below 100 mg/dL, have another serving of 15 grams of a carbohydrate. Repeat this every 15 minutes until you hit the 100 mg/dL minimum level. This is called the 15-15 rule.

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 for the past two to three months. If your glucose levels are regularly being monitored due to treatment for diabetes or another condition, your healthcare provider will most likely administer A1C testing at least four times each year.

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 produce insulin. In type 2 diabetes, your body cannot produce enough needed insulin or use it properly. This is the most common form of diabetes.

Diabetes can cause hyperglycemia, or high blood sugar. This means there’s too much blood glucose in your bloodstream. 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 higher than 200 mg/dL anytime is considered hyperglycemia.

Blood sugar levels that are too high can damage blood vessels throughout your body and affect different organs. The kidneys will aim to pass that excess blood glucose through urine. That’s why someone with hyperglycemia may need to urinate more than they normally would. This increases a person’s thirst as well, increasing risk of dehydration.

Hyperglycemia can also result in blurry vision, wounds that won’t heal, and skin infections. Vaginal yeast infections are more common in women with high blood sugar.

Additionally, high glucose can increase the risk of more serious conditions like heart disease, heart attack, and stroke.

Diabetic retinopathy is another potential complication. The longer you have diabetes and the less regulated your blood sugar levels are, the higher your risk is of developing this eye condition.

A serious 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 elevated levels can make your blood acidic. High levels of ketones lead to DKA, which is life threatening and needs to be treated right away. This condition is more common in type 1 diabetes.

When to See a Doctor

If left untreated, high blood sugar can lead to DKA, which requires emergency medical treatment. Some symptoms of DKA can include extremely dry mouth, nausea and vomiting, shortness of breath, and fruity breath.

Talk to your doctor right away if you start experiencing these symptoms and feel your blood sugar levels may have escalated or gone unchecked.


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 (hyperglycemia) or too low (hypoglycemia) can have a negative domino effect on your overall health. Given that what might be considered ideal blood sugar levels varies greatly person to person, devise a clear treatment plan with your healthcare provider to determine the best way to keep your levels in check and look out for any related conditions.

If you find yourself experiencing more severe symptoms of either having too much or too little blood sugar, or if you are living with diabetes and find your symptoms and overall health getting worse, make sure you contact your provider right away and update them on any changes in your health.

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. In general, blood glucose levels higher than 130 mg/dL while fasting or readings that are higher than 180 mg/dL two hours post-meal mean you have hyperglycemia.

  • Where is glucose stored?

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

  • How do you lower your glucose levels?

    There are several strategies for lowering high blood sugar levels. One is exercise. However, be sure to get a blood sugar reading beforehand. If your blood sugar is above 240 mg/dL, check your urine for ketones. If you have ketones, make sure to avoid exercise, since exercising with ketones can actually increase blood sugar levels.

    You may also want to adjust your diet. Consider working directly with a dietitian to cut out sugar-heavy foods. If diet and exercise aren’t working for you, consult with your doctor about adjusting your diabetes medications.

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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.
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