What Is Blood Sugar?

Blood glucose, or blood sugar, levels refer to the amount of simple sugar moving through your body at any given time. Glucose is the main form of energy your body uses, and everything you eat ends up breaking down to glucose for your body to use.

Without a continuous supply of glucose in your blood, your body can't carry out basic functions. Too much glucose (hyperglycemia) or too little glucose (hypoglycemia) can both cause problems.

In this article, you will learn what glucose is, what it does in your body, and why it's essential to manage it.

Person taking finger prick blood sample to test blood sugar for hypoglycemia

Science Photo Library / Getty Images

What It Is

Glucose is a simple sugar that every living organism uses for energy. Everything you consume contains some form of glucose, including:

Fats and proteins can also be broken down into glucose after they enter the body. This process is called gluconeogenesis. It's the body's way of breaking down whatever you eat into an energy source for the body to use.

How It Works

Regardless of how you consume glucose, it will enter the bloodstream once it's inside your body. Your blood will deliver glucose to all your tissues, storing any excess in specific areas like the liver and muscle tissue.

Your body needs a specific range of glucose in your blood at all times. Certain parts of the body—like the brain—are particularly sensitive to changes in your blood sugar levels. A drop in blood sugar can quickly impact how you act and think.

How Blood Glucose Is Regulated

While the food you choose to eat and how often you choose to eat impact your blood glucose level, two hormones produced in the pancreasglucagon and insulin—balance blood sugar in your body.

Glucagon regulates blood sugar when your body is in a state of fasting. Without a steady food supply, glucagon helps release a reserved form of glucose, glycogen, stored in the liver and other tissues.

Insulin, on the other hand, helps regulate your real-time blood sugar. This hormone helps glucose enter your cells as an energy source. Without insulin, blood glucose would travel through your blood—possibly accumulating at excessive levels—without reaching the tissues needing it.

What Is the Normal Blood Glucose Range?

  • The normal range for fasting blood glucose (blood glucose when you haven't eaten) should be between 70 mg/dL and 100 mg/dL (milligrams per deciliter).
  • You are considered prediabetic if your fasting blood glucose is between 100 mg/dL and 125 mg/dL. At this point, you may be able to lower your blood sugar levels with diet and lifestyle changes.
  • When your fasting blood sugar levels exceed 126 mg/dL on two or more separate tests, you will likely be diagnosed with diabetes. This may require oral or injected medications and lifestyle changes to keep your blood glucose levels within a healthy range.

When Can Blood Glucose Be a Problem?

Too much or too little glucose in your blood can cause issues. These issues can be brief if you change your diet and activity or can result in a more chronic condition, like diabetes.


If your body doesn't produce enough insulin, or your body does not respond to insulin (insulin resistance), you can develop hyperglycemia, or high blood sugar. Hyperglycemia can occur when you consume too much sugar at once, but it's more common in conditions affecting insulin regulation, like diabetes.

Some causes of hyperglycemia in people with or without diabetes include:

  • Overeating carbohydrates or sugars
  • Dehydration
  • A sedentary lifestyle
  • Certain medications, like steroids
  • Some illnesses
  • Stress


Hypoglycemia, on the other hand, is a condition that can develop if your blood glucose levels get too low. This can be caused by:

  • Not eating enough
  • Drinking alcohol on an empty stomach
  • Taking certain medications
  • Getting more exercise or physical activity than usual


Several diseases or conditions can impact glucose regulation, but diabetes is the most common. More than 11% of Americans have some form of diabetes.

The two primary forms of diabetes are classified based on how they impact blood sugar regulation, as follows:

  • Type 1 diabetes is often diagnosed at a young age and is considered an autoimmune disorder. With this kind of diabetes, your body doesn't produce enough insulin because your pancreas works improperly.
  • Type 2 diabetes is a form of diabetes that usually develops later in life due to lifestyle and diet choices. Usually, this type of diabetes develops when insulin becomes less effective at moving glucose into your cells, causing it to accumulate in the bloodstream.

Regardless of why blood sugar accumulates in the bloodstream, hyperglycemia can cause dangerous symptoms and long-term complications. High sugar levels in your blood can damage your nerves, kidneys, and other organs. At the same time, glucose cannot enter the cells that need it and essentially starve tissues in your body.

Symptoms of Blood Sugar Imbalances

Symptoms of high blood sugar, or hyperglycemia, include:

Symptoms of low blood sugar, or hypoglycemia, include:

  • Shakiness
  • Sweating
  • Nervousness
  • Anxiety
  • Irritability
  • Dizziness
  • Confusion


Blood glucose is the simple sugar that circulates in your blood, delivering energy and nutrition to all of the tissues in your body. Too much or too little blood glucose can cause immediate symptoms and chronic health problems.

A Word From Verywell

Your diet and lifestyle can impact your blood glucose levels, but so can conditions like diabetes. Talk to your healthcare provider about checking your blood glucose levels, especially if you've noticed symptoms of high or low blood sugar or if diabetes runs in your family.

Frequently Asked Questions

  • What is a normal blood sugar level?

    Normal blood sugar levels are between 70 and 100 milligrams per deciliter (mg/dL). If you've been diagnosed with diabetes, your healthcare provider will talk to you about goal ranges for your blood sugar and how to maintain them.

  • How can you reduce your blood sugar levels immediately?

    If you have diabetes, you may be prescribed medications like injectable insulin. This replaces or supplements your body's natural insulin to move glucose from your bloodstream into your cells. Watching what you eat and limiting your intake of sugars and carbohydrates can also help control your blood glucose levels.

  • What causes low blood sugar in people without diabetes?

    People without diabetes may experience low blood sugar if they've gone a long time without eating or if they dramatically increase their activity or exercise levels. Certain medications or alcohol can also lower your blood glucose.

9 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. Hantzidiamantis PJ, Lappin SL. Physiology, glucose. In: StatPearls. StatPearls Publishing; 2022.

  2. Ritter S. Monitoring and maintenance of brain glucose supply: importance of hindbrain catecholamine neurons in this multifaceted task. In: Harris RBS, ed. Appetite and Food Intake: Central Control. 2nd ed. CRC Press/Taylor & Francis; 2017.

  3. Röder PV, Wu B, Liu Y, et al. Pancreatic regulation of glucose homeostasisExp Mol Med. 2016;48(3):e219. doi: 10.1038/emm.2016.6

  4. American Diabetes Association. Blood glucose can make all the difference.

  5. Centers for Disease Control and Prevention. National diabetes statistics report.

  6. Centers for Disease Control and Prevention. What is type 1 diabetes?

  7. Centers for Disease Control and Prevention. Type 2 diabetes.

  8. Centers for Disease Control and Prevention. Diabetes complications.

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

By Rachael Zimlich, BSN, RN
Rachael is a freelance healthcare writer and critical care nurse based near Cleveland, Ohio.