What Is Insulin?

An important hormone with roles in diabetes and metabolism

Insulin is a hormone produced by the pancreas to help metabolize food and use it for energy throughout your body. This is a key biological function. A problem with insulin can have widespread effects on any or all of your tissues, organs, and systems.

Insulin is critical to your overall health and survival. Problems with insulin production or function can result in hypoglycemia (low blood sugars), hyperglycemia (high blood sugars), and diabetes.

prediabetes and metabolic syndrome

Verywell / Ellen Lindner

If you have any type of diabetes, learning how insulin works in the body can help clarify why taking daily insulin shots or wearing an insulin pump or patch may be a key aspect of your treatment plan.

This article discusses the relationship between insulin, blood sugar (glucose), and diabetes. It also covers how your body makes insulin and ways your health can be affected if you have too little or too much of it in your bloodstream.

How Insulin Is Made

Insulin is produced by the pancreas, a gland-like organ nestled in the curve of the duodenum (the first part of the small intestine), just behind the stomach. The pancreas functions both as an exocrine gland and an endocrine gland.

The exocrine function of the pancreas is to help with digestion. The endocrine function of the pancreas is to produce insulin and another hormone called glucagon that helps regulate blood sugar. The pancreatic cells that produce glucagon are called alpha cells.

Insulin is produced by specialized beta cells in the pancreas, which are clustered into groups called islets of Langerhans, or islets for short. A healthy adult pancreas has approximately one million islets, composing about 5% of the entire organ.

How Insulin Works

Insulin is the energy-storage hormone. After a meal, it helps the cells use carbs, fats, and protein as needed, and store what's left (mainly as fat) for the future.

The body breaks these nutrients down into sugar molecules, amino acid molecules, and lipid molecules, respectively. The body also stores and reassembles these molecules into more complex forms.

Carbohydrate Metabolism

Blood sugar levels rise when most foods are consumed, but they rise more rapidly and dramatically with carbohydrates. The digestive system releases glucose from foods and the glucose molecules are absorbed into the bloodstream. The rising glucose levels signal the pancreas to secrete insulin to clear glucose from the bloodstream.

To do this, insulin binds with insulin receptors on the surface of cells, acting like a key that opens the cells to receive glucose. Insulin receptors exist on almost all tissues in the body, including muscle cells and fat cells.

Insulin receptors have two main components:

  • The exterior portion extends outside the cell and binds with insulin.
  • The interior portion of the receptor signals the cell to dispatch special proteins called glucose transporters, which receive and carry glucose across the cell. As blood sugar and insulin levels decrease, the receptors empty and the glucose transporters go back into the cell.

When the body is functioning normally, the glucose derived from ingested carbohydrates gets cleared rapidly through this process. However, when there's no insulin or very low levels of insulin, this doesn't happen, leading to high blood glucose levels.

Excess blood sugar also happens when cells aren't able to use insulin properly—what's known as insulin resistance.

This can be caused by a problem with the shape of the insulin (preventing receptor binding), not having enough insulin receptors, signaling problems, or glucose transporters not working properly.

Insulin resistance can also occur as a result of excess body fat.

Fat Metabolism

Insulin has a major effect on fat metabolism. After a meal, insulin causes "extra" ingested fats and glucose to be stored as fat for future use. Insulin also plays a key role in liver function and fat cells.

Liver Function

Insulin stimulates the glycogen creation from glucose and its storage in the liver. High insulin levels cause the liver to get saturated with glycogen. When this happens, the liver becomes unable to store more.

Then, glucose is instead used to create fatty acids that are converted into lipoproteins and released into the bloodstream. These break down into free fatty acids and are used in other tissues. Some tissues use these to create triglycerides.

Fat Cells

Insulin stops fat from breaking down and prevents triglycerides from breaking down into fatty acids. When glucose enters these fat cells, it can be used to create a compound called glycerol.

Glycerol can be combined with excess free fatty acids from the liver to make triglycerides, which can then build up in the fat cells.

Protein Metabolism

Insulin helps the amino acids in protein to enter cells. Without adequate insulin production, this process is hindered, making it difficult to build muscle mass.

Insulin also makes cells more receptive to potassium, magnesium, and phosphate. Known collectively as electrolytes, these minerals help conduct electricity within the body. In doing so, they influence:

  • Muscle function
  • Blood acidity
  • The amount of water in the body

An electrolyte imbalance can be worsened by high blood sugar levels as this can cause excessive urination (polyuria), which makes you lose more water and electrolytes.


Insulin production is part of an endocrine process in the liver that controls blood sugar. Insulin helps the body break down fats, carbohydrates, and proteins from food to be used for energy.

Insulin resistance develops when cells in your muscles, fat, and liver are unable to use insulin properly, resulting in high blood sugar.

Associated Conditions

Several conditions are related to problems with insulin use or production, including diabetes, hypoglycemia, and hyperglycemia.


Diabetes comes in three forms, each with a different cause of high blood sugars.

  • Type 1 diabetes: An autoimmune condition in which the pancreas stops producing insulin. Treatment requires insulin supplementation. This chronic condition usually begins in childhood.
  • Type 2 diabetes: Involves inadequate insulin production and/or insulin resistance. Treatment may involve insulin supplementation, dietary changes, regular exercise, and medications. This chronic condition usually begins in adulthood.
  • Gestational diabetes: Temporary insulin resistance caused by pregnancy hormones that goes away once the pregnancy ends. Treatment may involve insulin supplementation, dietary changes, and regular exercise.


Hypoglycemia is low blood sugar. People with diabetes are especially susceptible, but it can happen in those without diabetes as well. Hypoglycemia is a potentially dangerous condition with symptoms including:

  • Shakiness
  • Sweating
  • Hunger
  • Headache
  • Blurred vision
  • Sleepiness
  • Dizziness
  • Confusion or disorientation
  • Irritability
  • Combativeness
  • Difficulty concentrating
  • Weakness
  • Irregular heartbeat

More serious symptoms of hypoglycemia are:

  • Inability to eat or drink
  • Seizures or convulsions
  • Unconsciousness

Hypoglycemia is commonly a side effect of diabetes medications, especially those classified as sulfonylureas and meglitinides. The risk of hypoglycemia while taking these medications increases if you:

  • Eat significantly less than usual
  • Get significantly more physical activity than usual
  • Drink too much alcohol without enough food
  • Get sick

Checking your blood sugar levels frequently and sticking to your diet and exercise regimen can help you avoid diabetes-related hypoglycemia.

Other causes of hypoglycemia include:

  • Impaired digestion due to stomach surgery or rare enzyme deficiencies
  • Medications including aspirin, sulfa antibiotics, pentamidine, and quinine
  • Binge drinking
  • Serious illnesses involving the liver, kidneys, or heart
  • Low levels of hormones including cortisol, glucagon, epinephrine, or growth hormone
  • Pancreatic tumors


Hyperglycemia is high blood sugar. The most common cause of hyperglycemia is diabetes, but it can also be caused by:

  • Infections
  • Certain medications
  • Hormone imbalances
  • Severe illnesses

Symptoms of hyperglycemia include:

  • Increased hunger and/or thirst
  • Blurred vision
  • Frequent urination
  • Headache
  • Fatigue
  • Unintended weight loss
  • Vaginal infections
  • Skin infections
  • Slow wound healing

In someone with type 1 diabetes, hyperglycemia can lead to a potentially fatal condition called ketoacidosis, in which toxic acids build up in the blood. Symptoms of ketoacidosis include:

  • Vomiting
  • Dehydration
  • Fruity-smelling breath
  • Labored breathing or hyperventilating
  • Rapid heartbeat
  • Disorientation, confusion
  • Coma

Untreated, ongoing hyperglycemia can lead to a lot of problems, including:

  • Damaged nerves, increasing your risk of vision problems, kidney disease, and problems with healing
  • Damaged blood vessels, increasing your risk of heart attack and stroke
  • Damage to other organs and tissues


Diabetes, hypoglycemia, and hyperglycemia are conditions related to how much insulin your body produces and how well your body uses it to control blood sugar.

Hypoglycemia and hyperglycemia are common in diabetes, but people who do not have diabetes can develop either due to underlying conditions that affect insulin.


The pancreas has two key roles: helping with digestion and producing the hormone insulin.

Your body needs insulin to keep blood sugar from getting too high or too low. It also enables cells in your liver, muscles, and fat to take up sugars from foods you eat and use them for energy.

If your body doesn't make the right amount of insulin or doesn't use insulin efficiently, you can develop health problems like diabetes, hyperglycemia, or hypoglycemia. Left untreated, these conditions can be very dangerous.

A Word From Verywell

There is no cure for insulin resistance in type 1 diabetes, but it can be managed with supplemental insulin.

For others, there are ways to help prevent problems with insulin that could lead to type 2 diabetes, like following a balanced, nutrient-rich diet, maintaining a healthy weight, exercising regularly, and quitting cigarettes if you smoke.

Take your healthcare provider's advice to heart and never underestimate the impact that lifestyle changes can have.

10 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.
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