Insulin: How it works, functions, types, and insulin-related conditions

Insulin is essential for survival, and several body functions, including blood sugar regulation, are controlled by the effective balance of this hormone. 

Image of a girl injecting insulin hormone into her abdomen

Key takeaways

  • Insulin is a hormone secreted by beta cells of the pancreas. Its primary role is to help regulate blood sugar levels by enabling the cells to utilize glucose.
  • Insulin not only regulates the blood sugar level but also plays other vital roles for survival, including balancing electrolytes in the body and helping cells absorb amino acids.
  • Any problem with insulin secretion or function can result in serious medical conditions.
  • Insulin treatment and some lifestyle changes can help manage high blood sugar levels.

Insulin is an essential hormone naturally produced by the beta cells in the pancreas. It plays an important role in regulating blood glucose levels and how the body uses energy from food.

Any problem with producing insulin or how the body uses insulin can result in a high or low insulin level, which in turn can cause the blood glucose levels to be either high or low. A continuous state of high or low glucose levels may result in serious health conditions.

In this article, we will look at how the body makes insulin, what happens when there isn't enough of it, and what types of insulin one can take to supplement it.

The role of insulin in the body

Insulin is a nutrient storage hormone that plays many roles in the body, such as:

  • It helps to balance blood sugar levels by stimulating the liver, muscle, and fat cells to take up the glucose in the blood for energy, therefore lowering the blood glucose level.
  • It promotes the synthesis of glycogen. Insulin stimulates the liver and muscles to store excess glucose as glycogen. When needed, this glycogen can be converted back to glucose.
  • It promotes fat storage and prevents fat breakdown. It also encourages the production of fatty acids converted into triglycerides. The stored fat is broken down and converted to be used as a future source of energy.
  • It helps the cells absorb amino acids, promoting their production and preventing the breakdown of proteins in the cells. This is important for building muscle mass and healing wounds.
  • It balances the electrolytes in the body. Insulin helps to stimulate potassium absorption into the cells and controls the amount of fluid and sodium excreted in the urine.
  • It promotes bone formation. Insulin stimulates bone cells to form new bones, prevents bone mass loss, and encourages collagen production.
  • It promotes weight gain. After storing glucose as glycogen in the liver and muscle, insulin stores the excess sugar as fat in the fatty cells. This can result in weight gain.
  • It may be involved in improving the memory and learning capabilities of the brain.

How secreted insulin works and what it does

Insulin is mainly secreted in response to increased blood glucose levels. After eating, the food is digested, and the carbohydrates in the food are broken down and converted into glucose. This glucose enters the bloodstream, increasing the blood glucose level. 

The increase in blood glucose level stimulates the beta cells in the pancreas to release insulin. The higher the level of glucose in the blood, the higher the amount of insulin the pancreas produces.

Insulin helps the blood glucose level return to its normal level. It moves glucose into the cells, where it is used as energy, and the remaining glucose is stored as glycogen in the liver, muscle, and fat cells as a future source of energy. Once the blood glucose level returns to normal, insulin production slows down.

Aside from carbs, protein, fat, and other hormones such as estrogen, growth hormone, leptin, and melatonin can also stimulate the release of insulin. 

To balance the blood sugar level, insulin works hand in hand with another hormone known as glucagon. 

Glucagon, which is also produced in the pancreas, is released when blood sugar levels are low. It breaks down the stored glucose (glycogen) and releases it into the bloodstream to increase the blood glucose level and provide energy to the body’s cells.

Health conditions associated with insulin

Many conditions can develop when the body does not produce or use insulin as it should, and some of them can be life-threatening if they are not properly managed. Some of the conditions that are insulin-related include:

1. Insulin resistance

Insulin resistance is a condition where the body does not respond well to or effectively use the insulin it produces. This affects the movement of glucose into the cells, resulting in an increase in blood sugar levels (hyperglycemia).

To overcome the increased blood glucose levels, the pancreas continues to produce more insulin, which may result in hyperinsulinemia (an increase in insulin level).

With the increased insulin level, if the body cells continue to resist its effect, the pancreas may wear out and glucose will accumulate in the bloodstream, causing hyperglycemia (high blood glucose level). Hyperglycemia, if left unmanaged or untreated with time, leads to type 2 diabetes. 

2. Diabetes

Diabetes is a chronic health condition marked by a prolonged increase in blood sugar levels. It is caused by the cells of the body not responding to insulin (insulin resistance) or the pancreas not producing enough or any insulin at all. 

Diabetes, if left untreated, can damage nerves and organs, resulting in serious health issues such as ketoacidosis, kidney disease, cardiovascular disease, and impaired vision. 

There are two main types of diabetes.

  • Type 1 diabetes: This type of diabetes is believed to be caused by an autoimmune reaction that occurs when the immune system, instead of protecting the body, accidentally attacks the body, destroying the cells in the pancreas. This causes the body to not produce enough insulin or any insulin at all. There is currently no cure for type 1 diabetes but it can be managed by taking a daily dose of insulin. 
  • Type 2 diabetes: This is the most common type of diabetes and is most common in adults. It occurs when the body develops insulin resistance, and the pancreas cannot produce enough insulin to manage sugar levels, resulting in high blood sugar.

3. Insulinoma

Insulinoma is a rare tumor that affects the beta cells in the pancreas. It causes the pancreas to produce excess insulin. The tumor causes continuous production of insulin regardless of the blood glucose level, resulting in a low blood sugar level (hypoglycemia). Most insulinomas can be treated and even cured using treatments like surgery.

4. Polycystic ovary syndrome (PCOS)

PCOS is a common but complex hormonal disorder that affects women in their reproductive years. It is characterized by high levels of androgen (the male sex hormone), which can prevent ovulation and cause irregular or absence of menstrual periods, acne, and hirsutism (excess body hair, especially on parts of the body where there is usually little or no hair).

The exact cause of PCOs is unknown, but genetics and environmental factors may play a role. Risk factors, such as obesity and insulin resistance, are also associated with PCOS. High insulin levels can cause the ovaries to produce too much testosterone in people with this condition, which interferes with ovulation.

Types of insulin treatment

Insulin treatment is one way that people with type 1 diabetes and some people with type 2 diabetes can be treated. This therapy helps to maintain a steady blood sugar level and prevent the complications of diabetes.

There are different types of insulin regimens.  According to the American Diabetes Association (ADA), the different types can be categorized according to:

  • How quickly they work (onset)
  • when they are most effective (peak)
  • how long they last before wearing off (duration)

The main types of insulin, based on their onset, peak, and duration are: 

  • Bolus insulin
  • Basal insulin 

Bolus insulin

These are types of insulin taken at meal times, either shortly before, after, or together with the meals.

Bolus insulin acts quickly on the carbs from the meal consumed; this helps to prevent a spike in blood glucose after meals. Types of bolus insulin include:

  1. Fast-acting insulin (also known as rapid-acting insulin): This type of insulin is quickly absorbed into the bloodstream. It takes a few minutes to start working and keeps working for three to five hours, depending on the brand and dosage. It is most effective about an hour or two after taking it. 
  2. Regular or short-acting insulin: This type of insulin works similarly to rapid-acting insulin but more slowly. It takes about 30 to 60 minutes to start working and lasts 5 to 8 hours.

Regular insulin needs to be taken about 25 minutes before meals because it takes time to start working. It is most effective 2 to 4 hours after taking it.

Basal insulin

Also known as background insulin, it is a type of insulin that helps to control the blood sugar your body is releasing or moving to cells throughout the day when you are not eating. It works for a long period of time and is usually taken once or twice a day, depending on the insulin.

Types of basal insulin include the following:

  1. Intermediate-acting insulin: This type of insulin slowly enters the bloodstream, but its effect lasts longer. It is best for managing blood sugar levels between meals or overnight. The different options for intermediate-acting insulin include isophane (NPH) insulin, which takes 1 to 2 hours to start working, and pre-mixed insulin, which is a mixture of NPH with rapid-acting or regular insulin.
  2. Long-acting insulin: This type of insulin functions similarly to intermediate-acting insulin, but it gets into the blood at a slower rate. It can stabilize the blood sugar for almost the entire day, and it is usually taken once daily. It starts working between 1.5 and 2 hours, and the effect lasts for 12 to 24 hours.

Insulin comes in a liquid form, which can be clear or cloudy, depending on the type. It is available in different concentrations. The higher the concentration, the faster the rate of diffusion and adsorption. One hundred units of insulin in one milliliter of fluid (U-100) is the most common insulin concentration. To ensure you are taking the right dosage of insulin, make sure to check its concentration.

How to take insulin

Insulin can be administered by injecting it into the skin or vein using a needle (needle and syringe), pen, or a small medical device known as an insulin pump, which is attached to the body. There is also an inhalable type of insulin that is inhaled into the lungs. 

Tips for managing insulin levels and improving insulin sensitivity

Some lifestyle changes can help manage blood glucose levels and improve insulin sensitivity. They are:

  • Regular exercise: when you exercise, the muscle cells absorb glucose for energy. Regular physical activities can help increase insulin sensitivity and lower blood sugar levels. It can also promote weight loss and reduce the risk of type 2 diabetes.
  • Getting enough sleep: Sleep is important for maintaining a healthy blood glucose level. Research has shown that sleep deprivation is related to insulin resistance, obesity, and type 2 diabetes.
  • Weight loss: Having a higher body mass index within the overweight and obese range can increase the risk of insulin resistance. A review article by Aras and his associates revealed that shedding some pounds off your body weight can help improve your insulin sensitivity and prevent an increase in blood sugar levels.
  • Reduce stress: Physical or emotional stress can increase blood glucose levels. Engaging in relaxing activities such as meditation and yoga can help relieve stress and promote better sleep.
  • Eating foods that support weight and glucose management: Consuming a well-balanced, nutritious diet that is low in carbs and high in unsaturated fats and soluble fiber may help improve insulin sensitivity in people with and without diabetes.

Insulin-related issues can result in hyperglycemia or hypoglycemia,  which can cause life-threatening complications if they persist.

Severe hyperglycemia and severe hypoglycemia are serious medical emergencies that require immediate medical attention. Seek urgent medical care if you experience any of the following hyperglycemia- or hypoglycemia-related symptoms:

  • A high blood sugar reading that persists for a long time and a test that reveals the presence of ketones in urine
  • Weakness on one side of the body and a severe headache
  • Loss of consciousness
  • Confusion
  • Chest pain that spreads down the arm
  • A fever
  • Extreme thirst and frequent urination
  • Dizziness
  • Trouble breathing
  • Stomach pain, nausea, and vomiting
  • Loss of vision
  • Hallucinations
  • Difficulty speaking, seizures, unconsciousness


Insulin plays an important role in regulating various processes in the body, from promoting metabolic function, promoting the growth and development of tissues and cells, and balancing electrolytes to promoting cognitive functions.

Given its role in regulating multiple processes in the body, insulin is essential for staying alive. Any impairment in how it works can affect any or all the organs, tissues, or body systems. This increases the risk of several chronic diseases and can even result in medical emergencies.

Your overall lifestyle can affect how your body uses insulin. Lifestyle changes such as exercising, getting adequate sleep, eating healthy, and weight management can help increase insulin sensitivity and control blood glucose levels.

A doctor may advise an insulin treatment when the body is unable to produce enough insulin or use it as effectively as it should. It is important to follow your doctor's instructions on how to take the insulin, when to take it, and the insulin dose to take. 

It is also important to seek immediate medical attention if you are experiencing symptoms that may indicate a severe or persistent fluctuation in your blood glucose level.

Frequently Asked Questions (FAQs)

How does insulin cause the blood glucose level to decrease?

Insulin causes the blood glucose level to decrease and return to normal by promoting the movement of glucose from the bloodstream into the cells for energy and storing the remaining for future use in the liver, muscle, and fat.

Can blood sugar go down without taking insulin?

Although insulin is an important hormone that we cannot survive without, lifestyle modifications can help blood sugar go down without taking insulin. These modifications include exercising, getting adequate sleep, and eating foods low in carbs.

What are the common sites of injection for insulin?

The common and ideal site for injecting insulin into the body is the part that contains a significant amount of fat, such as the front or side of your thighs, your abdomen, your upper buttocks, and your upper arms.