Insulin is a hormone produced in the pancreas that controls the amount of glucose in your bloodstream at any given moment. It also helps store glucose in your liver, fat, and muscles. Insulin regulates your body’s metabolism of carbohydrates, fats, and proteins. 

Where and what is the pancreas?

The pancreas is a leaf shaped organ tucked under the liver, close to the gallbladder, stomach and bowel.

What are the functions of the pancreas?

--> The pancreas plays a big role in digestion.

The pancreas creates and releases important hormones directly into the bloodstream. Two of the main pancreatic hormones are insulin (= lower blood sugar) and glucagon (= raise blood sugar.)

Maintaining proper blood sugar levels is crucial to the functioning of key organs including the brain, liver, and kidneys.

The pancreas contains exocrine glands that produce enzymes important to digestion. These enzymes include:

- Trypsin & chymotrypsin to digest proteins

- Amylase for the digestion of carbohydrates

- Lipase to break down fats

Where exactly is insulin made?

Insulin is made in cells of the pancreas known as beta cells. Beta cells make up about 75% of pancreatic hormone cells.

In the beta cells, insulin is created first as a big molecule called “proinsulin.” Proinsulin is broken into two pieces: insulin and C-peptide. C-peptide is important especially when determining treatment because it can be used to measure how much insulin a person is making. The more C-peptide a person has, the more insulin they are making.

The beta cells of the pancreas can sense when blood sugar levels are rising or dropping, and release insulin into the bloodstream accordingly. 

Insulin’s main function:

>>Insulin helps to transform glucose into energy.<<

Insulin’s main function is to allow other cells to transform glucose into energy throughout your body. Without insulin, cells are starved for energy and must seek an alternate source. This can lead to life-threatening complications.

After a meal, the digestive tract breaks down carbohydrates and changes them into glucose. Glucose is then absorbed into your bloodstream through the lining in your small intestine. Once glucose is in your bloodstream, insulin causes cells throughout your body to absorb the sugar and use it for energy. Insulin also helps balance your blood glucose levels. When there’s too much glucose in your bloodstream, insulin signals your body to store the excess in your liver. The stored glucose isn’t released until your blood glucose levels decrease, such as between meals or when your body is stressed or needs an extra boost of energy.

What is diabetes?

The most common problem associated with insulin is diabetes. Diabetes occurs when the body either does not secrete enough insulin or when the body no longer uses the insulin it secretes effectively.

People who have prediabetes and Type 2 diabetes usually have some level of insulin resistance.

Diabetes falls into three categories:

Type 1 diabetes (T1D) occurs when the pancreas cannot produce insulin sufficiently to meet its own needs.

The body does not make its own insulin because the insulin-producing cells of the pancreas have been damaged or destroyed. People w/ T1D must administer insulin so that the body can process glucose.

Type 2 diabetes (T2D) is more commonly associated with adults and lifestyle choices. People with type 2 diabetes will produce insulin but often not enough for their body’s needs.

The body does not respond or is resistant to the insulin produced by the pancreas. People with T2D may need to administer insulin to help them better process glucose.

Gestational Diabetes develops in pregnant women who have never had diabetes. If you have gestational diabetes, your baby could be at higher risk for health problems. Gestational diabetes usually goes away after your baby is born. However, it increases your risk for type 2 diabetes later in life. Your baby is more likely to have obesity as a child or teen and develop type 2 diabetes later in life.

What is insulin resistance?

Insulin resistance happens when cells (muscles, fat and liver cells) do not respond as they should to insulin. When your cells do not respond adequately to insulin’s signal, it results in too much glucose remaining in your bloodstream (high blood sugar). This can lead to prediabetes, which in turn can progress into full-blown type 2 diabetes.

Insulin resistance is more likely if you have too much fat stored in and around your liver and pancreas. It is linked to living with overweight or obesity, but insulin resistance can affect some people of a healthy weight/BMI. Insulin resistance can affect anyone -- you don’t have to have diabetes -- and it can be temporary (for example, using steroid medication for a brief period causes insulin resistance) or chronic. 

People who have prediabetes and Type 2 diabetes usually have some level of insulin resistance. People with Type 1 diabetes can also experience insulin resistance.

Acquired causes, meaning you’re not born with the cause, of insulin resistance include:

- Excess body fat: Scientists believe obesity, especially excess fat in your belly and around your organs (visceral fat), is a primary cause of insulin resistance. A waist measurement of 40 inches or more for men and people assigned male at birth and 35 inches or more for women and people assigned female at birth is linked to insulin resistance. Studies have shown that belly fat makes hormones and other substances that can contribute to long-term inflammation in your body. This inflammation may play a role in insulin resistance

- Physical inactivity: Physical activity makes your body more sensitive to insulin and builds muscle that can absorb blood glucose. A lack of physical activity can have opposite effects and cause insulin resistance. In addition, a lack of physical activity and a sedentary lifestyle are associated with weight gain, which can also contribute to insulin resistance.

- Diet: A diet of highly processed, high-carbohydrate foods and saturated fats has been linked to insulin resistance. Your body digests highly processed, high-carbohydrate foods very quickly, which causes your blood sugar to spike. This puts extra stress on your pancreas to produce a lot of insulin, which, over time, can lead to insulin resistance.

- Certain medications: Certain medications can cause insulin resistance, including steroids, some blood pressure medications, certain HIV treatments and some psychiatric medications.

What is the difference between insulin resistance and diabetes?

Anyone can develop insulin resistance -- temporarily or chronically. Over time, chronic insulin resistance can lead to prediabetes and then Type 2 diabetes if it’s not treated or able to be treated. Prediabetes happens when your blood glucose levels are higher than normal, but not high enough to be diagnosed as diabetes. Prediabetes usually occurs in people who already have some insulin resistance. Prediabetes can lead to Type 2 diabetes (T2D), the most common type of diabetes.

- T2D happens when your pancreas doesn’t make enough insulin or your body doesn’t use insulin well (insulin resistance), resulting in high blood glucose levels.

- As insulin resistance develops, your body fights back by producing more insulin. Over months and years, the beta cells in your pancreas that are working so hard to make insulin get worn out and can no longer keep pace with the demand for more and more insulin. Years after insulin resistance silently began, your blood sugar may begin to rise and you may develop prediabetes or type 2 diabetes. You may also develop non-alcoholic fatty liver disease (NAFLD), a growing problem associated with insulin resistance that boosts your risk for liver damage and heart disease.

Type 1 diabetes (T1D) happens when your body’s immune system attacks and destroys the insulin-producing cells in your pancreas for an unknown reason. T1D is an autoimmune and chronic disease, and people with T1D have to inject synthetic insulin to live and be healthy. While T1D is not caused by insulin resistance, people with T1D can experience levels of insulin resistance in which their cells don’t respond well to the insulin they inject.

Gestational diabetes is a temporary form of diabetes that can happen during pregnancy. It’s caused by insulin resistance that’s due to the hormones the placenta makes. Gestational diabetes goes away once you deliver your baby. Approximately 3% to 8% of all people who are pregnant people in the United States are diagnosed with gestational diabetes.

Healthcare providers often use a blood test called glycated hemoglobin (A1c) to diagnose diabetes. It shows your average blood sugar level for the past three months. People with Type 1 diabetes usually have a very high A1C and very high blood glucose levels upon diagnosis because their pancreas is producing very little or no insulin.

What is the normal range of fasting serum insulin?

Fasting Insulin: < 25 uIU/ml

References:

- History of Insulin. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3714061/

- Gestational Diabetes. https://www.diabetes.org/diabetes/gestational-diabetes

- Insulin Access and Affordability Working Group: Conclusions and Recommendations. https://care.diabetesjournals.org/content/early/2018/05/03/dci18-0019

- Sliding Scale Therapy. https://dtc.ucsf.edu/types-of-diabetes/type2/treatment-of-type-2-diabetes/medications-and-therapies/type-2-insulin-rx/sliding-scale-therapy/

- The History of a Wonderful Thing We Call Insulin. https://www.diabetes.org/blog/history-wonderful-thing-we-call-insulin

- Increasing Insulin Affordability. https://www.endocrine.org/advocacy/position-statements//increasing-insulin-affordability

- General Overview of Type 1 and Type 2 Diabetes and Resources for Patients/Families: The American Diabetes Association: https://www.diabetes.org/

- General Overview of Type 1 Diabetes and Resources for Patients/Families: The Juvenile Diabetes Research Foundation (JDRF): https://www.jdrf.org/

- Table of Non-insulin Medications: https://dtc.ucsf.edu/types-of-diabetes/type2/treatment-of-type-2-diabetes/medications-and-therapies/type-2-non-insulin-therapies/table-of-medications/

- American Diabetes Association. Get a Handle on Diabetes Medication https://diabetes.org/healthy-living/medication-treatments

- Joslin Diabetes Center. Managing Diabetes: Insulin A to Z: A Guide on Different Types of Insulin. https://www.joslin.org/patient-care/education-programs-and-classes.

- Centers for Disease Control and Prevention. Insulin Resistance and Diabetes. (https://www.cdc.gov/diabetes/basics/insulin-resistance.html)

- Freeman AM, Pennings N. Insulin Resistance. (https://www.ncbi.nlm.nih.gov/books/NBK507839/) [Updated July 10, 2021]. In: StatPearls [Internet]. Treasure Island, FL: StatPearls Publishing; 2021. 

- Lab Tests Online. Insulin Resistance. (https://labtestsonline.org/conditions/insulin-resistance) 

- National Institute of Diabetes and Digestive and Kidney Diseases. Insulin Resistance & Prediabetes. (https://www.niddk.nih.gov/health-information/diabetes/overview/what-is-diabetes/prediabetes-insulin-resistance)