Insulin Basics

Insulin is a vital hormone for controlling blood sugar levels and for people with diabetes, it can be life-saving treatment. Whether you’re newly diagnosed or know someone with diabetes, read about the insulin basics including how it works, the types of insulin and other key facts of this important medication.

What is Insulin

Insulin is an important hormone made by the pancreas to control blood sugar levels. When you eat, the body breaks down carbohydrates in the food into sugar, which then enters the blood as glucose.

The pancreas releases insulin into the blood to absorb the glucose into cells. The body either uses that glucose for energy or stores it in muscles or the liver as glycogen for later use.

The more carbs you eat, the more insulin the pancreas releases. This makes it a constant feedback loop between the pancreas and blood glucose levels.

How Insulin is Made

The history of injected insulin dates back to 1921, when researchers Frederick Banting and Charles Best discovered how to extract and refine insulin from the pancreas of animals.

It was first successfully used on a human in 1922 but wasn’t until the 1980s that an engineered, synthetic insulin was made that didn’t depend on animals (called “human insulin”).

Nowadays human insulin is made mostly from bacteria. The processes may differ but generally the bacteria is used to create a protein, which is then modified to create the human protein that produces insulin.

Types of Insulin

There’s two types of insulin for controlling high blood sugar, basal and bolus. They differ in in how long they’re effective, onset time and when they peak (i.e., when the insulin is the strongest).

Most people with type 2 diabetes are often prescribed an insulin regimen using a combination of both basal and bolus insulins to get blood sugar levels within a healthy range.

Basal Insulin

Basal is a long acting insulin that lowers high blood sugar over a long period of time. Depending on the manufacturer, basal insulins can be effective from 6 to over 24 hours.

For instance, two common generic basal insulins are Degludec and Detemir. Insulin Detemir can be effective for up to 24 hours after injection and insulin Degludec effective up to 42 hours after injection.

And basal insulins typically don’t have a “peak time” because they are long acting.

Bolus Insulin

Bolus is a rapid acting insulin that’s meant to lower or prevent spikes in blood sugar levels. Bolus insulins are taken before meals (sometimes called “mealtime insulin”) and have onset times of 30 minutes to as fast as 1 minute, depending on the brand.

Common generic bolus insulins are are Lispro, Aspart and Gluisine. Insulin Aspart (Novolog ) and Gluisine have onset times of 5-15 minutes and effective duration of up to 5 hours. Insulin Lispro (Lyumjev) has a very fast onset time of 1 minute and is effective for 4-5 hours.

Diabetes and Insulin Therapy

Diabetes mellitus is a condition where glucose in the blood exceeds normal or healthy levels. This is due to inadequate insulin production by the pancreas and/or the body’s inability to use insulin effectively, called insulin resistance. 

Types 1 and 2 Diabetes

The most common forms of diabetes are Type 1 and Type 2.

  • Type 1 is when the pancreas is affected by an autoimmune condition that impairs the pancreas’ ability to produce insulin.  Type 1 diabetes can occur in children as well as later into adulthood.
  • Type 2 is when the pancreas can’t produce adequate insulin because it’s been overworked after years of high blood glucose levels.  This is due to stress on the pancreas from continually producing insulin while the cells become more insulin resistant. Lifestyle choices in diet and activity level are highly associated with Type 2 diabetes. 

Insulin Treatment

Insulin is one of the most common treatments for people with Type 2 diabetes, second only to Metformin. Because the body can’t produce enough or use it efficiently, insulin therapy is used to help the body control blood sugar levels.

And diabetes treatment with insulin can include taking a combination of both basal and bolus insulin.

Common Side Effects

Weight gain is a common side effect of insulin. Insulin’s role is to absorb glucose away from the blood, which is then used for energy or stored in muscles or the liver.

But if you don’t use that glucose for energy, it stays in the muscles and becomes fat. And as that fat builds up, this leads to the weight gain that people may experience.

Other common but minor side effects include:

  • Redness or skin irritation around the injection site
  • Thicker skin around the injection side
  • Constipation

How Insulin is Used

Insulin is commonly taken by injection using an insulin syringe or insulin pen.

man inserting syringe in insulin vial

With a syringe, the insulin is taken from a vial and measured to the proper dosage. Insulin pens on the other hand contain both the insulin and needle together, and pens can be single-use or reusable.

A less common way to take insulin is by inhalation. Afrezza is a brand that makes a short acting insulin that’s taken using an inhaler. The inhaled insulin is absorbed in the lungs and bloodstream via insulin powder.

Injection Site

Insulin injections should go into the subcutaneous or fatty layer of the skin. The abdomen is the most common injection site because it’s easy to access and absorbed quickly. But insulin can also be injected in the front and side of thighs, upper and outer arms, and buttocks.

Wherever you choose to inject insulin, it’s good to rotate the injections in that area. You should avoid using the exact site repeatedly because it can get sore or lumps of fat can form, due to repeated injections (called “lipohypertrophy“).

woman injecting syringe on abodmen

Storage and Handling

Because insulin contains proteins, exposure to extreme heat or cold can damage or spoil insulin. In this case the insulin will not be as effective in lowering blood sugar levels. So consider using a portable insulin cooler, especially when traveling or being out for several hours.

Insulin should be kept away from extreme heat or cold because it can damage or spoil the proteins contained in the insulin. Spoiled or damaged insulin will not be as effective at lowering your blood sugar so it shouldn’t be used.

For unopened insulin vials or pens, manufacturers usually recommend that you store them in the fridge (between 36° – 46°F) but should not be frozen. Insulin that’s in-use should be stored in room temperature and away from sunlight or heat.

Also, be sure to know the the expiration date set by the manufacturer and don’t use the insulin if it’s expired.

Insulin FAQs

What’s the Difference Between Insulin vs Metformin?

Metformin and insulin are common treatments for type 2 diabetes but they serve different functions. Metformin is a generic drug that helps lower blood sugar levels by lowering the glucose produced by the liver and reducing glucose absorption in the intestines.

Insulin is a hormone that absorbs blood glucose into cells to either use for energy, or store in muscles or the liver for energy later.

How Long Can Insulin Be Out of the Fridge?

It’s generally recommended to store unopened insulin inside the fridge but insulin can last stored in room temperature for 28 days or more, depending on the manufacturer. Always be sure to follow the manufacturer’s specifications on storage, shelf life and expiration date of insulin.

How Many Units in a Vial of Insulin?

A typical vial contains 10 milliliters (mL) but the units depend on the concentration of the insulin, which is labeled as “U” and the number. For instance, a vial with concentration of “U-100” means 100 units per 1 mL and “U-500” means 500 units per 1 mL, and so on.

What is the Name of the Cell Type Responsible for Insulin Production?

The beta cells found in the pancreas are the endocrine cells that synthetize, store, and release insulin. In adults, beta cells release about 30–70 Units of insulin per day (depending on body weight) with half released after meals and the other half under basal conditions.1

Is Insulin Addictive?

Insulin is generally not considered to be addictive. And by improving blood glucose levels through lifestyle changes (diet and exercise), some people can reduce insulin or may no longer need it.

What is a Biosimilar Insulin?

A biosimilar insulin is a brand insulin that is can be used or prescribed interchangeably with another brand of insulin. For instance, Semglee (insulin glargine-yfgn) is a biosimilar to Lantus (insulin glargine) so a pharmacist can be prescribe one for the other.

Subscribe to get our latest straight in your inbox!

We don’t spam. Unsubscribe any time.

Leave a Reply