March 2022: All About Insulin (Part 1)

March 2022: All About Insulin (Part 1)

ViatrisWe are pleased to present the first in a three-part series on insulin sponsored by Viatris and written by Amy Hess Fischl, MS, RD, LDN, BC-ADM, CDCES. Content is provided for information only; please consult with your health care provider before making changes to your diabetes management.

Depending on who you talk to, the term “insulin” has different connotations. One thing is for certain, it is an essential medication that we need to live.

What Is Insulin?
Insulin is a hormone created by the pancreas that controls the amount of glucose in the bloodstream at all times. It also helps store glucose in the liver, fat, and muscles and regulates the body’s metabolism of carbohydrates, fats, and proteins.

Without proper pancreas (and insulin) function, the body cannot store glucose in the muscles or liver, nor can it make fat. Instead, the fat breaks down and produces ketones, an acidic by-product of fat. If the levels of these acids grow too high, the imbalance can lead to diabetic ketoacidosis, which can be fatal.

In a person without diabetes, when food is eaten, blood glucose levels rise, and the pancreas releases insulin. The insulin then attaches to that glucose and makes it ready to be used as fuel for the brain, muscles, and nerves or stored as energy for later use.

When the pancreas can no longer function the way it used to, blood glucose levels may rise dangerously high without added insulin.

Why is Insulin Needed?
If your body doesn’t make insulin, you are eventually diagnosed with type 1 diabetes. Type 1 used to be called juvenile diabetes, but new estimates show that as many as half of people with type 1 diabetes are not diagnosed until adulthood. On the other hand, if your body doesn’t use insulin properly, you may be diagnosed with type 2 diabetes.

While people with type 1 diabetes need to take insulin to survive, many people with type 2 may also require insulin. It is commonly thought that the transition to insulin in type 2 diabetes is tantamount to failure in adequately managing the condition. This is NOT true. Type 2 diabetes is a progressive condition, meaning that the pancreas slowly stops making the amount of insulin required. It is not unusual that those with long-standing type 2 diabetes – 10 or more years – may benefit from insulin use.


What Are the Different Types of Insulin?
Insulin is characterized by how fast it works. But I live by the phrase “Your Diabetes May Vary.” The insulin action estimations below give a general idea of what to expect, but glucose monitoring is the best method to identify how each insulin works. Insulin action is described using the following terms:

  • Onset - the length of time before insulin hits your bloodstream and begins to lower blood glucose.
  • Peak - the time during which insulin is at its maximum effectiveness at lowering your blood glucose levels.
  • Duration - the length of time insulin continues to lower your blood glucose levels.

These are the five main types of insulin that healthcare providers prescribe:

  1. Short-Acting Insulin - reaches your bloodstream within 30 to 60 minutes of injection. It peaks 2 to 4 hours later and lasts for 6 to 8 hours.
  2. Rapid-Acting Insulin - begins to affect blood glucose 5 to 15 minutes after injection. It peaks in about 1 to 2 hours and continues to work for 3 to 5 hours.
    There is currently one ultra-rapid-acting insulin (Afrezza) available that is inhaled instead of injected. It starts to work about 12 to 15 minutes after being inhaled, peaks about 1 hour later, with a duration of 2 ½ to 3 hours. Dosing with Afrezza is slightly different than injected rapid-acting – most people find they need 1 ½ to 2 times more Afrezza than their injected rapid-acting insulin due to how it is absorbed.
  3. Intermediate-Acting Insulin - includes NPH insulin (neutral protamine hagedorn) which affects glucose for 10 to 12 hours. A protamine is a type of protein that slows the action of this insulin.
  4. Long-Acting Insulin - enters the bloodstream 1 to 2 hours after injection and may be effective for over 24 hours. An advantage to long-acting insulin is there is no pronounced peak like short- or rapid-acting insulin, and it is meant to work more like typical pancreatic insulin. There are some newer “ultra” long-acting insulins available that were originally meant to be taken every other day or weekly. What was found was that they did not last as long as expected, but their duration was at least 24 hours, which meant that many people who needed to take two doses of long-acting could use these new versions and dose once daily.
  5. Premixed Insulin - contains a mix of rapid- or short-acting insulin combined with an intermediate-acting insulin. The downside of mixed insulin is the inability to adjust the dose based on glucose level and meal composition. For mixed insulin to have the same effect every day, the individual using it should maintain similar meals and activity….which is not very realistic.


Type Products available Onset Peak Duration To assess if dose is correct
Short Novolin Regular
Humulin Regular
30-60 min 2-4 hours 6-8 hours 2-4 hours after dose
Rapid Admelog

5-15 min




**within 12-15 min

1-2 hours




**1 hour

3-5 hours




** 2 ½ - 3 hours

1-2 hours after dose




*** 45-60 minutes after dose

Intermediate Humulin NPH
Novolin NPH
1-2 hours 6-10 hours 18-24 hours 6-10 hours after dose
Long Basaglar
1-2 hours “flat” – 8-10 hours 18-24 hours 8-10 hours after dose
Ultra Toujeo
30-90 min “flat” – may impact glucose 8-10 hours 24-42 hours 8-10 hours after dose
Premixed Humalog 75/25
Novolog 70/30
Novolin 70/30
Humulin 70/30
Humulin 50/50

10-20 min

30 min

30 min-4 hours

2-5 hours

16-20 hours

up to 24 hours

2 hours and 8-10 hours after dose

2-4 hours and 8-10 hours after dose


Amy Hiss FischlAmy Hess Fischl, MS, RD, LDN, BC-ADM, CDCES, is an advanced practice dietitian and diabetes care and education specialist at the University of Chicago within the departments of pediatric and adult endocrinology. She speaks internationally on all diabetes topics, especially meal plan options for type 1 diabetes, insulin pumps, and continuous glucose monitors. She is actively involved in the American Diabetes Association, the Academy of Diabetes Care and Education Specialists, and the Academy of Nutrition and Dietetics, as well as several international groups for diabetes and pre-diabetes. She was named 2018 IL AADE Diabetes Educator of the Year and also received the 2018 Pan Arab Congress on Diabetes Award of Excellence for her contributions to diabetes care and education. Her dream vacation always includes diving with sharks.