Insulin Basics

young man smiling

Diabetics need insulin therapy because they can't make their own.

Insulin therapy tries to mimic natural insulin secretion — what happens automatically in non-diabetics.

The ultimate goal of insulin therapy is to mimic normal insulin levels. Unfortunately, current insulin replacement therapy can only approximate normal insulin levels. Insulin therapy for type 2 diabetes ranges from one injection a day to multiple injections and using an insulin pump (continuous subcutaneous insulin infusion – CSII). The more frequent the insulin injections, the better the approximation of natural or normal insulin levels. Discuss with your medical provider the insulin regimen that is best for you.

On this page you will learn about:

Normal or Non-diabetic blood sugar levels and insulin release from the pancreas

Natural insulin (i.e. insulin released from your pancreas) keeps your blood sugar in a very narrow range. Overnight and between meals, the normal, non-diabetic blood sugar ranges between 60-100mg/dl and 140 mg/dl or less after meals and snacks.

See the picture below of blood sugar levels throughout the day in someone who does not have diabetes.

Normal (Non-diabetic) Blood Glucose and Insulin Levels over 24 Hours
To keep the blood glucose in a narrow range
throughout the day, there is a low steady secretion of insulin overnight, fasting and between meals with spikes of insulin at mealtimes.   Adapted: Jacobs DM Care 20:1279, 1997

To keep the blood sugar controlled overnight, fasting and between meals, your body releases a low, background level of insulin. When you eat, there is a large burst of insulin. This surge of insulin is needed to dispose of all the carbohydrate or sugar that is getting absorbed from your meal. All of this happens automatically!

More About Natural Insulin Release

Insulin is continuously released from the pancreas into the blood stream. Although the insulin is quickly destroyed (5-6 minutes) the effect on cells may last 1-1/2 hours. When your body needs more insulin, the blood levels quickly rise, and, the converse – when you need less, the blood levels rapidly fall —The situation is different when you have diabetes and are getting insulin replacement therapy. Once you have injected a dose of insulin, it is going to get absorbed into your bloodstream whether you need it or not.

At mealtime, a little insulin is released even as you are first smelling or chewing the food. This gets your body ready to receive the sugar load from the meal. Then as you eat and the food is digested, the sugar levels rise which causes a surge of insulin. The insulin levels rapidly climb and peak in about 45 minutes to 1 hour before falling back to the background or basal levels –The situation is different when you have diabetes and are getting insulin replacement therapy. You have to calculate how much carbohydrate you are going to eat and how much insulin you will need. And you have to try to mimic natural overnight, fasting (or between meals)  and mealtime insulin release with injected insulin.

See the picture below illustrating overnight, fasting and between meals insulin, and the large spikes of insulin that accompany meals.

Normal (Non-diabetic) Blood Glucose and Insulin Levels over 24 Hours
To keep the blood glucose in a narrow range overnight, fasting and between meals, there is a low basal/background secretion of insulin.  Adapted: Jacobs DM Care 20:1279, 1997
Normal (Non-diabetic) Blood Glucose and Insulin Levels over 24 Hours
To control the blood glucose while eating, there is a rapid burst of insulin at mealtimes.  These mealtime surges of insulin peak within about 45 minutes and then fall back to  the basal/background levels.  Adapted: Jacobs DM Care 20:1279, 1997

Principles of insulin replacement

When you have type 2 diabetes and don’t have enough of your own insulin, or cannot take other medications to control your blood sugar, you will need to start insulin therapy.

The insulin therapy tries to mimic natural or non-diabetic insulin secretion. There are two components of insulin therapy:

1. Background or basal insulin replacement

Background or Basal Insulin Replacement Compared with Natural, Non-diabetic Insulin Secretion
Intensive insulin therapy tries to duplicate the body’s natural pattern of insulin secretion.  With intensive insulin therapy you need a low steady amount of insulin overnight, while fasting and between meals as illustrated by the dashed line.  Adapted: Jacobs DM Care 20:1279, 1997
  • Controls glucose overnight and between meals by keeping fat in fat tissue and curbing glucose production from the liver.
  • Provides a low, continuous level of insulin.
  • Can be a long-acting insulin, which you inject once or twice daily such as the insulin analogs, insulin glargine, insulin detemir and NPH.
  • Or can be a rapid-acting insulin continuously infused under the skin, if you are using an insulin pump.
  • Represents about 50% or half of the body’s daily insulin requirements.

2. Bolus insulin replacement

Mealtime or Bolus Insulin Replacement Compared with Natural, Non-diabetic Insulin Secretion
Intensive insulin therapy tries to duplicate the body’s natural pattern of insulin secretion. With intensive insulin therapy you need a rapid surge of insulin  at mealtimes as illustrated by the golden lines  Adapted: Jacobs DM Care 20:1279, 1997

There are two kinds of bolus replacement:

Mealtime Bolus – to cover the carbohydrate in the meal or snack.

High Blood Sugar Correction Bolus – provides extra insulin to return the blood sugar back to the target level when your blood sugar is too high.

  • Bolus Insulin is usually provided by rapid-acting insulin analogs, such as insulin aspart, insulin Lyspro, and insulin glulisine or Regular insulin.
  • Represents about 10% to 20% of the daily insulin requirement at each meal, or about 50% of the body’s daily insulin needs.

Read about the different types and characteristics of insulin that are suitable for basal and bolus insulin.

Some people with type 2 diabetes need just background/basal insulin replacement, others will need just bolus insulin replacement, and still other will need both basal and bolus insulin schedules. Talk with your provider about the insulin regimen that is most suitable for you.

Learn more about :

Intensive Insulin Replacement Compared with Natural, Non-diabetic Insulin Secretion
Intensive insulin therapy tries to duplicate the body’s natural pattern of insulin secretion. With intensive insulin therapy you need a low steady level of insulin overnight, fasting, and between meals, and a rapid surge of insulin at mealtime. Adapted: Jacobs DM Care 20:1279, 1997

Self-assessment Quiz

Self assessment quizzes are available for topics covered in this website. To find out how much you have learned about Insulin Therapy, take our self assessment quiz when you have completed this section.  The quiz is multiple choice. Please choose the single best answer to each question. At the end of the quiz, your score will display. If your score is over 70% correct, you are doing very well. If your score is less than 70%, you can return to this section and review the information.

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