Insulin Basics - Type 1 Diabetes

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 1 Diabetes requires multiple injections or 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.

Normal or non-diabetic blood glucose

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

Normal insulin release

- Background insulin: To keep the blood glucose controlled overnight, fasting and between meals, your body releases a low, background level of insulin. 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.

- Mealtime Insulin:  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 glucose 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.
 

 

When you have Type 1 Diabetes

- Background insulin (Basal): The situation is different when you have Diabetes and are getting insulin replacement therapy.  You will need to inject a long acting insulin, commonly known as basal insulin, to keep the glucose controlled overnight, fasting and inbetween meals.  These are generally designed to be taken 1-2 times daily by injection or every few minutes by insulin pump.

- Mealtime insulin (Bolus): 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, how much insulin you will need and inject the mealtime/bolus insulin ideally before eating.  This type of insulin starts working in 5-15 minutes  and lasts 3-4 hours (depending on the specifice type).

Principles of insulin replacement

When you have Type 1 Diabetes, you will need to start insulin therapy because you no longer make your own insulin. The insulin therapy tries to mimic natural or non-diabetic insulin secretion. There are two components of insulin therapy.

 

1. Basal 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, insulin degludec 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 Glucose Correction Bolus – provides extra insulin to return the blood glucose back to the target level when your blood glucose is too high.
    • Bolus Insulin is usually provided by a rapid-acting insulin analogs, such as insulin aspart, insulin lispro, 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.