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All About Insulin

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All About Insulin

By Nina Nazor

What is Insulin?

Insulin is a hormone secreted by your pancreas and its function is to regulate blood glucose levels. Insulin works like a key to open the door of the cells so glucose – the fuel you get from food - can come inside and be converted into energy.

Think of a corridor full of doors. You need a key to unlock each door so you can put glucose in each room. Well, insulin is that key and if it is not produced in the right amounts or if it cannot open the doors because it is cracked, then glucose builds up in the blood causing your blood sugar to go up. This is called hyperglycemia (high levels of blood glucose) and is the common manifestation of diabetes.

Insulin production

Normal insulin production in the pancreas is released in two different ways, basal and meal-stimulated. Lets see what it means.

Basal insulin secretion, means that a constant amount of insulin is released by the pancreas, usually between 0.5 to 1.0 units per hour. This helps your body get the fuel needed for different activities you perform every day. Basal insulin is a constant production of very small amounts of insulin.

Pulsatile insulin secretion (usually 1 unit of insulin per 10 g of carbohydrates) is released after a meal and helps you body metabolize the food you eat. This allows glucose and other nutrients to reach the cells to be used to produce energy or to be stored as fat. Every time blood glucose concentrations are over 100 mg per dL, insulin is released.

Normal insulin metabolism in people without diabetes works by balancing glucose levels every time a meal is eaten, or whenever the liver or muscles release glucose to the bloodstream. Insulin production usually reaches the highest levels one hour after having a meal, which makes blood glucose concentrations get back to normal within 2 hours. This does not happen in people with diabetes.

Diabetes treatment consists of imitating this normal balance of insulin and glucose in order to keep blood glucose levels as near as normal as possible. That's why the most common regimens of insulin mix short acting and intermediate or long acting insulin, trying to mimic normal insulin production to have you covered through the day and at the highest glucose peaks after eating a meal.

In case you have type 2 diabetes and you take pills, the treatment prescribed by the doctor will also try to imitate insulin production with one pill, a combination of them, or a combination of insulin and pills. So, no matter what medication you take, you must understand how they work and learn to think like your pancreas.

Types of Insulin

Peaks and duration of insulin action by insulin type

Rapid Acting Insulin
Humalog® (Lilly) and Novolog® (Novo Nordisk) are the fastest acting types of insulin. Their are ideal for using before a meal and for counting carbs so you can cover your meals or snacks. Novolog® has been approved by the FDA for use in insulin pumps.

Regular Insulin
Novo Nordisk and Lilly also make short-acting insulin, or Regular Insulin. This type of insulin takes thirty minutes to two hours to start acting and continues to cover you for four to six hours.

Intermediate Acting Insulin
Intermediate action insulin, also manufactured by Lilly and Novo Nordisk with the brand names of Humulin® and Novolin®, or the generic NPH and Lente, takes longer to start its action, has a longer peak, and cover you longer than Regular, Novolog® or Humalog®. NPH and Lente are recommended for long-range coverage.

Long Acting Insulin
Lantus® (by Aventis) and Humulin UltraLente® (by Lilly) are designed to be used imitating basal insulin production, that means that they can provide coverage a small and continuous insulin need rather than the peaks needed when a meal is digested.

The times of action are just general guidelines. Your body may react differently depending on the injection site, the time of day, changes in your weight, and the exercise you do.
Some types of insulin are pre-mixed to decrease the number of injections necessary and others have to be injected individually. Your doctor or diabetes educator will tell you what types are the best for you and whether you can mix them or not.

A note of caution, always make sure you consult with your Diabetes Care Team before making any changes to your regimen.

Peaks and duration of insulin action by insulin type

The following chart explains the times of action of the different types of insulin.

Humalog® and Humulin® are registered trademarks of Eli Lilly.
Novolin®, Novolog® y Velosulin® are registered trademarks of Novo Nordisk.
Lantus® is a registered trademark of Aventis.





Rapid Acting


Humalog® (Lispro)

< 15 min

30-90 min

< 5 hours

Novolog® (Aspart)

10-20 min

1-3 hrs

3-5 hrs



Humulin® R

30-60 min

2-3 hrs

4-6 hrs

Novolin® R

30 min

2.5-5 hrs

8 hrs

Velosulin® BR

30 min

1-3 hrs

8 hrs



Humulin® N

2-4 hrs

4-10 hrs

14-18 hrs

Novolin® N

90 min

4-12 hrs

24 hrs

Lente® (L)


Humulin® L

3-4 hrs

4-12 hrs

16-20 hrs

Novolin® L

2.5 hrs

7-15 hrs

22 hrs



Humulin® U

6-10 hrs


20-30 hrs



Humalog® 75/25

15 min

1-6.5 hrs

18-26 hrs

Humulin® 70/30

15-30 min

2-12 hrs

18-24 hrs

Novolin® 70/30

30 min

2-12 hrs

24 hrs

Humulin® 50/50

15-30 min

2-12 hrs

18-24 hrs

Peakless/Basal Action
Lantus®* (insulin glargine)

1-1½ hour

No peak time

20-24 hours

Inhaled Insulin

10 minutes

90 minutes

6 hours


Rotation of the Injection Sites: Changing the spot where you give your insulin shots.

It is important to change the spot where you give your insulin injection every day. Rotating the injection sites you use to help avoid damage to your tissues which would affect insulin absorption.
When you use an area over and over to inject your insulin, the tissue of that area forms scars and lumps. You must try to prevent them by changing the sites of injection.

Leave at least one inch from the exact site of injection, and try to use different areas of your body for each shot throughout the day.

You must also know how different areas of your body absorb insulin at a different speed. Insulin could be absorbed faster or slower depending on the site you use for a shot.

Also, if you exercise the site you chose for a shot you can increase the speed of absorption of insulin. For example, if you give yourself a shot in your legs and then you get out to walk, you may end up speeding the absorption of insulin and that can cause you a low.

Remember that if you have any questions about insulin, you must talk with a member of your Diabetes Care Team, they are the experts helping you control diabetes.