All About Insulin

Insulin is a hormone, which is a type of chemical. In the body, insulin is produced in the pancreas. It is needed to allow sugars (glucose) from food to enter cells. There, it is broken down (metabolized) to produce the energy needed for the cells to work properly.

How is insulin made?

At first, pancreases from cows and pigs were used produce insulin. Pork insulin is still on the market. However, since 1983 human insulin has been available. It is called biosynthetic human insulin. This is produced in a laboratory by introducing a synthetic (man-made) human gene into bacteria or yeast. This produces insulin that is exactly the same as that created in the human pancreas. Through further changes, people can now prepare different insulins (called insulin analogs) with different action times. Although some people still use pork insulin, most now receive human insulin products and insulin analogs.

Insulin Action Times

How does insulin act in the body?

Biosynthetic human insulin is generally divided into four groups:

• fast-acting
• short-acting (also referred to as rapid-acting)
• intermediate-acting
• long-acting 

Insulins are also described according to their course of action:

• onset is the time it takes for the insulin to start working

• peak describes the period when the insulin is working at its strongest
• duration describes the length of time before the effect of the dose wears off

Insulin’s effect: how soon, how long

Type of insulin	Appearance	Onset	Peak	Duration
Fast-acting (Lispro/Humalog, Aspart/NovoRapid)	Clear	5 to 10 min.	First 2 hours	3 to 4 hours
Short-acting (Regular)	Clear	½ to 1 hour	2 to 4 hours	4 to 6 hours
Intermediate-acting (NPH or Lente)	Cloudy	2 to 4 hours	6 to 12 hours	18 to 24 hours
Slow or long-acting (Ultralente) Glargine	Cloudy	4 hours	Minimal peak	20 to 30 hours
These times represent averages for each preparation. They may vary from person to person, from one injection site to another, and to some extent in the same person from day to day. Lente insulin may have a slightly longer duration of action than NPH.

Insulin strength and packaging

In North America insulin is produced at a concentration of 100 units/1 mL. It is available in two ways:

• bottles to be used with needles (syringes). Each bottle of insulin holds 10 mL, or 1,000 units. 
• cartridges used with insulin pen injectors or continuous pumps. Pen cartridges are usually 3 mL (300 units).