An overview of insulin

Insulin is a chemical messenger that allows cells to absorb glucose, a sugar, from the blood.

The pancreas is an organ behind the stomach that is the main source of insulin in the body. Clusters of cells in the pancreas called islets produce the hormone and determine the amount based on blood glucose levels in the body.

The higher the level of glucose, the more insulin goes into production to balance sugar levels in the blood.

Insulin also assists in breaking down fats or proteins for energy.

A delicate balance of insulin regulates blood sugar and many processes in the body. If insulin levels are too low or high, excessively high or low blood sugar can start to cause symptoms. If a state of low or high blood sugar continues, serious health problems might start to develop.

Click here to read all about diabetes and how it develops.

In some people, the immune system attacks the islets, and they cease to produce insulin or do not produce enough.

When this occurs, blood glucose stays in the blood and cells cannot absorb them to convert the sugars into energy.

This is the onset of type 1 diabetes, and a person with this version of diabetes will need regular shots of insulin to survive.

In some people, especially those who are overweight, obese, or inactive, insulin is not effective in transporting glucose into the cells and unable to fulfill its actions. The inability of insulin to exert its effect on tissues is called insulin resistance.

Type 2 diabetes will develop when the islets cannot produce enough insulin to overcome insulin resistance.

Since the early 20th century, doctors have been able to isolate insulin and provide it in an injectable form to supplement the hormone for people who cannot produce it themselves or have increased insulin resistance.

Learn about the discovery of insulin here.

A person can take different types of insulin based on how long they need the effects of the supplementary hormone to last.

People categorize these types based on several different factors:

• speed of onset, or how quickly a person taking insulin can expect the effects to start.
• peak, or the speed at which the insulin reaches its greatest impact
• duration, or the time it takes for the insulin to wear off
• concentration, which in the United States is 100 units per milliliter (U100)
• the route of delivery, or whether the insulin requires injection under the skin,into a vein, or into the lungs by inhalation.

People most often deliver insulin into the subcutaneous tissue, or the fatty tissue located near the surface of the skin.

Three main groups of insulin are available.

Fast-acting insulin

The body absorbs this type into the bloodstream from the subcutaneous tissue extremely quickly.

People use fast-acting insulin to correct hyperglycemia, or high blood sugar, as well as control blood sugar spikes after eating.

This type includes:

• Rapid-acting insulin analogs: These take between 5 and 15 minutes to have an effect. However, the size of the dose impacts the duration of the effect. Assuming that rapid-acting insulin analogs last for 4 hours is a safe general rule. Examples: Aspart (Novolog), Lispro (Humalog).
• Regular human insulin: The onset of regular human insulin is between 30 minutes and an hour, and its effects on blood sugar last around 8 hours. A larger dose speeds up the onset but also delay the peak effect of regular human insulin. Examples: Humulin R, Novolin R

Intermediate-acting insulin

This type enters the bloodstream at a slower rate but has a longer-lasting effect. It is most effective at managing blood sugar overnight, as well as between meals.

Options for intermediate-acting insulin include:

• NPH human insulin: This takes between 1 and 2 hours to onset, and reaches its peak within 4 to 6 hours. It can last over 12 hours in some cases. A very small dose will bring forward the peak effect, and a high dose will increase the time NPH takes to reach its peak and the overall duration of its effect. Examples: Humulin N, Novolin N.
• Pre-mixed insulin: This is a mixture of NPH with a fast-acting insulin, and its effects are a combination of the intermediate- and rapid-acting insulins. The mixtures can be in various combinations from 50:50 to 75:25 or 70:30. An example includes Novolog 70/30.

Long-acting insulin

While long-acting insulin is slow to reach the bloodstream and has a relatively low peak, it has a stabilizing “plateau” effect on blood sugar that can last for most of the day. Glargine (Lantus) is an example.

It is useful overnight, between meals, and during fasts.

Long-acting insulin analogs are the only available type, and these have an onset of between 1.5 and 2 hours. While different brands have different durations, they range between 12 and 24 hours in total.

Learn more about diabetes treatment by clicking here.

Insulin is a vital hormone that controls how cells and tissues absorb energy as well as the breakdown of fats and proteins.

Clusters of cells in the pancreas called islets secrete this hormone. When cells in the body respond less to its instructions, insulin resistance is increasing.

In some people, the immune system attacks the islets, halting insulin production and leading to type 1 diabetes. Type 2 diabetes occurs when insulin resistance coexists with a lack of compensatory increase in insulin production.

People can take insulin shots to counteract the effects of insulin resistance. There are fast, intermediate, and long-acting insulins that a person would take depending on how quickly they need to see a drop in blood sugar and the duration for which a person needs to control blood sugar.