Insulin Basics: An Expert's Guide

From rapid-acting to long acting and everything in between, an expert explains the insulin options available today to help you manage your diabetes.

Amy's dalmation Bart with diabetes suppliesThe author's dog, Bart, with some diabetes management supplies.

What is insulin and what does it do in the body?

Insulin is a hormone made by the pancreas that allows our bodies to use sugar from carbohydrates in the food that we eat to use as energy in our brains, muscles and nerves or to store it for future use. Insulin helps keeps your blood sugar level from getting too high or too low.

If you have more sugar in your body than it needs, insulin helps store the sugar in your liver and releases it when your blood sugar level is low or if you need more, such as in between meals or during physical activity. Therefore, insulin helps balance out blood sugar levels and keeps them in a normal range. As blood sugar levels rise, the pancreas secretes more insulin.

What is a normal insulin level?

People get blood tests for a variety of reasons, but very few may be asked to have an insulin level drawn and usually completed  to figure out why someone who is not taking insulin has very low blood sugar levels.

If they do, each laboratory that draws blood will give the result and a reference range that is considered a usual level. 

Is insulin harmful to the body?

Insulin is hormone that we usually make in our bodies to help us use the fuel we get from food, so it is safe and natural.  The one thing about insulin, though, is that it can increase someone’s risk for hypoglycemia (low blood sugar) if they take too much.  That is why it is important to work with your healthcare provider to find the right doses of insulin FOR YOU.

What is insulin resistance?

Insulin resistance is when cells in your muscles, fat, and liver cannot respond well to insulin and have a hard time using the sugar that is released in your blood.  The pancreas then makes more insulin to help that sugar enter your cells. As long as your pancreas can make enough insulin to make up for the lower response, your blood glucose levels will stay in the healthy range.  If your body does not produce enough insulin, then the blood sugars rise and medications may be needed. 

What happens when you take insulin?

The most commonly used insulin comes in liquid form which means it must be injected under the skin in order for it to be absored and used.

Depending on the type that is given and WHERE it is injected will determine what actually happens.  As you see from the chart (below) we can get a good idea of WHEN the insulin will START to work (ONSET), when it will work its strongest (PEAK) and when it is finished working (DURATION). We typically can determine if the dose is working correctly for someone by reviewing blood sugar results during the peak times for the insulin taken.

There is an inhaled version that is only very fast acting.  That also follows the same rules as injected insulin and we can determine when it will affect blood sugar levels the most using the onset, peak and duration guidelines below.

What types of insulin are available?

Various types of insulin are used to treat diabetes and include:

  • Rapid-acting insulin: It starts working approximately 15 minutes after injection and peaks at approximately 1 hour but continues to work for two to four hours. This is usually taken before a meal and in addition to a long-acting insulin.
  • Short-acting insulin: It starts working approximately 30 minutes after injection and peaks at approximately 2 to 3 hours but will continue to work for three to six hours. It is usually given before a meal and in addition to a long-acting insulin.
  • Intermediate-acting insulin: It starts working approximately 2 to 4 hours after injection and peaks approximately 4 to 12 hours later and continues to work for 12-18 hours. It is usually taken twice a day and in addition to a rapid- or short-acting insulin.
  • Long-acting insulin: It starts working after several hours after injection and works for approximately 24 hours. If necessary, it is often used in combination with rapid- or short-acting insulin.
  • Insulin can be given by a syringe, injection pen, or an insulin pump that delivers a continuous flow of insulin.

Below is a chart of the current types of insulin available with specific information about how it is delivered, when it expires after opening, onset, peak and duration:

Types of Insulin Chart

Your doctor will work with you to figure out which type of insulin is best for you depending on whether you have type 1 or type 2 diabetes, your blood sugar levels,and your lifestyle.

People with type 1 diabetes cannot make insulin because they no longer can make enough of it. They will need insulin to live.

People with type 2 diabetes do not respond well or are resistant to insulin. They may need insulin to help them better process sugar. Depending on blood sugar levels, people with type 2 diabetes may first be treated with oral medications, along with meal planning changes and being more physically active. 

It is important to remember that the longer that someone has type 2 diabetes, the more help their pancreas will need, meaning they will eventually need insulin. This does not mean that someone did not take care of their diabetes correctly. Insulin is one of the BEST diabetes medications to help reduce blood sugars and A1C, which will help to reduce long-term complications.


Updated on: March 8, 2019
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