Everything You Need to Know About Insulin

Written by Valencia Higuera | Published on September 3, 2014
Medically Reviewed by Kenneth R. Hirsch, MD on September 3, 2014

Everything You Need to Know About Insulin

Insulin is a hormone made in the pancreas, a gland located behind the stomach. It allows the body to use glucose for energy. Glucose is a type of sugar found in many carbohydrates. After a meal or snack, the digestive tract breaks down and changes carbohydrates into glucose. Once glucose releases into the bloodstream, insulin causes cells throughout the body to absorb this sugar and use it for energy.

Insulin also plays a key role in balancing blood glucose levels. When there’s too much glucose in the bloodstream, insulin signals the body to store excess sugar in the liver. This sugar isn’t released until your blood sugar drops, such as in-between meals or at times of stress when your body needs an extra boost of energy.

How Insulin Affects Diabetes?

Diabetes occurs when your body doesn't use insulin properly, or doesn't produce enough insulin. There are two main types of diabetes: type 1 and type 2.

Type 1 diabetes is a type of autoimmune disease where the body no longer produces insulin. In this disease, failure to produce insulin is due to the immune system having destroyed all of the insulin-producing cells in the pancreas.  This disease is more common in young people, although it can develop in adults. Type 2 diabetes also affects people of any age, but typically develops later in life. 

Unlike type 1 diabetes, the primary problem in persons with type 2 is a decreased response to the effects of insulin by the glucose requiring cells of the body (insulin resistance).  Therefore, throughout much of the course of type 2 diabetes, patients may actually overproduce insulin in an effort to keep blood sugar levels normal.  However, over many years, this overproduction can cause the insulin-producing cells in the pancreas to burn out.  At that point, such patients become dependent upon insulin treatment.

Insulin injections can treat both types of diabetes. But many people with type 2 diabetes can manage their blood sugar with lifestyle changes and medication. Sometimes, patients with type 2 diabetes are unable to achieve normal blood sugar levels using only oral medications and lifestyle modification, and these people may need insulin to maintain a healthy blood sugar level. Because people with type 1 diabetes cannot make insulin, they must use insulin to control the disease.

Types of Insulin

Insulin cannot be taken by mouth. It must be injected with a syringe, an insulin pen, or an insulin pump. Although at the cellular level all insulin’s have the same effect, chemical modification of the insulin protein has allowed for the development of different types of insulin for the treatment of diabetes.  The main important differences between the various types of insulin used in diabetes treatment are the speed of onset and the duration of the effects of the drug.

Rapid-Acting Insulin

This type of insulin begins working approximately 15 minutes after an injection. The injection can last for 3 to 5 hours, and it's often taken before a meal.

Short-Acting Insulin

Taken before a meal, insulin starts working in about 30 minutes to 60 minutes after an injection, and lasts 5 to 8 hours.

Long-Acting Insulin

Insulin may not start working until one hour after an injection, but it can lasts up to 26 hours.

Intermediate-Acting Insulin

This type of insulin starts working in 1 to 3 hours after injection, and may last 12 to 16 hours.

Injecting Insulin

Insulin is injected under the skin, and your doctor or a nurse can provide instructions on how to administer injections. You can inject insulin in many different parts of your body, such as the thigh and abdomen. Don’t inject insulin within two inches of the belly button. You should vary the location of injections to prevent skin thickening.

Diabetes treatment varies by person. Your doctor may instruct you to take insulin 60 minutes before a meal, or just before eating. The amount of insulin you'll need on a daily basis depends on numerous factors including your diet, your level of physical activity, and the severity of your diabetes. Some people only need one insulin shot a day, while others need three or four shots a day. Your doctor may also combine a rapid-acting insulin with a long-acting insulin.

Insulin Reactions

Insulin reactions (hypoglycemia) can occur in people who take insulin to manage their diabetes. When you take insulin, it needs to be balanced with food or calories. If you exercise too much or don't eat enough, the level of sugar in your blood can drop too low and trigger a reaction. Signs of an insulin reaction include:

  • tiredness
  • frequent yawning
  • unable to speak
  • sweating
  • confusion
  • loss of consciousness
  • seizures
  • muscle twitching
  • pale skin

To stop the effects of an insulin reaction, carry at least 15 g of a fast-acting carbohydrate with you at all times (American Academy of Family Physicians). For example:

  • about a 1/2 cup of non-diet soda
  • 1/2 cup of fruit juice
  • five lifesaver candies
  • 2 tablespoons of raisins


Insulin can keep your blood sugar level within a healthy range and reduce the risk of diabetes complications, such as blindness and limb amputation. It's important that you monitor your blood sugar regularly, and make lifestyle changes to prevent your blood sugar level from getting too high.

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Show Sources

  • American Diabetes Association. Standards of medical care in diabetes--2011. Diabetes Care. 2011;34 Supl 1:S11-S61.
  • Cryer PE. Glucose homeostasis and hypoglycemia. In: Kronenberg HM, Melmed S, Polonsky KS, Larsen PR. Kronenberg: Williams Textbook of Endocrinology. 11th ed. Philadelphia, Pa: Saunders Elsevier; 2008:chap 33. http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001423/
  • American Diabetes Association. Standards of medical care in diabetes--2010. Diabetes Care. 2010 Jan;33 Suppl 1:S11-61.
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