Medically reviewed on May 28, 2018
What is Insulin?
Insulin is a hormone that is produced naturally in our bodies. Its main role is to allow cells throughout the body to uptake glucose (sugar) and convert it into a form that can be used by these cells for energy. Without insulin, we cannot survive, and death from diabetes was a common occurrence until insulin was discovered in the early 1900s by Frederick Banting and Charles Best.
Naturally occurring human insulin is made by beta cells within the pancreas. When people without diabetes eat food, these beta cells sense sugar or other carbohydrates in the blood and release just the right amount of insulin necessary to maintain normal blood sugar levels.
What is insulin used for?
Insulin is used in the treatment of people with type 1 diabetes who produce little or no insulin. It may also be used in the treatment of type 2 diabetes if insulin levels remain low despite the use of other types of medications, although most people with type 2 diabetes do not require insulin in the early stages of the disease.
Insulin may also be given to pregnant women who develop a type of diabetes during pregnancy called gestational diabetes.
What are the differences between insulins?
Insulin is available as synthetic human insulin (made in a laboratory but resembles naturally occurring human insulin) and insulin analogues (human insulin that has been genetically modified). Insulin analogues are better than standard human insulin at mimicking natural insulin release. They have a more predictable duration of action and more reliable absorption.
Insulins are typically classified as fast-acting (includes rapid-acting and short-acting insulins), intermediate-acting, and long-acting insulins.
Common Insulins available in the U.S.
Ultra long-acting insulin
- insulin degludec: Tresiba
How is insulin administered?
Insulin is most commonly administered subcutaneously (under the skin) and there are three main delivery methods:
- Insulin Pens: these hold a replaceable cartridge of insulin and use a replaceable needle to puncture the skin and deliver the insulin subcutaneously
- Insulin pumps: these are small computerized devices that deliver a continuous supply of insulin under the skin. They are also known as continuous subcutaneous insulin infusion devices (CSII)
- Via a syringe and needle using a vial of insulin.
So far, nobody has successfully made an oral insulin tablet that delivers an effective dose of insulin. The problem is that insulin degrades in the stomach and intestine before it even has a chance to get absorbed into the blood stream. In hospital, insulin may be administered directly into a vein or into a muscle under certain circumstances.
What are the side effects of insulin?
Symptoms include a headache, sweating, trembling, anxiety, confusion, irritability, rapid breathing, or a fast heartbeat. People with hypoglycemia may also faint and severe hypoglycemia that is left untreated may be fatal.
Hypoglycemia is relatively common because insulin requirements can vary depending on the food you eat, exercise you do, and how well you are. Hyperglycemia (high blood sugar levels) from too low an insulin dose can also occasionally occur.
Other common side effects include:
- swelling, itching, redness or lumps around the injection site
- weight gain
- electrolyte disturbances (including low potassium and low magnesium levels)
- blurred vision (usually temporary).
Insulin analogues are less likely to cause weight gain or low night-time blood sugar levels than standard human insulins.
How long does insulin last for?
Insulin is easily broken down by extreme temperatures, which means you need to be careful if you live in a part of the U.S. that gets very hot in summer, or very cold in winter.
Opened and in-use cartridges and vials are fine to keep at room temperature (59 to 77 degrees Fahrenheit [15-25 degrees Celcius]) for up to 28 days. The exception is Tresiba which, once in use, is stable for up to 8 weeks at room temperature. If you are going out in the sun, always use an insulated bag protected by a cool pack to ensure your insulin doesn't heat up; but avoid freezing it. During cold weather, keep your insulin supplies close to your skin so your body heat keeps them at a more even temperature.
All unopened vials and cartridges should be kept in the fridge, between 36-46 degrees Fahrenheit (2-8 degrees Celcius). Discard any insulin that you think may have inadvertently got too hot or too cold. The expiry date on insulin applies to unopened, refrigerated insulin.
What else should I know about insulin?
Our insulin requirements vary depending on the food we eat, how much activity we do, our general and mental health, how much we currently weigh, and our age.
Talk to your doctor about how you should adjust your insulin dose when you:
- Are prescribed other medications (such as prednisone) that may affect your body's sensitivity to insulin
- Are unwell or have an infection
- Feel stressed or exceptionally tired
- Gain or lose weight
- Reduce or increase your activity levels
- Are trying for a baby or find out you are pregnant.
You should also regularly monitor your blood glucose levels and be able to count your calories (particularly carbohydrates) and know how to calculate how much insulin to take and when to adjust it. If you don't know how to do this, ask your doctor or talk to a diabetes nurse.
You should know what to do if your blood sugar level goes too high or too low and have an action plan in place so that your family and friends also know what to do.
Most insulin in the U.S. is sold as a concentration of 100 units per ml (U100). However, there are currently four concentrated products on the market:
- Humulin R (human insulin) which has a 500 units per ml (U500) strength available
- Humalog (insulin lispro) which has a 200 units per ml (U200) strength available
- Toujeo Solostar which contains 300 units per ml (U300) of insulin glargine
- Tresiba (insulin degludec) which has a 200 units per ml (U200) strength available.
- 1 in 3 With Type 1 Diabetes Produce Insulin: Study. Web MD. http://www.webmd.com/diabetes/news/20141229/1-in-3-people-with-type-1-diabetes-still-produce-insulin-study-says#2
- Cantley J, Ashcroft FM. Q&A: insulin secretion and type 2 diabetes: why do β-cells fail? BMC Biology. 2015;13:33. doi:10.1186/s12915-015-0140-6
- Leontis L, Hess-Fischl. Type 2 Diabetes. Causes, Genetics and Lifestyle Choices Play a Role. Endocrine Web. https://www.endocrineweb.com/conditions/type-2-diabetes/type-2-diabetes-causes
- Liamis G, Liberopoulos E, Barkas F, Elisaf M. Diabetes mellitus and electrolyte disorders. World Journal of Clinical Cases : WJCC. 2014;2(10):488-496. doi:10.12998/wjcc.v2.i10.488.
- MacGill M. Discovery of Insulin. Medical News Today 2016. http://www.medicalnewstoday.com/info/diabetes/discoveryofinsulin.php
- Martin JH, Russell A, O’Moore-Sullivan T, Prins JB (2011) Insulin Analogues: Reviewing the Pros and Cons in Managing Diabetes Mellitus. J Pharmacogenomics Pharmacoproteomics 2:106. doi: 10.4172/2153-0645.1000106
- Quianzon CC, Cheikh I. History of insulin. Journal of Community Hospital Internal Medicine Perspectives. 2012;2(2):10.3402/jchimp.v2i2.18701. doi:10.3402/jchimp.v2i2.18701.
- Type 1 diabetes. Mayo Clinic. http://www.mayoclinic.org/diseases-conditions/type-1-diabetes/diagnosis-treatment/treatment/txc-20340999
- Type 2 diabetes Medline Plus. US National Library of Medicine. https://medlineplus.gov/ency/article/000313.htm
- Types of Insulin. Diabetes Education Online. UCSF Medical Center. https://dtc.ucsf.edu/types-of-diabetes/type2/treatment-of-type-2-diabetes/medications-and-therapies/type-2-insulin-rx/types-of-insulin/
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