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Insulin Basics

Nina Ghamrawi, MS, RD, CDE
July 2, 2023
May 31, 2024

Insulin is a natural hormone that is basic and necessary to live. When our bodies can no longer make enough, we need it in the form of injections in order for our cells to absorb energy from food.

There are different types of insulin depending on how quickly they work, when they peak, and how long they last.

All insulin available in the United States is manufactured in a laboratory, but animal insulin can still be imported for personal use.Inside the pancreas there are beta cells make the hormone insulin. When you eat a meal, naturally beta cells release insulin to help the body use or store the blood glucose it gets from food. It does this by acting like a key to open the doors in your cells that typically absorb insulin, and help those cells pull insulin out of the blood and into the organs that need it-  like the brain, muscles, and heart, to name a few.In people with Type 1 Diabetes, the beta cells in the pancreas have been destroyed and the pancreas can now no longer make insulin. For people with Type 1 Diabetes, or people with Type 2 who also have reduced beta cell insulin production, they must receive insulin injections (think of it as a supplement) in order for their organs to absorb the energy from food.

People with Type 2 Diabetes generally make insulin, but their bodies don't respond well to it. Some people with Type 2 need diabetes pills, insulin shots, or both to help their bodies use glucose for energy.

Insulin cannot be taken as a pill because it would be broken down during digestion just like the protein in food. It must be injected into the fat under your skin for it to get into your blood. In some rare cases insulin can lead to a mild allergic reaction at the injection site. Talk to your doctor if you believe you may be experiencing a reaction.

Characteristics of Insulin

Insulin has 3 main characteristics:

  • Onset is the length of time before insulin reaches the bloodstream and begins lowering blood glucose.
  • Peak time is the time during which insulin is at maximum strength in terms of lowering blood glucose.
  • Duration is how long insulin continues to lower blood glucose.

Types of Insulin

  • Rapid-acting insulin, begins to work about 15 minutes after injection, peaks in about 1 hour, and continues to work for 4 to 6 hours. Types: Insulin glulisine (Apidra), insulin lispro (Humalog), and insulin aspart (NovoLog)
  • Regular or Short-acting insulin begins to work within 30 minutes after injection, peaks anywhere from 2 to 3 hours after injection, and is effective for approximately 3 to 8 hours. Types: Humulin R, Novolin R
  • Intermediate-acting insulin starts to take effect 2 to 4 hours after injection, peaks 4 to 12 hours later, and is effective for about 12 to 20 hours. Types: NPH (Humulin N, Novolin N)
  • Long-acting insulin reaches the bloodstream several hours after injection and continues to work at a fairy consistent level for around 24-hours. Types: Insulin detemir (Levemir) and insulin glargine (Lantus)

Premixed insulin can be helpful for people who have trouble drawing up insulin out of two bottles and reading the correct directions and dosages. It is also useful for those who have poor eyesight or dexterity and is convenient for people whose diabetes has been stabilized on this combination.In 2015 an inhaled insulin product, Afrezza, became available in the U.S. Afrezza is a rapid-acting inhaled insulin that is administered at the beginning of each meal and can be used by adults with type 1 or type 2 diabetes. Afrezza is not a substitute for long-acting insulin. Afrezza must be used in combination with injectable long-acting insulin in patients with type 1 diabetes and in type 2 patients who use long-acting insulin.

  • Inhaled insulin begins working within 12 to 15 minutes, peaks by 30 minutes, and is out of your system in 180 minutes. Types: Technosphere insulin-inhalation system (Afrezza)

Insulin Strength

All insulins come dissolved or suspended in liquids. The standard and most commonly used strength in the United States today is U-100, which means it has 100 units of insulin per milliliter of fluid, though U-500 (5 times more concentrated) insulin is available for patients who are extremely insulin resistant.U-40, which has 40 units of insulin per milliliter of fluid, has generally been phased out around the world, but it is possible that it could still be found in some places (and U-40 insulin is still used in veterinary care).If you're traveling outside of the U.S., be certain to match your insulin strength with the correct size syringe.

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