Insulin 101: How it works, types, delivery & more

Insulin 101: How it works, types, delivery & more
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For people who have or are at risk of diabetes, understanding what insulin is and how it functions is crucial. This article will talk about insulin, its purpose, and how it is used to manage diabetes.

What is insulin?

Hormones are chemical messengers produced in one part of the body and released to the bloodstream, where they travel to their destination organs or cells. Once there, they help the organs or cells do their job.

Insulin is a hormone. It is secreted by the beta cells of the islet of Langerhans found in the pancreas, an organ just behind the stomach. Essentially, the function of insulin is to allow sugars (glucose) to enter the cells.

You see, our cells cannot function well without sugar because they use it for energy.

Is insulin different from Glucagon?

The pancreas both produces insulin and glucagon: the first by the beta cells, the latter, by the alpha cells.   If insulin functions to lower glucose in the blood, glucagon serves to keep the blood sugar high enough for the body to function well.

When we consume carbohydrates, our glucagon levels fall. This is to prevent hyperglycemia. Now, when we eat a high protein meal, glucagon works by increasing blood glucose.

Insulin production and function

Like what we just mentioned, the hormone insulin helps cells gain energy by allowing the entrance of sugars. To better understand this function of insulin, let’s review the following concepts:

Insulin works like a key

The first concept you need to learn is that insulin acts as a key. On the surface of the cell is a lock called the insulin receptor. To open this lock, insulin must first bind with it.

After the insulin binds with the insulin receptor, the cell’s surface opens and glucose enters and gets picked up by glucose transporters.

The pancreas produces insulin in two ways

Another concept to keep in mind is this: the pancreas releases insulin in two ways: basal and bolus.

Basal insulin is what the pancreas produces round the clock, regardless of whether you eat or not. Basal insulin helps bring down high resting blood sugar. Bolus insulin, on the other hand, is what the pancreas produces immediately after consuming foods.

Insulin also plays a role in protein and fat metabolism

And finally, please remember that while insulin’s primary function is to allow glucose into the cells, it also plays a role in protein and fat metabolism.

Insulin also allows the protein to enter cells and stores extra fat and sugar as fat, which the body can use in the future.

Diabetes and insulin

At this point, let’s talk about the relationship between insulin and diabetes.

Diabetes is a condition where there is too much sugar in the blood (hyperglycemia). People with Type 1 experience hyperglycemia because their pancreas does not produce enough insulin.

Since there’s inadequate insulin to open up the cells, the sugar remains in the blood. Type 2 Diabetes is different. In most cases, people with Type 2 DM produce enough insulin. The problem is they develop what we call “insulin resistance.”

Insulin resistance occurs when the cells poorly respond to insulin. In other words, insulin is present – it’s just that the cells are not sensitive to it (reduced insulin sensitivity). 

Because the cells cannot recognize or respond to the hormone, they won’t open the “gates” to let the sugar in. Increased sugar in the blood then takes place.

Essential facts about insulin resistance

Please keep in mind that not all people who have insulin resistance will develop Type 2 Diabetes. In fact, it’s possible to “reverse” it.

Here are some other facts you should know about insulin resistance:

  • What causes insulin resistance is still unknown. However, factors like family history of Type 2 Diabetes, increased weight, and being inactive serve to increase the risk.
  • If you have insulin resistance, then your goal is to increase your insulin sensitivity.
  • You can become more insulin sensitive by achieving a healthy weight, being physically active, controlling your blood glucose level, managing stress, and getting adequate sleep.
  • Experts say there’s no one test to tell whether you’re insulin resistant or not. Still, some reports say the Insulin Tolerance Test (ITT) is a good method to measure insulin resistance.

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To give your loved one the best care he/she deserves, we provide a free care consultation for you and your loved one, to ensure that they get a Care Professional that best suits their needs.

Types of insulin in diabetes management

It’s a well-known fact that people with Type 1 Diabetes usually manage their condition with insulin therapy. After all, their pancreas cannot produce enough of the hormone. However, please remember that some patients with Type 2 DM also use insulin.

There are five types of insulin used for diabetes management. Looking closely, you’ll notice that they “mimic” the way the pancreas releases the hormone (basal and bolus).

Rapid-Acting Insulin

When it works: Immediately, between 2.5 to 20 minutes

Peak of action: 1 hour after administration

Duration of effect: 2 to 4 hours after administration

Rapid-acting insulin mimics bolus insulin. For this reason, you must eat immediately after you administer it.

In Singapore, Lispro is the commonly available rapid-acting insulin.

Short-Acting Insulin:

When it works: 30 minutes after administration

Peak of action: 2 to 5 hours after administration

Duration of effect: 6 to 8 hours after administration

This type of insulin also mimics bolus insulin. Since it works after half an hour, the patient must administer the insulin 30 minutes before mealtime.

In Singapore, the commonly available short-acting insulin are:

  • Humulin® R
  • Actrapid® HM

Intermediate-Acting Insulin

When it works: 60 to 90 minutes after administration

Peak of action: 4 to 12 hours after administration

Duration of effect: 16 to 24 hours after administration

Intermediate-acting insulin functions like basal insulin.

In Singapore, the commonly available intermediate-acting insulin are:

  • Humulin® N/NPH  human insulin
  • Humulin® L/lente  human insulin
  • Insulatard® HM
  • Monotard® HM

Long-Acting Insulin

When it works: 3 hours after administration

Peak of action: 6 to 14 hours after administration

Duration of effect: Up to 24 hours after administration

This type of insulin is also like basal insulin. One common type of long-acting insulin is called insulin glargine (Lantus®).

In Singapore, the commonly available long-acting insulin is:

  • Humulin® U

Mixed Insulin

Mixed insulin contains either rapid-acting or short-acting insulin plus intermediate-acting insulin. Generally, they start working within 30 minutes to an hour after administration, and their effect lasts for about 16 to 18 hours.

Note that, most patients need a combination of longer-acting and shorter-acting insulin. However, please remember that each person has different needs, so a doctor’s supervision is always necessary.

Insulin delivery options

One cannot receive insulin orally, so patients need to deliver them via pens, pumps, or syringes.

Insulin pens

An insulin pen looks somewhat like the pen one uses to prick their fingers for blood. It has a slot for a disposable needle and an injection button. The pen contains the insulin cartridge and a dose adjustment dial.

Insulin pens can be disposable or reusable. If it’s disposable, then you need to discard it once the cartridge runs out of insulin, when it’s been out of the fridge for a certain period (usually a month), or when it reaches the use-by date.

A reusable insulin pen only requires you to discard the cartridge and insert a new one.

Regardless of the type of pen, never store it with the needle still attached. Air may enter the cartridge, and leakage may occur.

Insulin pumps

An insulin pump is a programmable device the size of a pager. It contains an insulin reservoir and has a cannula or small tube attached to it that goes through the skin.

Because it is programmable, the patient can “instruct” the pump to continuously inject small amounts of insulin. They can also program it to deliver higher doses of insulin each mealtime.

Please note that while the pump can last for years, some parts need replacement every few days or so. Case in point, the cannula attached to the skin needs changing every 2 to 3 days to avoid the onset of infection.

One of the advantages of using an insulin pump is it is convenient. Patients don’t need to stop what they’re doing to prepare the insulin; they simply need to program the dose and administration time. Insulin pumps also reduce the risk of forgetting a dose.

Insulin injection or insulin jab

Perhaps, the most common way to deliver insulin is through an insulin injection or jab. Because an insulin injection is a manual method, you either need help or learn how to do it yourself.

The most common sites for insulin injection are the abdomen, arms, thighs, and buttocks. It is important to rotate injection sites regularly.

Choosing insulin syringes

Insulin syringes come in a lot of forms and sizes.

The general rule in choosing an insulin syringe is to pick the smallest one that can hold the largest dose you administer at a time.  The smaller the syringe is, the easier it is for you to read its calibrations or markings. This then helps you draw an accurate insulin dose.

Now, if the largest dose comes close to the syringe’s maximum capacity, choose the next size up. That way, you can still make adjustments when necessary.

Needle lengths are usually 6mm, 8mm, 10mm, and 12.7mm. In most cases, it is preferable to use 6mm and 8mm syringes; however, since needle length may affect insulin absorption, consult your doctor first.

The same thing is true for needle thickness or gauge (G). Please note that the higher the gauge is, the thinner the needle. For instance, 31G is thinner than 28G. Remember that thinner needles are not always preferable as the possibility of bending is there.

To choose the best insulin syringe for you, the best course of action is to talk to your doctor.

Here are the other crucial things to remember when using an insulin syringe:

  • Maintain the integrity of the syringe. Always keep its outer surface clean and dry.
  • Be mindful of the needle. Discard the syringe if the needle appears bent or dull, or if it came in contact with surfaces other than your skin.
  • Never reuse needles even if they appear okay. Reusing needles increases the risk of infection. Furthermore, new needles lead to less painful injections.
  • Before insulin injections, inspect the site. Make sure that it has no redness or other signs of infection.
  • Never share syringes.

Inhaled insulin

You may or may not have heard of it yet, but insulin can also be delivered through inhalation. The medicine comes in aerosol powder, with the brand name Afrezza®. However, due to its unconventional nature, Afrezza® sparked controversy.

On their website, it was mentioned that Afrezza® can result in serious side effects like bronchospasms. Additionally, people who have long-term lung problems, such as chronic obstructive pulmonary disease, should steer clear of this medicine.

If you’re interested in inhaled insulin, discuss it first with your physician.

Insulin side-effects

Insulin side effects depend on several factors like the type, brand, and patient tolerance to the drug. In general, insulin therapy can lead to the following side effects:

  • Discomfort on the injection site, like the appearance of redness, swelling, and lumps.
  • Initial weight gain, since the cells will start using glucose again.
  • Coughing, for those who take inhaled insulin.
  • Hypoglycemia or low blood sugar levels (most common).

Hypoglycemia as a side-effect from insulin therapy

Low blood sugar usually happens when patients use insulin because the cells start taking up glucose from the blood. It can lead to the following symptoms:

  • Sweating
  • Paleness
  • Dizziness
  • Fatigue
  • Confusion
  • Trouble speaking
  • Loss of consciousness


In case you experience hypoglycemia, it’s best to follow the plan you and your doctor discussed. In most cases, the following emergency treatment works:

  • If you feel any of the symptoms of hypoglycemia, check your blood sugar immediately.
  • If the measurement is lower than 4mmol/L, eat or drink ONE of the following:
    • ½ glass of juice
    • 3 teaspoons of honey, sugar, or syrup.
    • 3 sweets, like candies: choose those that are not sugar-free. As much as possible, don’t choose sweets with fat content like chocolate or cake as they don’t raise blood sugar as quickly.
    • ½ can of soft drink: don’t drink the diet or zero sugar variety.
  • Wait 15 minutes and recheck your blood sugar.
  • Repeat the first two steps until your blood sugar reaches 4 to 6 mmol/L.
  • Once your blood glucose is higher than four mmol/L, consume ONE of the following:
    • Your planned meal or snack if it’s scheduled within half an hour.
    • Biscuits with cheese or peanut butter OR half a sandwich if your next meal is more than an hour away.
  • Finally, please take note of the incident and report it to your doctor.


Your risk of experiencing hypoglycemia due to insulin therapy decreases when you:

  • Administer insulin and take your other medicines as prescribed.
  • Follow your mealtime schedule.
  • Consume extra foods before working out or doing heavy physical activity.
  • Eat a snack or drink some juice or milk if it’s impossible to eat your meal.
  • Carry extra sweets everywhere you go.

How to store insulin

The first rule for storage is to know how the insulin normally looks like. For instance, most insulin medicines are clear, but some types are uniformly cloudy once you gently roll the pen or vial.

Never use insulin that appears different from how it normally looks like. This tip helps you distinguish between good quality insulin and those that are not safe for use.

For storage, follow these best practices:

  • Keep all unopened insulin inside the fridge – not the freezer. In case you accidentally freeze your insulin, discard them right away. Please do not use them even after they thaw.
  • Don’t forget to write down the date when you open a vial or pen.
  • Opened pens or vials should be kept at room temperature.
  • Dispose of vials or pens 28 days after opening them.
  • In some cases, you should also discard the pen if there are less than 12 units of insulin in the cartridge.

Other ways to control blood glucose levels

Alongside insulin therapy, please remember that maintaining a healthy weight, eating a healthy diet , and staying physically active is also essential in controlling your blood sugar levels.

For this reason, be in constant contact with your physician. They can help you make healthy meal plans, devise an appropriate exercise routine, and track your progress in blood glucose control.

This article was first published in Homage.

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