A Beginners Guide to Basal and Bolus Insulin

Insulin is the hormone that allows glucose in the blood to enter cells and provide them with energy to function. Without it, the glucose stays in the bloodstream, causing chronic high blood sugar levels and severe diabetes-related health complications. 

Insulin therapy is the only treatment for people with type 1 diabetes and sometimes a necessary option for those with type 2 diabetes.

But taking insulin isn’t as simple as taking tablets. First, it's a liquid medication that needs to be injected subcutaneously, sometimes several times a day. Second, it requires precise dosage and thorough blood glucose monitoring. Third, it’s a very unstable medicine that must be manipulated and stored with caution. And fourth, there are more than 20 different types of insulin! 

The two main types of insulin are basal and bolus. While the basal one acts as a slow background insulin, injecting bolus insulin helps control after-meal blood sugar.

Diabetic patients are often prescribed both basal and bolus insulin. Understanding the difference between the two and how they work together is essential for good diabetes management.

Related article: Does insulin need to be refrigerated? How to store it properly?

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What is basal insulin?

Basal insulin, also called background insulin or long-acting insulin, is a slow-acting type of insulin used to keep blood glucose levels within range during periods of fasting, such as in-between meals or overnight

The body, more precisely the liver, is constantly secreting glucose to send it to the bloodstream and feed the cells with energy. This process, called the glycogenolysis, is essential for our body to function.

When you don't have diabetes, your pancreas naturally releases background insulin to send the liver-produced glucose from the bloodstream to the cells. However, when you have insulin-dependent diabetes, your pancreas does not produce enough of this background insulin (or not at all). That causes blood sugar to rise at an alarming rate, even when you're not eating any carbohydrates or sugar.

Basal insulin mimics the natural background insulin. It slowly acts and releases micro-doses of pure crystalline insulin into our bloodstream throughout the day and night (generally for 12 to 24 hours, depending on the type of insulin). It’s usually injected once or twice daily.

Such long-acting insulins play a major role in type 1 diabetes management and are sometimes necessary for people with type 2 diabetes too.

There are three main types of basal insulin with different onset times (how quickly they start working), durations (how long their effects last), and peak times (when the effects peak).  

Intermediate-acting insulin (basal) 

Intermediate-acting insulin is the most prescribed basal insulin in the U.S. It reaches the bloodstream around one to four hours after the injection, peaks four to 12 hours later, and keeps working for about 12 to 18 hours.

It’s administered once or twice daily and can sometimes be mixed with bolus insulin (fast-acting insulin).

Related article: How to mix two insulins in one syringe?

Intermediate-acting insulin is also referred to as NPH insulin (Neutral Protamine Hagedorn insulin) or isophane insulin. It's sold under the brand names Humulin-N, Novolin-N, and ReliOn, and is available in injectable pens, vials, and cartridges for insulin pumps.

Unlike most other types of insulin, NPH basal insulin looks cloudy instead of clear.

Related article: Clear vs. cloudy insulins

Long-acting insulin (basal)

Long-acting insulin remains in your bloodstream longer than intermediate-acting one. There are two types of long-acting basal insulin on the U.S. market, including detemir (sold under the name Levemir) and glargine (sold under the names Lantus, Toujeo, and Basaglar).

Unlike intermediate-acting NPH insulin, long-acting ones do not have any peak time of action. Instead, they work steadily throughout the day, with an onset time at 1 to 4 hours after the injection, with a duration of up to 24 hours.

These insulins look clear. They're usually administered once daily and can't be mixed with other insulin.

Related article: What happens if you miss a dose of insulin?

Ultra-long-acting insulin (basal)

Ultra-long-acting insulins are relatively new products. They stay in the bloodstream for 36 to 42 hoursand do not have any peak time.

Degludec basal insulin (marketed as Tresiba) was released in 2016 and can stay in the bloodstream for up to 42 hours. It’s available in two strengths (100 U/mL and 200 U/mL). Toujeo U-300 is also considered ultra-long-acting insulin by some, while others classify it in the long-acting category.

Related article: How to convert insulin units to mL?

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What basal insulin is good for you?

Choosing one type of basal insulin eventually depends on your lifestyle and diabetes management. There are many factors to consider, including your weight, diet, average HbA1c, how much insulin your pancreas still produces, how comfortable you are with injections, and more.

The type of basal insulin that’s best for you is really something that can only be discussed with your diabetes medical team. Never use an insulin that you have not been prescribed.

In addition to basal insulin, you may be prescribed bolus insulin.

What is bolus insulin? 

Unlike basal insulin, bolus insulin, also called fast-acting insulin, short-acting insulin, or mealtime insulin, has a short duration and acts on after-meal blood sugar (also called postprandial blood sugar).

The carbohydrates you eat (rice, bread, pasta, fruits, etc.) contain sugars that are digested by the stomach and absorbed into the bloodstream as glucose. In people without diabetes, the pancreas immediately reacts and starts producing insulin to keep glycemia in the normal range. But when your pancreas does not produce enough insulin or no insulin at all, the glucose stays in your blood, causing a blood sugar spike (hyperglycemia).

Therefore, a bolus insulin dose is necessary to manage blood sugars after meals. However, not all diabetics need bolus insulin. Diabetic patients whose pancreas still produces insulin can correct their after-meal blood sugars with other types of medications, including metformin or other tablets. 

Bolus insulin must act quickly and is injected before, during, or right after meals. It can be administered with a pen, a syringe, or an insulin pump every time a person ingests carbohydrates (unless it’s to correct hypoglycemia).

Like basal insulin, there are different types of bolus insulins, including rapid-acting and short-acting insulins.

Short-acting insulin (bolus)

Short-acting insulin, also called regular insulin, covers insulin needs for meals eaten within 20 to 60 minutes after the injection. It starts working within about 30 minutes, peaks after 2-3 hours and stays in the bloodstream for 3 to 6 hours. It must be injected 30 minutes before each meal or carbohydrate intake (including snacks).  

Novolin-R, Humulin-R, and Velosulin (used for insulin pumps) are short-acting regular types of bolus insulin sold in the U.S. They are clear-looking insulins.

Rapid-acting insulin (bolus) 

Rapid-acting insulin is newer than regular insulin and works even faster. It covers insulin needs for meals eaten simultaneously with the injection. Their onset time is 10 to 15 minutes, with a peak of action at 30-90 minutes and a total duration of 2 to 4 hours. 

There are several types of rapid-acting bolus insulins, including aspart (marketed as Novolog and Fiasp), lispro (marketed as Humalog and Admelog), and glulisine (marketed as Apidra). These are also clear insulins. 

Depending on their type of diabetes, blood glucose management plan, lifestyle, and other factors, a person may be prescribed basal insulin, bolus insulin, or a combination of the two.

Related article: Can insulin go bad and how to tell if it has?

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Basal vs. Bolus Insulin: The Bottom Line

The key points to remember about the difference between basal and bolus insulins are:

  • They both lower blood sugar levels.
  • They target different “types” of blood glucose: basal insulin acts on fasting glucose, while bolus insulin acts on after-meal glucose.
  • They have different onset times, peak times, and durations.
  • Basal insulin is a slow background insulin, whereas bolus insulin is a fast-acting one.
  • Diabetics may be prescribed basal insulin, bolus insulin, or both types together.
  • They can sometimes be mixed together to reduce the number of injections.

Related article: Can you prefill insulin syringes?

The Basal-bolus Insulin Regimen

Basal-bolus insulin regimen is an intensive insulin therapy that combines injections of both basal and bolus insulin. It’s primarily used for people with Type 1 diabetes. Like any medical treatment, it has some advantages and inconveniences.

Pros:

  • It allows more flexibility with mealtimes
  • It reduces A1C further than other diabetes treatments

Cons:

  • It involves up to 4 injections of insulin a day
  • Patients must keep a supply of both types of insulin
  • There’s a risk of mistaking one insulin for the other 

With the new diabetes care technologies and advanced insulin pumps, which avoid the need for daily injections, the basal-bolus regimen is less and less frequent than it used to be. Instead, doctors now prefer automated insulin administration solutions coming close to an artificial pancreas that provide optimized blood sugar control and a better quality of life. 

Related article: How to sleep comfortably with an insulin pump?

Are you receiving basal-bolus insulin therapy? What are your thoughts on it? Do you find it convenient and efficient? Or would you instead use a smart insulin pump?

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