Insulin explained: what is insulin and how does it work?

If you live with insulin dependent diabetes, whether it is type 1, type 2, MODY, LADA or gestational diabetes, you know that this condition requires exogenous insulin to survive.

But what does insulin actually do? Why is there no insulin pill? Why can’t you drink it? What is the mechanism of action and how does it all work?

In this article, we will explain what insulin does when we take these injections daily.

What is insulin?

Insulin is a hormone produced by the beta cells of the pancreas. The body must convert food into energy and control blood sugar levels.

All people have insulin in their bodies, but people with diabetes either don’t make insulin, don’t produce enough insulin, or can’t use it properly (insulin resistance).

Insulin is considered the body’s main anabolic hormone, and its primary function is to facilitate the absorption of glucose from the bloodstream into the body’s cells (muscle and fat) as well as the liver.

When there is no (or not enough) insulin production in the body, a diagnosis of diabetes is made.


Why do we need insulin? 
Insulin is needed to move glucose from the bloodstream into the cells, supplying them with energy (and in excess it is stored as fat).  This energy is essential for the functioning of the body and brain. 
Glucose comes mainly from carbohydrate-rich foods such as bread, potatoes, and fruit, but when you’re short on carbs, glucose can also be made from fat and protein through a process called gluconeogenesis.
When people don’t have insulin, cells can’t metabolize glucose and it stays in the blood, resulting in high blood sugar. 
This is checked with an over-the-counter glucometer or HbA1c test, which measures your average blood glucose over the last 3 months.  You can do it yourself with a home HbA1c test.
Uncontrolled high blood sugar levels can quickly lead to diabetic ketoacidosis (DKA), a dangerous condition in which blood glucose levels are so high that the blood in the body becomes acidic;  it can become fatal if not properly (and quickly!) treated. 
When cells are deprived of glucose, typical symptoms of diabetes and/or DKA appear, such as: 

Weight loss
Extreme thirst
Extreme hunger
Frequent urination 
Blurred image
Fruity breath smell
Extreme fatigue 
Body pain 
Unconsciousness/death 

If you experience these symptoms for several days without relief, seek emergency medical attention or call 911 as these may be early signs of diabetes that will require immediate and professional healthcare. 

What does insulin do? 
Pancreatic beta cells sense a rise or fall in blood sugar and release insulin into the bloodstream accordingly. 
If someone eats an apple, but the beta cells sense that that person’s blood sugar is low, they will not release as much insulin as if they sensed that someone’s blood sugar is higher and eat the same apple. 
These microtiters happen every second of every day, and most people don’t even realize that their bodies are performing these functions! 
However, for people with diabetes, this whole process has to take place outside: people have to count carbohydrates, constantly check their blood sugar levels, and measure and dose their insulin accordingly. 
As the insulin moves from the bloodstream into the cells, the blood sugar (amount of glucose in the blood) will return to normal. 
However, people with diabetes risk hypoglycemia or low blood sugar if they take too much insulin. 
Taking insulin if you have diabetes is basically a constant tightrope between avoiding hyperglycemia (high blood sugar) and hypoglycemia. 
In people without diabetes, normal fasting blood sugar is below 99 mg/dL.  If you have diabetes, your ideal blood sugar level will depend on your lifestyle, age, activity level, life stage and health goals and will be determined by you and your doctor. 

How often do people with diabetes take insulin? 
People with insulin-dependent diabetes need insulin in their body 24 hours a day, 7 days a week, and they take it every day. 
Unlike most oral medications that can be taken once a day, people with insulin-dependent diabetes must take insulin for most of the food they eat and the drinks they drink, unless those foods and drinks do not contain carbohydrates. 
They take what is known as rapid-acting insulin (bolus insulin) with most meals.  Rapid-acting insulin usually stays in the bloodstream for 2 to 5 hours (depending on the brand and how your body responds to it). 
People with diabetes who use insulin pumps rely solely on rapid-acting insulin, where the insulin pump releases a very small amount of insulin in steady increments 24/7, mimicking the human pancreas.
More information on pump insulin can be found here: Pump insulin: what are the options?
If someone with diabetes is unwilling or unable to wear an insulin pump, they may opt for multiple daily injections (MDIs).  This is where they take both long-acting and fast-acting insulin.
Long-acting insulin (basal insulin) is usually administered once or twice a day (this type of insulin stays in the bloodstream much longer and is metabolized in small doses), along with rapid-acting insulin with meals and carbohydrates consumed. 
Long-acting insulin is needed (if one is not on an insulin pump) because it’s not just food that raises blood sugar.  Insulin is a hormone necessary for life, and even if you don’t eat anything for a day, you still need a minimal amount of insulin to live. 

Insulin side effects
Insulin’s major side effect is also the most well-known: low blood sugar!  Signs of taking too much insulin and low blood sugar include:

Trembling
Confusion 
Exploitation
Fast heartbeat 
Pale skin
Loss of consciousness 
In extreme cases, convulsions 

Rarely, someone may experience redness, swelling, or burning at the injection site, which could be a sign of an allergic reaction.
  More severe allergic reactions may include nausea or vomiting, and you should contact your doctor right away if you experience these while taking insulin. 
You can learn more about the side effects of insulin in our guide Insulin side effects: what you need to know.

summary 
If you live with insulin-dependent diabetes, you will need exogenous insulin (usually injections) to live.  This helps maintain blood glucose levels and prevents them from reaching dangerously high levels. 
Insulin is a hormone produced by the beta cells in the pancreas and helps move glucose from the bloodstream into the cells of the body, including muscle and fat cells, along with the liver. 
In people without diabetes, beta cells detect blood sugar levels and automatically release a steady amount of insulin into the bloodstream to help maintain blood sugar homeostasis. 
In people with diabetes, counting carbohydrates, testing blood sugar, and measuring and administering insulin must be done manually every day to prevent illness and death and to maintain normal blood sugar levels. 
Keeping your blood sugar levels in the right range can help prevent diabetes complications. 
In addition to insulin, people with diabetes should control their diet and exercise regularly to help maintain blood glucose levels. 
Always speak with your doctor to find the most effective combination of prescription medications, lifestyle changes, and insulin therapy to achieve your health goals.