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What is insulin and why is it important?

This article describes what insulin does and explains why it's is important in diabetes, controlling the right amount of glucose in our blood.

When we eat food, the carbohydrates (sugars) that we eat are broken down in our digestive system to produce glucose. This glucose has an important role to play in our health, as it is required to provide the energy our cells need to live and function.

Glucose levels in the blood

If we don’t have enough glucose entering our cells we are at risk from harmful conditions like diabetic ketoacidosis (DKA) which can be life-threatening as the cells are starving even if blood glucose concentrations are high. On the other hand, often we eat too much sugar and have too much glucose in our blood.

This is bad news for us, because too much glucose damages our cells and organs, causing them to not work so well. Diabetes is a disease characterised by high blood glucose levels (hyperglycaemia). So, it is really important that our bodies are able to control the amount of glucose in our blood.

Controlling glucose levels

Our bodies control the amount of glucose in our blood by using two teams of hormones.


The first team is led by the hormone insulin. Insulin acts to decrease the amount of glucose in our blood, by signalling to cells to take up all the glucose they can find and to either store it or use it.
The second team is made up of hormones like glucagon and cortisol, and this team acts to increase the amount of glucose in our blood.

Hormone teams acting as messengers

It is useful to think about insulin and other hormones as messengers. The liver is a key organ in glucose control. Insulin signals to the liver to take up glucose and store it when blood glucose concentrations are too high. Glucagon and cortisol signal to the liver to release stored glucose and make new glucose.
Imagine if …
  • Insulin @iloveinsulin has a social media account and it sends a message to its follower the liver @theliver
  • Glucagon @ihateinsulin has a social media account and it sends a message to its follower the liver @theliver
  • The liver @theliver has a social media account and it sends messages to its followers Insulin @iloveinsulin and Glucagon @ihateinsulin
Our bodies are constantly sensing how much glucose is in the blood, and increasing or decreasing the two teams that control the levels of glucose.
These teams act quickly so that we can deal with rapidly changing levels of glucose, such as after a meal.

Why is glucose control important?

The primary diabetes outcome is glycaemic control, as measured by a blood test (glycosylated haemoglobin or HbA1c) that indicates average plasma glucose for the previous 2-3 months.

Poor glycaemic control has been related to short-term consequences such as hypoglycaemia and diabetic ketoacidosis (DKA), as well as serious health consequences later in life such as limb amputation, retinopathy, and renal disease.

Hyperglycaemia means high blood glucose levels. These are normally defined as those which are persistently above 11.1mmol/L. (200mg/dl). Hypoglycaemia is where blood glucose levels are under 4mmol/L. (72mg/dl).

Completion of recommended self-care tasks is considered critical to glycaemic control, with the primary tasks which help to maintain glycaemic control, such as monitoring blood glucose levels, injecting insulin, and dosing insulin according to meter results or other factors, needing to be carried out several times per day, often around mealtimes in varied contexts and locations.

© University of Southampton
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Understanding Insulin

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