What is Insulin?

What is Insulin?

Insulin is an important hormone that is secreted by beta cells in the pancreas. 

The main role of insulin is to regulate glucose levels in the bloodstream, ensuring metabolic balance by promoting glucose storage in the liver, muscles, and adipose tissue1.

Normal Function of Insulin

Shortly after we eat, our blood glucose levels rise as the food is broken down by our digestive system. Under normal conditions, the pancreas then releases insulin to help glucose enter the body's cells. Within the cell, glucose is converted into energy that is vital for life. Insulin also signals the liver to store glucose for later use, an important adaptation we have to maintain energy even while in a fasted state. Insulin is therefore crucial for maintaining the body's energy balance2.

In individuals with type 2 diabetes mellitus (T2DM), insulin's normal function is impaired, leading to a lack of effective glucose storage. This results in high blood glucose levels, known as hyperglycemia4.

T2DM is characterised by defects in insulin secretion and insulin action, leading to persistent elevation of glucose levels in the blood stream, (as shown in the diagram below). Extended periods of hyperglycaemia can contribute to harm in blood vessels, nerves, and organs, elevating the risk of multiple complications, including heart disease, stroke, kidney disease, and vision problems5. These noteworthy health implications, stemming from an poor insulin response to glucose, underscore the critical importance of effectively managing T2DM as a serious chronic health condition.

Healthy vs Type 2 Diabetes

Fig. 1 This diagram illustrates the contrasting responses to blood glucose levels in healthy individuals and those with Type 2 diabetes. In healthy individuals, elevated blood glucose triggers insulin receptors, activating glucose transporters. This process efficiently removes glucose from the bloodstream, restoring glucose levels to the normal physiological range. Conversely, in Type 2 diabetes, insulin receptors become desensitised or fail to respond adequately to glucose. This malfunction results in a persistent elevation of blood glucose levels. The impaired insulin signalling in T2DM disrupts the usual regulation, leading to chronic hyperglycemia. Created in


In summary, the insulin hormone is a key player in maintaining the body's energy balance and regulating blood sugar levels. Inadequate insulin or insulin that does not work as effectively as it should is a key feature of T2DM.

December 14, 2023
Written by
Dr. Harriet Lester
Reviewed by
Dr. Laura Falvey


  1. Rahman, Md S., et al. 2021. Role of Insulin in Health and Disease: An Update. International Journal of Molecular Sciences, 22(12).
  2. Norton, L., Shannon, C., Gastaldelli, A., & DeFronzo, R. A. 2022. Insulin: The master regulator of glucose metabolism. Metabolism, 129, 155142.
  3. Rachdaoui, N. 2020. Insulin: The Friend and the Foe in the Development of Type 2 Diabetes Mellitus. International Journal of Molecular Sciences, 21(5), 1770. 
  4. White Jr, J. R., Davis, S. N., Cooppan, R.,, 2003. Diabetes Consortium Medical Advisory Board. Clarifying the role of insulin in type 2 diabetes management. Clinical diabetes, 21(1), 14-21.
  5. Deshpande, A. D., Harris-Hayes, M., & Schootman, M. 2008. Epidemiology of Diabetes and Diabetes-Related Complications. Physical Therapy, 88(11), 1254-1264. 

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