Causes

Type 2 diabetes is primarily the result of two interrelated problems:

• Cells in muscle, fat and the liver become resistant to insulin. Because these cells don't interact in a normal way with insulin, they don't take in enough sugar.
• The pancreas is unable to produce enough insulin to manage blood sugar levels.

Exactly why this happens is unknown, but being overweight and inactive are key contributing factors.

How insulin works

Insulin is a hormone that comes from the gland situated behind and below the stomach (pancreas). Insulin regulates how the body uses sugar in the following ways:

• Sugar in the bloodstream triggers the pancreas to secrete insulin.
• Insulin circulates in the bloodstream, enabling sugar to enter your cells.
• The amount of sugar in your bloodstream drops.
• In response to this drop, the pancreas releases less insulin.

The role of glucose

Glucose — a sugar — is a main source of energy for the cells that make up muscles and other tissues. The use and regulation of glucose includes the following:

• Glucose comes from two major sources: food and your liver.
• Glucose is absorbed into the bloodstream, where it enters cells with the help of insulin.
• Your liver stores and makes glucose.
• When your glucose levels are low, such as when you haven't eaten in a while, the liver breaks down stored glycogen into glucose to keep your glucose level within a normal range.

In type 2 diabetes, this process doesn't work well. Instead of moving into your cells, sugar builds up in your bloodstream. As blood sugar levels increase, the insulin-producing beta cells in the pancreas release more insulin. Eventually these cells become impaired and can't make enough insulin to meet the body's demands.

In the less common type 1 diabetes, the immune system mistakenly destroys the beta cells, leaving the body with little to no insulin.