Causes of type 1 diabetes

In type 1 diabetes, the cells in the pancreas that make insulin are destroyed, causing a severe lack of insulin. This is usually thought to be the result of the body attacking and destroying its own cells in the pancreas, known as an autoimmune reaction.

It isn't clear why this happens, but a number of explanations and possible triggers have been proposed. These include:

Infection with a specific virus or bacteria
Exposure to food-borne chemical toxins
Exposure as a very young infant to cow's milk, where an as yet unidentified component triggers the autoimmune reaction
However, these are only hypotheses and are not proven causes.

As with other autoimmune diseases, an underlying genetic disposition seems to play a part, leaving some people more vulnerable to these triggers.

In rare cases, damage to the pancreas by tumours, toxins or injury (including surgery), can also lead to type 1 diabetes.

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Causes of type 2 diabetes

Development of type 2 diabetes is usually multifactorial - that is, several factors combine to cause it. The most important of these is genetics. Children of people with type 2 diabetes have a one in three chance of developing the condition themselves.

In this type of diabetes, the receptors on cells in the body that normally respond to the action of insulin fail to be stimulated by it. This is known as insulin resistance.

In response to this, more insulin may be produced and this overproduction exhausts the insulin-manufacturing cells in the pancreas. There is simply insufficient insulin available and the insulin that is available may be abnormal and so doesn't work properly.

The following risk factors increase the chances of someone developing type 2 diabetes:

Increasing age
Obesity
Physical inactivity
Rarer causes of type 2 diabetes include:

Certain medicines
Pregnancy (gestational diabetes)
Any illness or disease that damages the pancreas and affects its ability to produce insulin, such as pancreatitis