Updated 05 September 2018

Causes of diabetes

The causes of type 1, type 2 and gestational diabetes differ, and despite popular belief, none of them are directly caused by eating too much sugar.

The underlying causes of diabetes vary by type.

Causes of type 1 diabetes

Type 1 diabetes occurs when the immune system attacks and destroys the insulin-producing cells in the pancreas (the beta cells). As a result, the body is left without enough insulin to function normally (i.e. it becomes insulin deficient). This is called an autoimmune reaction, because the body attacks itself and produces antibodies to its own insulin-producing cells, thereby destroying them.

Researchers don’t exactly know why this process is activated in some people. Apart from a possible genetic predisposition, the following triggers may be involved:

  • Viral or bacterial infection
  • Chemical toxins in food

When a person with type 1 diabetes develops symptoms, most of the beta cells in the pancreas have already been destroyed.

Causes of type 2 diabetes

The causes of type 2 diabetes are multifactorial and complex. But even though there is no single cause, there are some well-known predisposing factors – the most overwhelming being obesity and a family history of type 2 diabetes.

Type 2 diabetes is the result of both insulin resistance (when the cells don’t respond well to insulin and can’t easily take up glucose from the blood) and progressive beta-cell damage, resulting in too little insulin being secreted by the pancreas.

By the time a person is diagnosed with type 2 diabetes, up to 50% of the beta cells in the pancreas have usually been damaged. In fact, these cells may have been declining for up to 10 years before the diagnosis. Along with raised blood pressure and elevated cholesterol levels, this predisposes the person to arterial damage years before diabetes is diagnosed. So, at the time of diagnosis, the person is already at risk for cardiovascular disease (CVD).

Your risk of getting type 2 diabetes is higher if:

  • There’s a history of diabetes in your family
  • You’re middle-aged or older
  • You’re overweight or obese
  • You’re middle-aged and have high blood pressure (hypertension)
  • You’ve given birth to a child weighing more than 4.5kg, was diagnosed with gestational diabetes or have/had polycystic ovarian syndrome (PCOS)

Type 2 diabetes is also associated with insufficient physical activity, poor diet and extra weight carried around the waist.

Causes of gestational diabetes

It isn’t known exactly why some women develop gestational diabetes, but there is often a positive family history of diabetes.

The woman’s weight may also play a role. Changing hormone levels and weight gain are part of a healthy pregnancy, but both changes make it more difficult for the body to keep up with its need for insulin. This may lead to gestational diabetes. As pregnancy progresses, the placenta also produces insulin-blocking hormones, which might result in a woman’s blood-glucose levels becoming elevated if there isn’t enough insulin to counter this effect.

Information supplied by Jeannie Berg, diabetes educator and Chairperson of the Diabetes Education Society of South Africa (DESSA), and reviewed by Dr Joel Dave (MBChB PhD FCP Cert Endocrinology), Senior Specialist in the Division of Diabetic Medicine and Endocrinology, University of Cape Town. August 2018.

Read more:

Symptoms of diabetes


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Dr. May currently works as a fulltime endocrinologist and has been in private practice since 2004. He has a variety of interests, predominantly obesity and diabetes, but also sees patients with osteoporosis, thyroid disorders, men's health disorders, pituitary and adrenal disorders, polycystic ovaries, and disorders of growth. He is a leading member of several obesity and diabetes societies and runs a trial centre for new drugs.

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