Updated 20 February 2017

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.


A poor diet, high in fat, carbohydrates and refined, sugary foods can contribute to type 2 diabetes by causing weight gain, which is where the misconception probably comes from.

Causes of type 1 diabetes

At the time a person with type 1 diabetes experiences symptoms, a significant percentage of the beta cells in the pancreas have already been destroyed.

This destruction is as a result of an autoimmune process in which the body produces antibodies to its own insulin-producing cells.

A widely accepted theory is that there is a genetic tendency for the disease, which is then triggered by an environmental event such as a viral infection. Inflammation of the pancreas called insulitis then occurs.

Eventually an alteration in the surface of the beta cell occurs so that it is no longer recognised as “self” – part of the body – but is perceived by the immune system to be a foreign cell or “non-self”.

The final step is the development of an immune response. The end result is the destruction of the beta cell and the development of diabetes.

Causes of type 2 diabetes

Factors causing type 2 diabetes are complex, and although there isn’t a single cause, there are some well-known predisposing factors.

Essentially Type 2 diabetes is caused by both insulin resistance and progressive beta cell damage resulting in too little insulin being secreted by the pancreas.

 By the time a patient is diagnosed with type 2 diabetes, up to 50% of the cells in the pancreas that make insulin (the beta cells) have been damaged.

However, the decline in the number of the cells with the metabolic consequences of insulin resistance might have been present (and asymptomatic) for up to 10 years before diagnosis.

Along with hypertension (raised blood pressure) and elevated cholesterol, this predisposes to arterial damage years before the diagnosis of the diabetes. So, at the time of diagnosis of diabetes, you are already at risk for cardiovascular disease.

Your risk of getting type 2 diabetes is higher if:

- There is a history of diabetes in your family

- You are middle-aged and older

- You are overweight

- You are middle-aged and have high blood pressure

- You have given birth to a child of more than 4.5 kg, had gestational diabetes or have/had Polycystic Ovarian Syndrome

Type 2 diabetes is also associated with lifestyle factors like:

- Insufficient physical activity

- Poor diet

 - Body type where extra weight is carried around the waist. Insulin resistance is the main metabolic abnormality leading to the development of type 2 diabetes.

The most recent research suggests that type 2 diabetes can be seen as a consequence of a series of physiological abnormalities, each of which makes the person vulnerable to subsequent disruption of normal glucose metabolism.

Causes of gestational diabetes

It is not known why some women develop gestational diabetes, but a positive family history of diabetes is often found in these patients. 

Changing hormones 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, which may lead to diabetes.

As pregnancy progresses, the placenta produces insulin-blocking hormones and this might result in the blood sugar becoming elevated if there is not enough insulin to counter this effect.

 Gestational diabetes usually only develops during the second half of pregnancy.

Complications of diabetes

1. Eye damage to the back of the eye (retinopathy) or cataracts. Diabetes is the leading cause of blindness in developed countries in the western hemisphere.

2. Protein leakage from the kidney, kidney damage and kidney failure. Diabetes (with hypertension) is the leading cause of kidney failure in the world.

3. Nerve damage giving rise to pain, pins and needles and numbness in the peripheries; damage to any nerve in the body

4. Erectile dysfunction as a result of both arterial damage to the penis and/or nerve damage

5. Coronary artery disease giving rise to heart attacks

6. Stroke

7. Peripheral arterial disease, resulting in ulcers or pain in the legs and in some cases amputation of toes and lower limbs

8. General complications like arthritis, skin conditions, fatigue, susceptibility to infection etc.

Read more:

Treating gestational diabetes

Treating type 1 diabetes

Treating type 2 diabetes

Reviewed by Dr Hilton Kaplan, MB BCH (Rand), FCP(SA), MMed(UCT), Specialist Endocrinologist and Physician (March 2016)


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Diabetes expert

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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