Overweight and obesity are the most important risk factors for diabetes

Risk factors for diabetes can be divided in 'biological and personal factors' and 'health behaviours'.

Biological and personal factors (WHO, 2003b; IDF, 2006a; Baan et al., 2005):

• Overweight and obesity, especially central obesity (accumulation of fat around the waist), are the strongest risk factors for diabetes mellitus. In the Netherlands, for example, the population attributable risk (PAR) of being overweight and obese, for diabetes incidence, is 66%. This means that 66% of new diabetes cases are attributable to overweight (28%) or obesity (38%) (Baan et al., 2005).
• Certain genes are associated with higher risk of developing diabetes. This genetic predisposition is more important for the type 2 than for the type 1 diabetes. However, diabetes is a multifactorial disease: genes alone are not enough, environmental factors are needed to trigger the onset of disease.
• GDM (gestational diabetes mellitus): children of mothers with diabetes are at a higher risk of developing type 2 diabetes. Breastfeeding has a protective effect for children of both, diabetic and non-diabetic women.
• Prediabetes, including people with Impaired Glucose Tolerance (IGT) and Impaired Fasting Glucose (IFG) have blood glucose concentrations above the normal range, but below the diagnostic criteria for diabetes. IGT and IFG are called pre-diabetes but they are also a risk factor for developing diabetes.

Health behaviours (WHO, 2003b; IDF, 2006a; Baan et al., 2005):

• Sedentary lifestyle favours the development of diabetes type 2, while physical activity significantly reduces the risk.
• Dietary factors:
• A diet high in fat and saturated fatty acids is associated with a higher risk of impaired glucose tolerance, higher fasting glucose concentrations and higher insulin levels.
• A high intake of dietary fibre (non-starch polysaccharides) from wholegrain cereals, vegetables and fruits protects against the development of diabetes.
• Smoking increases the risk of developing diabetes.

Risk factors interact

All of these risk factors operate in complex interaction, e.g. health behaviours interact with genetic predisposition to result in overweight, which in turn may lead to diabetes. Often a combination of environmental risk factors is present in one individual.

Strength of evidence on lifestyle factors and risk of developing type 2 diabetes