Type 1 diabetes
Type 1 diabetes is thought to involve an interplay of genetic and environmental factors. You are at greater risk of developing type 1 diabetes if you have a relative (parent or sibling) who has been diagnosed with this disease. But environmental factors are also thought to play a role in triggering this disease, eg viral infections, and dietary factors during infancy. However, the exact mechanisms that influence the onset of this disease are unknown (2). In recent years the incidence of type 1 diabetes has been rising, especially among pre-school age children. Type 1 diabetes is also more common in northern European countries, eg Scandinavia, than Mediterranean countries, for reasons that are unclear.
Type 2 diabetes
Type 2 diabetes is also caused by a combination of genetic susceptibility (eg family history) and environmental factors (eg diet and lifestyle). The risk factors for developing type 2 diabetes include poor nutrition, being overweight or obese, having high blood pressure and having a sedentary lifestyle. Other risk factors include increasing age, ethnicity, socioeconomic status, and having a history of previous gestational diabetes, or polycystic ovary syndrome (3). The more risk factors you have, the greater your chance of developing this disease. Some of these risk factors are discussed in more detail below.
Obesity is closely associated with type 2 diabetes. Obese people are 7 times more likely to develop type 2 diabetes than people with a healthy weight, and overweight people are 3 times more likely to develop the disease (1). Studies have also found that men and women with a larger waist size are five and three times, respectively, more likely to have diabetes than those without a large waist circumference (3). Central obesity is particularly diabetogenic.
A whopping 90 % of adults with type 2 diabetes aged 16-54 are overweight or obese in the U.K. Being overweight or obese is the main lifestyle factor that we can change to reduce the risk of type 2 diabetes (4, 5). In the U.K, 1 in 5 adults are overweight and 1 in 15 people are obese (6) and the longer period of time in which such people remain overweight or obese the more likely they will be to develop this disease (7).
Most cases of obesity are a result of physical inactivity and excessive caloric intake, although a few people may become obese due to genetic or medical reasons.
Other risk factors
Type 2 diabetes is associated with increasing age- a lifetime of churning out insulin leads to exhaustion and dysfunction of beta cells. Being older than 40 years, or older than 25 years for some black and minority ethnic groups, increases the risk of developing type 2 diabetes (25).
Tobacco smoking is implicated to be a causal factor in type 2 diabetes. If you are a smoker, your risk of developing type 2 diabetes is 30-40 % higher compared to a non-smoker, and the more cigarettes you smoke the more likely you are to get type 2 diabetes (26). And people with diabetes who smoke are more likely than non-smokers to have trouble with regulating their insulin doses and with controlling their disease (25). Smoking is also related to the enhanced risk of complications from diabetes (27).
Developing type 2 diabetes is strongly associated with ethnicity, so that if you are from an ethnic background such as south Asia, China, or Afro-Caribbean, or black African and aged 25-39, your risk of developing diabetes increases. This is due to both genetic and environmental factors. A health survey in the UK (28) found that all minority ethnic groups (except for being Irish) have a higher risk of being diagnosed with type 2 diabetes than the rest of the population. Furthermore, type 2 diabetes affects people of South Asian, African-Caribbean, Chinese or black African descent up to ten or more years earlier than white Europeans (29, 30).
Deprivation or being in a lower socioeconomic group is also associated with type 2 diabetes, with people most deprived being at 40% greater risk of developing this disease (31).