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.
What defines overweight and obesity?
Body mass index (BMI) is the best assessment of weight and compares your weight in relation to your height. BMI is calculated by the following equation:
This value is used to determine if you are in the:
As a person’s BMI increases so does their risk of developing type 2 diabetes. For example, a review of 89 studies on weight related diseases found that, compared with men and women in the normal weight range, men with a BMI of 30 or higher had a seven-fold higher risk of developing type 2 diabetes, and women with a BMI of 30 or more had a 12-fold higher risk. (8)
Waist circumference (WC) is a measure of the accumulation of body fat around the waist, or abdominal fat. High levels of this “belly” fat can also predict future ill health and it is associated with type 2 diabetes, high blood pressure, and cardiovascular disease.
Why is abdominal fat so bad?
Abdominal fat cells in obese or overweight people become sinister organs, and are different from peripheral fat cells (fat cells in the legs, trunk or arm). They release pro-inflammatory chemicals (chemicals causing inflammation), which make the body less sensitive to the insulin it produces by disrupting insulin responsive cells and their ability to respond to insulin (9), (10). As the percentage of abdominal fat increases, so does the level of insulin resistance. When beta cell function is also disrupted, then blood glucose levels cannot be controlled (11).
Physical inactivity and diabetes
There is a strong association between type 2 diabetes, an unhealthy diet (see Nutrition below) and a sedentary lifestyle. People who are physically inactive are at an increased risk of developing type 2 diabetes, and people with diabetes tend to be more sedentary than non-diabetic people (12).
The more of a sedentary lifestyle you lead (as measured by the number of hours watching television) the higher the risk of developing type 2 diabetes. A recent study analysing results of several population studies found that for every two hours per week of watching t.v the risk of developing type 2 diabetes increased by 20% (13). On the other hand, physical activity plays a key role in prevention and treatment of diabetes. Brisk walking for one hour, for example, reduces the risk by 34% (14, 15) see Prevention.
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).
Conditions that increase type 2 diabetes risk
Prediabetes is a term used to describe blood glucose levels that are above the normal optimal range, but still lower than the cut-off used to define diabetes. Although having prediabetes increases the risk of progression to type 2 diabetes, it is not a certainty that the disease will develop as lifestyle changes (nutrition and exercise) can correct blood glucose levels and reverse this risk.
This phrase refers to a group of health conditions that put you at risk of developing type 2 diabetes, as well as heart-related problems (cardiovascular disease).
Metabolic syndrome is thought to be due to increasing age, genetics and lifestyle and like diabetes and prediabetes, its outcome can be improved by having a healthier lifestyle.
If you have a combination of three or more of these conditions, then you have metabolic syndrome:
High blood pressure
High fasting blood glucose levels
High levels of triglycerides or LDL-cholesterol (“bad fats”)
Low levels of HDL cholesterol (“good fats”)
Abdominal fat or high BMI
— May Meleigy
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- Kodama S, Horikawa C, Fujihara K, et al. Quantitative relationship between bodyweight gain in adulthood and incident type 2 diabetes: a meta-analysis. Obes Rev 2014;15 (3):202-14. doi: 10.1111/obr.12129. Epub 2013 Oct 25
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- Hamer M, Bostock S, Hackett R, et al. Objectively assessed sedentary time and type 2 diabetes mellitus: a case-control study. Diabetologia 2013;56 (12):2761-2.
- Grontved A, Hu FB. Television viewing and risk of type 2 diabetes, cardiovascular disease, and all-cause mortality: a meta-analysis. JAMA. 2011;305:2448-55.
- Tanasescu M, Leitzmann MF, Rimm EB, Hu FB. Physical activity in relation to cardiovascular disease and total mortality among men with type 2 diabetes. Circulation. 2003.
- Hu FB, Sigal RJ, Rich-Edwards JW, et al. Walking compared with vigorous physical activity and risk of type 2 diabetes in women: a prospective study. JAMA. 1999; 282:1433-9
- de Munter JS, Hu FB, Spiegelman D, Franz M, van Dam RM. Whole grain, bran, and germ intake and risk of type 2 diabetes: a prospective cohort study and systematic review. PLOS Med. 2007;4:e261.
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