Diabetes - Risk factors

The risk of type 1 or type 2 diabetes developing is affected by both geneticRelating to the genes, the basic units of genetic material. and environmental factors.

Type 1 diabetes

Genes

Your genes are important in determining your risk of developing type 1 diabetes.[1] For example, if one twin has type 1 diabetes, there is almost a one in three chance that the other twin will also have the condition.[2]

Environmental factors

Several environmental factors may also increase the risk of type 1 diabetes. For example, it has been suggested that reduced exposure to bacteriaA group of organisms too small to be seen with the naked eye, which are usually made up of just a single cell. and other microorganismsOrganisms that are too small to be seen with the naked eye, such as bacteria and viruses. in childhood may prevent the immune systemThe organs specialised to fight infection. from developing properly, increasing the risk of autoimmuneAny condition caused by the body’s immune response against its own tissues. conditions such as type 1 diabetes. It is also thought that some virusesMicrobes that are only able to multiply within living cells., such as mumpsA viral infection common in schoolchildren. It may cause fever, vomiting and swelling of the parotid glands, the largest salivary glands., cytomegalovirusA member of the herpes group of viruses. and Epstein-Barr virusA microbe that is only able to multiply within living cells., may play a part.[1]

Dietary factors may also have a role. For instance, infants who are given cow's milk rather than being breastfed may have an increased risk of developing type 1 diabetes.[1]

Stress may also influence hormoneA substance produced by a gland in one part of the body and carried by the blood to the organs or tissues where it has an effect. secretion and immune activity, which may in turn increase the risk of type 1 diabetes.[1]

There have been reports that depression may play a role in the development of the condition, as it affects up to a fifth of patients with diabetes; whether this may contribute to type 1 or type 2 diabetes, or both, is not known.[3]

Type 2 diabetes

Important risk factors for type 2 diabetes include:

  • Obesity
  • Age
  • Ethnicity
  • Family history.

Many genes that increase the risk of type 2 diabetes have been identified. This means that your family history is very important. Still, even if you have the genes that indicate you have an increased risk, it is your lifestyle (diet and exercise) that largely determines whether or not the condition will develop.[1]

Type 2 diabetes, or the abnormal bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. glucoseA simple sugar that is an important source of energy in the body. levels that may precede it, is often associated with abdominal obesityObesity centred around the abdomen, resulting in a high waist circumference., high blood pressure and abnormal lipidOne of a group of compounds that are an important energy source. levels. Because these features occur together so often, they are sometimes referred to collectively as the 'metabolic syndromeThe combination of insulin resistance, abdominal obesity, high blood pressure and disordered blood lipids that increases the risk of cardiovascular disease.'.[1]

Obesity

Research has shown that being overweight, as suggested by having a high body mass indexA measure of whether a person’s weight is normal, too high or too low. It is calculated by dividing their weight in kilograms by the square of their height in metres. (BMI), increases the risk of type 2 diabetes.[4,5] Obesity in general contributes to the development of type 2 diabetes, and abdominal obesityObesity centred around the abdomen, resulting in a high waist circumference. in particular appears to be especially likely to increase the risk.[4]

Abdominal obesityExcess accumulation of fat in the body. is an important component of metabolic syndromeThe combination of insulin resistance, abdominal obesity, high blood pressure and disordered blood lipids that increases the risk of cardiovascular disease., the clustering of cardiovascular risk factors that also increases the risk of developing type 2 diabetes if this condition is not present already.

The International Diabetes Federation produced guidelines on the definition of the metabolic syndromeThe combination of insulin resistance, abdominal obesity, high blood pressure and disordered blood lipids that increases the risk of cardiovascular disease. in 2005. These stated that women were at risk if they had a waist circumference of 80cm (31in) or more, while the waist circumference cut-off values for men depended on their ethnicity.

For example, the guidelines stated that men of European descent were at risk if they had a waist circumference of 94cm (37in) or more, whereas men of South Asian origin were at risk with a waist circumference of just 90cm (35in).[6] This is because ethnicity (see below) can also influence risk.

Physical inactivity

People who are not physically active usually have a higher level of insulin resistanceA reduced response of the body to the hormone insulin, resulting in raised blood glucose levels. than active people, even if they are equally overweight.[1] Most people with type 2 diabetes are much less active than other people.[7]

Even so, it is thought that obesityExcess accumulation of fat in the body. plays more of a role than lack of physical activity in increasing the risk of type 2 diabetes, although both factors are important.[5,8]

Diet

The composition of a person's diet is also important and has been found to be associated with diabetes risk whether or not the person is obese.[9] Refined carbohydratesA group of compounds that are an important energy source, including sugars and starch. may increase the body's demand for insulinA hormone produced by the beta cells of the pancreas that acts to lower blood glucose levels., and high-fatOne of the three main food constituents (with carbohydrate and protein), and the main form in which energy is stored in the body. foods may increase free fatty acid levels in the bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid., so increasing insulin resistanceA reduced response of the body to the hormone insulin, resulting in raised blood glucose levels..[1]

Fats in your diet

Genes

Genes may play an even bigger role in type 2 than in type 1 diabetes[1]; in almost all cases, if one of a pair of identical twins has the condition, so will the other.[2]

Family history is therefore very important.[2,10] If any of your relatives have type 2 diabetes, you will have a higher risk of developing it yourself; and the closer the relative, the higher this risk.

However, unless you have an identical twin, having close relatives with type 2 diabetes does not mean that you will definitely develop the condition as well.[10]

Ethnicity

People who are of South Asian, African, African-Caribbean and Middle Eastern descent are at a higher risk of developing diabetes than Caucasian people.[1,6]

Other risk factors

As well as increasing age,[1] several other factors may raise your risk of developing type 2 diabetes, although the evidence for these varies. It has been suggested that higher levels of ironAn element present in haemoglobin in the red cells. in the body may increase the risk of type 2 diabetes, independent of other risk factors[11]; the same has also been suggested for snoring.[12]

References: 
  1. Boon NA, Colledge NR and Walker BR. Davidson's Principles and Practice of Medicine Churchill Livingstone Elsevier. 2006; 20th edition.
  2. Longmore M, Wilkinson I and Török E. Oxford Handbook of Clinical Medicine 2002; 5th edition.
  3. Symptoms of depression as a risk factor for incident diabetes: findings from the National Health and Nutrition Examination Epidemiologic Follow-up Study, 1971-1992. Carnethon MR, Kinder LS, Fair JM et al. Am J Epidemiol. 2003;158:416-23.
  4. Comparison of abdominal adiposity and overall obesityExcess accumulation of fat in the body. in predicting risk of type 2 diabetes among men. Wang Y, Rimm EB, Stampfer MJ et al. Am J Clin Nutr. 2005;81:555-63.
  5. Adiposity compared with physical inactivity and risk of type 2 diabetes in women. Rana JS, Li TY, Manson JE et al. Diabetes Care. 2007;30:53-8.
  6. International Diabetes Federation. www.idf.org/webdata/docs/MetSyndrome_FINAL.pdf Accessed April 29, 2009.
  7. Physical activity and the incidenceThe number of new episodes of a condition arising in a certain group of people over a specified period of time. of type 2 diabetes in the Shanghai women's health study. Villegas R, Shu XO, Li H et al. International Journal of Epidemiology. 2006;35:1553-62.
  8. Physical activity in US adults with diabetes and at risk for developing diabetes, 2003. Morrato EH, Hill JO, Wyatt HR et al. Diabetes Care. 2007;30:203-9.
  9. A prospective study of overall diet quality and risk of type 2 diabetes in women. Fung TT, McCullough M, van Dam RM et al. Diabetes Care. 2007;30:1753-7.
  10. Type 2 diabetes and maternal family history. Bjørnholt JV, Erikssen G, Liestøl K et al. Diabetes Care. 2000;23:1255-9.
  11. Body ironAn element present in haemoglobin in the red cells. stores in relation to risk of type 2 diabetes in apparently healthy women. Jiang R, Manson JE, Meigs JB et al. JAMA. 2004;291:711-7.
  12. Snoring as a risk factor for type II diabetes mellitusDisordered energy metabolism and high levels of glucose in the blood owing to a lack of insulin, or poor response of the body to insulin.: a prospective study. Al-Delaimy WK, Manson JE, Willett WC et al. Am J Epidemiol. 2002;155:387-93.