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(see Box 4.2). Such people have a 20% risk of developing diabetes. Whilst many are currently living in the economically developed nations, less industrialised countries are developing similar lifestyle patterns and catching up (Table 4.2).

Silent damage

Type 2 diabetes tends to develop gradually over long periods of time. Complications may be established, or even advanced, at the time of diagnosis. These affected up to 50% of newly diagnosed type 2 patients in the UKPDS Study. Macrovascular complications may precipitate awareness of a previously unrecognised diagnosis. An individual may present with an acute myocardial infarction or stroke, and be diagnosed with diabetes during his/her first admission to hospital. Alternatively, the patient may very gradually develop symptoms of thirst and polyuria. Established complications such as retinopathy or albuminuria may have progressed silently over the preceding years.

Box 4.1 The metabolic syndrome

Type 2 diabetes is a complex metabolic disorder, lying at one end of a spectrum of progressively impaired glucose regulation, insulin resistance, and beta cell insufficiency. Central obesity, hypertension and dyslipidaemia usually accompany this constellation and together represent the 'metabolic syndrome'. Identifying this condition gives us an opportunity to delay the onset of diabetes and control the other cardiovascular risk factors that are part of the syndrome

Should we screen the population for diabetes?

The early phase of diabetes in which people are asymptomatic but nevertheless developing serious and preventable complications would argue strongly in favour of a screening programme. But whilst there are a number of identifiable factors that raise an individual's risk, most of them (such as age and body mass index) are very non-specific, so that a screening programme would need to involve a large proportion of the adult population. A further issue is the choice of screening test. Random blood glucose levels are relatively non-specific, leading to large numbers requiring follow-up depending on the threshold used. Fasting levels are more specific but may miss people whose abnormal glucose regulation affects their response to carbohydrate challenge rather than their fasting levels. This is more likely to apply to South Asian people. Such individuals will only be identified by an oral glucose tolerance test (OGTT). The OGTT is considered the 'gold standard' but is not always reproducible. Patients with impaired glucose tolerance can only be identified using OGTT.

Screening for raised cardiovascular risk

The overlap between type 2 diabetes, impaired glucose regulation and raised cardiovascular risk has, in the UK, resulted in a shift away from diabetes screening, and towards individualised cardiovascular risk assessments. This is intended for those without either established vascular disease or diabetes in the over-40 age group. These

Box 4.2 The metabolic syndrome: International Diabetes Federation definition

Central obesity (see Table 4.2) plus any two of the following four factors:

Raised Triglyceride level: >1.7 mmol/l, or specific treatment for this lipid abnormality

Reduced HDL cholesterol: <40 mg/dl (1.03 mmol/l*) in males and <50 mg/dl (1.29 mmol/l*) in females, or specific treatment for this lipid abnormality

Raised blood pressure: systolic BP >130 or diastolic BP >85 mm Hg, or treatment of previously diagnosed hypertension Raised fasting plasma glucose >5.6 mmol/l, or previously diagnosed type 2 diabetes

*If above 5.6 mmol/l, an oral glucose tolerance test is strongly recommended but is not necessary to define the presence of the syndrome

Table 4.2 Ethnicity specific definition of central obesity.

Country/Ethnic group Waist circumference

Europids Male >94cm

In the USA, the ATP III values (102 cm male; 88 cm female) are likely to continue Female >80cm to be used for clinical purposes

South Asians, Chinese and Japanese Male >90cm

Based on a Chinese, Malay and Asian Indian population Female >80cm

Ethnic South and Central Americans Use South Asian recommendations until more specific data are available

Sub-Saharan Africans Use European data until more specific data are available

Eastern Mediterranean and Middle East (Arab) populations Use European data until more specific data are available

If BMI is >30kg/m2, central obesity can be assumed and waist circumference does not need to be measured. Adapted from: International Diabetes Federation ethnicity-specific definitions of central obesity.

assessments include a random blood glucose estimation followed by further investigation of borderline or raised levels. They also involve the use of cardiovascular risk algorithms using the known risk factors, together with other relevant information such as ethnicity, family history, body mass index, waist circumference and random plasma glucose (followed if necessary by fasting plasma glucose or OGTT). This serves as a screening programme for vascular risk factors including diabetes and impaired glucose regulation.

Preventing diabetes in those at risk

Can we delay the onset of diabetes, or prevent it altogether?

The opportunity to reduce cardiovascular risk in individuals with 'pre-diabetes' is one benefit of identifying impaired glucose regulation. Another is the opportunity to delay or prevent progression to diabetes itself. The Diabetes Prevention Programme in the USA (Diabetes Prevention Programme Research Group 2002), and the Finnish Diabetes Prevention Study (Tuomilehto etal. 2001) both found a 58% reduction in the risk of developing diabetes when such people were treated with lifestyle interventions including nutritional management, weight loss and exercise (see Figure 4.5). More recently, a study has demonstrated the relationship between adherence to a 'Mediterranean' diet and reduced risk of future diabetes (Martinez-Gonzalez, de la Fuente-Arrillaga and Nunez-Cordoba 2008). The case for drug therapy is more controversial.

Study year

Subjects AT Risk Total no. Cumulative no. with diabetes: Intervention group Control group

Study year

Subjects AT Risk Total no. Cumulative no. with diabetes: Intervention group Control group

Figure 4.5 Improved risk of developing diabetes in the Finnish Diabetes Prevention Study, which involved a lifestyle intervention. Reproduced with permission from Tuomilehto J, Lindstrom J, Eriksson JG, et al. N Engl J Med 2001:344:1343-50.

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