K. G. M. M. Alberti

A cluster of risk factors for cardiovascular disease and type 2 diabetes mellitus, which occur together more often than by chance alone, have become known as the metabolic syndrome. The risk factors include raised blood pressure, dyslipidemia (raised triglycerides and lowered high-density lipoprotein cholesterol), raised fasting glucose, and central obesity. Various diagnostic criteria have been proposed by different organizations over the past decade. Most recently, these have come from the International Diabetes Federation and the American Heart Association/National Heart, Lung, and Blood Institute. The main difference concerns the measure for central obesity, with this being an obligatory component in the International Diabetes Federation definition, lower than in the American Heart Association/National Heart, Lung, and Blood Institute criteria, and ethnic specific. The present article represents the outcome of a meeting between several major organizations in an attempt to unify criteria. It was agreed that there should not be an obligatory component, but that waist measurement would continue to be a useful preliminary screening tool. Three abnormal findings out of 5 would qualify a person for the metabolic syndrome. A single set of cut points would be used for all components except waist circumference, for which further work is required. In the interim, national or regional cut points for waist circumference can be used.

To define the type of dietary fibre of fibre analogue with the greatest potential use in diabetic treatment, groups of four to six volunteers underwent 50-g glucose tolerance tests (GTT) with and without the addition of either guar, pectin, gum tragacanth, methylcellulose, wheat bran, or cholestyramine equivalent to 12 g fibre. The addition of each substance significantly reduced blood glucose concentration at one or more points during the GTT and generally reduced serum insulin concentrations. The greatest flattening of the glucose response was seen with guar, but this effect was abolished when hydrolysed non-viscous guar was used. The reduction in the mean peak rise in blood glucose concentration for each substance correlated positively with its viscosity (r = 0.926; P less than 0.01), as did delay in mouth-to-caecum transit time (r = 0.885; P less than 0.02). Viscous types of dietary fibre are therefore most likely to be therapeutically useful in modifying postprandial hyperglycaemia.

A workshop was convened by the International Diabetes Federation to review the latest information relating to the risks associated with impaired glucose tolerance (IGT) and impaired fasting glycaemia (IFG) for future diabetes and cardiovascular disease (CVD). The workshop sought to address three questions: (i) are the current definitions of IGT and IFG appropriate; (ii) are IFG and IGT risk factors, risk markers or diseases; (iii) what interventions (if any) should be recommended for people with IFG and IGT? The determinants of elevated fasting glucose and 2-h plasma glucose in an oral glucose tolerance test (2-HPG) levels differ. Raised hepatic glucose output and a defect in early insulin secretion are characteristic of the former, and peripheral insulin resistance is most characteristic of the latter. Therefore, it is not surprising that the concordance between the categories of IFG and IGT is limited. In all prevalence studies to date only half or less of people with IFG have IGT, and even a lower proportion (20-30%) with IGT also have IFG. In the majority of populations studied, IGT is more prevalent than IFG, and there is a difference in phenotype and gender distribution between the two categories. IFG is substantially more common amongst men and IGT slightly more common amongst women. The prevalence of IFG tends to plateau in middle age whereas the prevalence of IGT rises into old age. Both IFG and IGT are associated with a substantially increased risk of developing diabetes, with the highest risk in people with combined IFG and IGT. Because IGT is commoner than IFG in most populations it is more sensitive (but slightly less specific) for identifying people who will develop diabetes. In most populations studied, 60% of people who develop diabetes have either IGT or IFG 5 years or so before, with the other 40% having normal glucose tolerance at that time. The limited published data suggest that both isolated IFG (I-IFG) and isolated IGT (I-IGT) are similarly associated with cardiovascular risk factors, such as hypertension and dyslipidaemia, with the highest risk in those with combined IFG and IGT. However, some data have suggested that I-IGT is more strongly associated with hypertension and dyslipidaemia (features of the metabolic syndrome) than I-IFG. In unadjusted analyses both IFG and IGT are associated with CVD and total mortality. In separate analyses for fasting and 2-HPG adjusted for other cardiovascular risk factors (from the DECODE study) there remains a continuous relationship between 2-HPG and mortality, but an independent relationship with fasting glucose is only found above 7.0 mmol/l. Glycated haemoglobin (HbA1c) levels are continuously and positively associated with CVD and total mortality independent of other CVD risk factors. Life style interventions, including weight loss and increased physical activity, are highly effective in preventing or delaying the onset of diabetes in people with IGT. Two randomized controlled trials of individuals with IGT found that life style intervention studies reduce the risk of progressing to diabetes by 58%. The oral hypoglycaemic drugs metformin and acarbose have also been shown to be effective, but less so than the life style measures. Similar data do not yet exist for the effectiveness of such interventions in people with I-IFG. Larger studies are required to evaluate the effects of interventions on cardiovascular outcomes in people with IGT. Cost effective strategies to identify people with IGT for intervention should be developed and evaluated. The use of simple risk scores to assess who should undergo an oral glucose tolerance test is one promising approach, although these will need to be population-specific. In conclusion, IGT and IFG differ in their prevalence, population distribution, phenotype, and risk of total mortality and CVD. The consensus of the workshop was: 1. The diagnostic thresholds for all categories of glucose intolerance should be revisited in the light of the latest evidence. There was no clear consensus (with current evidence) on whether IFG and IGT should be classified as diseases, but they clearly represent risk factors and risk markers for diabetes and CVD, respectively. 2. Both IGT and IFG are similarly associated with an increased risk of diabetes, but IGT is more strongly associated with CVD outcomes. 3. Risks are higher when IGT and IFG coexist. 4. Life style interventions are highly effective in delaying or preventing the onset of diabetes in people with IGT and may reduce CVD and total mortality, but the latter requires formal testing.