Our analysis compared the quantitative findings of all available epidemiological studies and shows that abdominal obesity, identified through a variety of measures, significantly raises the risk of type 2 diabetes across a range of different ethnic groups. Although adjustment factors varied, all the cohorts were adjusted for age and eight were adjusted for BMI, which we did not consider to be a measure of abdominal obesity. This gives us added confidence in the overall conclusion that, on average, raised abdominal obesity increases the risk of type 2 diabetes more than twofold.
When we commenced our work there was no comprehensive review examining the relationship between measures of abdominal obesity and the incidence of type 2 diabetes. When our work was completed a review addressing this issue albeit using different methods has been published, finding similar over all results to our own (14
). Our study adds independent confirmation of the findings of that study, but in addition provides statistical comparison between WC and other methods of measurement used in the studies, which is not undertaken directly by Vazquez et al. (14
No heterogeneity in the predictive value of different measures of abdominal obesity was identified. This suggests that WC (the most straightforward measure of abdominal obesity used in the studies) may be sufficient to identify subjects at raised risk. A similar finding has recently been reported in relation to the risk of cardiovascular disease (CVD); Koning et al. (15
) found that a 1 cm increase in WC is associated with a 2% increase in the relative risk of future CVD, and the difference between WC and WHR in terms of strength of association is not significant.
Different measures may capture different elements of abdominal obesity. WC cannot distinguish abdominal subcutaneous fat, total abdominal fat and total body fat, and it is strongly correlated with BMI (14
), although it performed at least as well as the other measures evaluated here. WC, or more usually maximal abdominal circumference, is easily measured and can be monitored by patients themselves. What this study demonstrates is that whatever measure is used they all show a strong relationship to the incidence of type 2 diabetes. This finding is important because it confirms that clinicians can use a simple measure of abdominal obesity in everyday practice to help identify patients at increased risk of developing type 2 diabetes.
The link between abdominal obesity and diabetes is biologically plausible. Abdominal fat is thought to increase the risk of diabetes through a number of secreted factors including non-esterified fatty acids and adipocytokines including tumour necrosis factor-α and reduced adiponectin. Reduction in WC is associated with an improvement in the circulating levels of these adipose tissue secreted factors. Thus, reducing WC may lead to a lower risk of progression to diabetes, as has been demonstrated in some studies targeting obesity and lifestyle in those at risk of type 2 diabetes (16
As the searches for our review were undertaken, a long-term follow up of multinational monitoring of trends and determinants in cardiovascular disease (MONICA) subjects examining the risk of the development of type 2 diabetes has been published (18
). This large study also identified no difference between WC and WHR in predicting risk, and provides further confirmation for our findings.
As a growing array of therapies offers the potential for significant reductions in obesity, effective targeting of these therapies towards those at higher risk and with the most to benefit from treatment may be improved by the systematic measurement of WC alongside other risk factors.