medwireNews: BMI has a strong positive linear association with type 2 diabetes risk that generally does not vary by global region or ethnicity, show results of a dose-response meta-analysis.
The study, published in The BMJ, also found similar associations for measures of central adiposity but not for hip circumference.
Sakineh Shab-Bidar (Tehran University of Medical Sciences, Iran) and colleagues analyzed data from 216 prospective (88%) and retrospective (12%) cohort studies with almost 26 million participants, including 2.3 million individuals with type 2 diabetes, that evaluated the association between general or central adiposity and body fat content and the type 2 diabetes risk in the general adult population.
They found that, overall, each 5-unit increase in BMI was associated with a significant 1.72-fold increased risk for type 2 diabetes (based on data from 182 studies), which persisted in subgroup analyses based on participant and study characteristics, as well as across all ethnicities and regions.
A non-linear dose-response meta-analysis of data from 122 studies showed that the association between BMI and diabetes risk was strongly linear and did not deviate from linearity at a specific cutoff value.
For waist circumference (n=78 studies), each 10 cm increase was associated with a significant 1.61-fold (n=78) increased risk for type 2 diabetes that was also strongly linear and persisted across subgroups.
In addition, there was a positive linear association for waist-to-hip ratio (n=34 studies) where each 0.1-unit increase was associated with a significant 1.63-fold increased diabetes risk, while there were positive monotonic associations for waist-to-height ratio (n=25 studies) and visceral adiposity index (n=9 studies).
Each 0.1-unit increase in waist-to-height ratio was associated with a significant 1.73-fold increased risk for diabetes and each 1.0-unit increase in visceral adiposity index was associated with a significant 2.05-fold increased risk.
Fewer studies measured percentage body fat (n=6), body shape index (n=5), and body adiposity index (n=4), but analysis of these showed significant positive associations with diabetes risk for all three measures.
Shab-Bidar et al note that in the analyses of central adiposity indices, the associations “became stronger after adjustment for body mass index, suggesting that deposition of fat in this area of the body, independent of overall fatness, was related to a higher risk.”
For hip circumference (n=14 studies), the researchers observed that the direction of the association depended on adjustment for waist circumference. Specifically, there was a significant negative association between hip circumference and diabetes risk in the studies that adjusted for waist circumference. Conversely, there was a significant positive association when waist circumference was not taken into account.
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