Incidence of type 2 diabetes in two Indigenous Australian populations: a 6-year follow-up study

Objective: To estimate the incidence of type 2 diabetes in two ethnically distinct Indigenous populations in north Queensland, Australia. Design, setting and participants: A community-based follow-up study of 1814 Australian Aboriginal and Torres Strait Islander adults from 1999 to 2007. Participants were initially free of diabetes and lived in 19 remote communities in Far North Queensland. Main outcome measures: Fasting blood glucose level; diagnosis of diabetes; blood lipid levels; weight; waist circumference (WC); and blood pressure. Results: Of the 554 adults who completed the study, 100 developed diabetes over 3412 person-years (py) of follow-up. The incidence of diabetes was similar for Aboriginals (29.7 [95% Cl, 20.4-38.4] per 1000 py) and Torres Strait Islanders (29.0 [95% Cl, 21.8-38.6] per 1000 py) despite large differences in baseline body mass index (BMI) and WC. The age-standardised incidence for both populations was 30.5 per 1000 py. Obesity defined by WC increased the risk of developing diabetes for Aboriginals (rate ratio [RR], 2.0 [95% Cl, 1.1-3.6]) and for Torres Strait Islanders (RR, 6.3 [95% Cl, 2.5-16.1]) compared with normal WC. Presence of the metabolic syndrome (MetS) was a strong predictor of incident diabetes (adjusted hazard ratio, 2.4 [95% Cl, 1.6-3.7]). For both groups, waist-to-hip ratio and the presence of the MetS better predicted diabetes than WC or BMI. Conclusions: The incidence of diabetes in these Indigenous Australians is nearly four times higher than for the non-Indigenous population and 50% higher than the incidence reported 10 years ago in Australian Aboriginals. Currently used BMI cut-off points are not appropriate for Indigenous Australians to predict diabetes.