Comparison of body mass index at diagnosis of diabetes in a multi-ethnic population: a case-control study with matched non-diabetic controls

Aims: To investigate the probability of developing type 2 diabetes mellitus (T2DM) at different body mass index levels compared to matched non-diabetic controls in a multi-ethnic population. Materials and methods: This was a case-control study of 90 367 patients with incident diabetes and 362 548 age-sex-ethnicity matched controls from UK primary care. The probability of developing T2DM was estimated. Results: Case and control patients were 56 years old at index and 56% were male. Patients with T2DM had significantly higher mean BMI levels by about 5 kg/m² at diagnosis (32.2 kg/m²) compared to the matched controls (27.4 kg/m²). White Europeans (n = 79 270), African-Caribbeans (n = 4115) and South Asians (n = 7252) were 58, 48 and 46 years old with a mean BMI of 32.5, 31.1 and 29.2 kg/m², respectively, at diagnosis. More South Asians developed T2DM at BMI below 30 kg/m² (38%) than White Europeans (26%) and African-Caribbeans (29%) (all P <.01). Within the 18 to 70-year age range, South Asian males and females had a significantly higher probability of developing diabetes in the continuously measured BMI range of 18 to 30 kg/m², compared to White Europeans and African-Caribbeans. Across all age groups <70 years, South Asians and African-Caribbeans had a significantly higher probability of developing T2DM in the normal weight and overweight categories, compared to White Europeans. However, this risk pattern of developing diabetes was reversed amongst the obese in all age groups. Conclusion: Risk patterns of developing diabetes at different levels of obesity varies among ethnic groups across all ages, while South Asians and African-Caribbeans carry the highest risk at a younger age and at lower adiposity burden.