Association between body mass index and diabetic retinopathy in Chinese patients with type 2 diabetes

To explore the factors mediating the relationship between body mass index (BMI) and diabetic retinopathy (DR) in Chinese type 2 diabetes patients.

This is a cross-sectional study. Data of 2,533 patients with type 2 diabetes were studied from the Shanghai Diabetes Registry Database. DR was assessed using non-mydriatic fundus photography and graded as non-DR, mild-moderate (DR I-II), and sight-threatening (DR III-IV). BMI (kg/m(2)) was classified as normal weight (18.5 ≤ BMI < 25), overweight (25 ≤ BMI < 30), and obese (BMI ≥ 30). β cell function was evaluated by fasting C-peptide (FCP).

DR was present in 701 (27.7 %) patients. Patients with DR had lower BMI (24.3 vs. 24.9 kg/m(2), P = 0.001) and fasting C-peptide (1.46 vs. 1.86 ng/ml, P < 0.001) than those without DR. The association between BMI (2 kg/m(2) interval) and DR was U-shaped; patients with BMI 28-29.9 kg/m(2) had the lowest DR rate. Compared with normal weight, overweight was associated with reduced risk of any DR [odds ratio (OR) 0.73], DR I-II (OR 0.76), and DR III-IV (OR 0.64) after adjustment for sex, age at diabetes diagnosis, and duration of diabetes. This negative association attenuated after adjustment for other confounders and became nonsignificant after further adjustment for FCP. Patients with different BMI categories had similar DR risk when stratified by FCP tertiles.

Overweight patients have lower DR prevalence than normal weight individuals, which may be attributable to better β cell function in overweight patients.