Interaction between glycaemic control and serum insulin-like growth factor 1 on the risk of retinopathy in type 2 diabetes

Background There is strong experimental evidence that insulin-like growth factor 1 (IGF-1) plays a role in the development of diabetic retinopathy. We carried out this study to determine the association between serum IGF-1 levels and retinopathy in patients with type 2 diabetes and whether this association is modified by the severity of hyperglycaemia. Materials and methods A total of 480 consenting patients with type 2 diabetes were enrolled between 1 August 2001 and 31 December 2002. All participants provided a medical history and underwent a physical examination, biochemical assessment and eye fundi examination. These patients were followed up in our clinics according to our national guidelines until 31 December 2009. Results Compared with the middle tertile, increased levels of IGF-1 did not increase the risk of mild-to-moderate retinopathy (RR, 1.11; 95% CI, 0.631.95) and severe retinopathy (RR, 1.84; 95% CI, 0.798.57) at baseline. In the longitudinal analysis, increased levels of IGF-1 showed a nonsignificantly increased hazard ratio (HR) for the progression of retinopathy (HR, 1.61; 95% CI, 0.524.96) and severe retinopathy (HR, 1.63; 95% CI, 0.654.09). However, in patients with relatively good glycaemic control, there was a significantly increased risk of the progression of retinopathy (HR, 2.21; 95% CI, 1.015.91) and a cumulative incidence of severe retinopathy (HR, 4.82; 95% CI, 1.1018.25) in individuals with the highest serum IGF-1 levels. Conclusions Our data suggested serum IGF-1 was a contributing factor in severe diabetic retinopathy and this effect may be masked by poor glycaemic control.