Does insulin-like growth factor I predict incidence and progression of diabetic retinopathy?

We evaluated the relationship of insulin-like growth factor (IGF)-I to incidence and progression of diabetic retinopathy over a 6-year interval in a large population-based study of diabetes in southern Wisconsin. Participants included people with younger-onset diabetes (n = 66 adolescents, n = 661 adults > or = 18 years of age) and older-onset diabetes (n = 285 for those using insulin, n = 248 for those not using insulin). Fundus photographs were graded in a masked fashion using standardized protocols to determine the severity of retinopathy in each eye. Serum IGF-I levels were measured during 1984-1986 using a double-antibody radioimmunoassay. Mean IGF-I was highest in adolescents (499.1 micrograms/l), lower in younger-onset adult (280.1 micrograms/l), and lowest in the older-onset group (205.7 and 221.2 micrograms/l for older-onset group using insulin and not using insulin, respectively). The incidence of retinopathy was not significantly higher in people with higher IGF-I levels in any group. The odds of developing diabetic retinopathy in 6 years for each 10 micrograms/l increase in IGF-I after controlling for age, glycosylated hemoglobin, and duration of diabetes at baseline was 1.21 (95% confidence interval [CI] 0.95-1.54) for adolescents; 1.00 (95% CI 0.93-1.08) for younger-onset adults; 0.93 (95% CI 0.85-1.02) for the older-onset group using insulin; and 0.99 (95% CI 0.95-1.04) for the older-onset group not using insulin. In summary, IGF-I was not associated with 6-year incidence or progression of diabetic retinopathy in any of the groups.