Is insulinlike growth factor I associated with diabetic retinopathy?

Insulinlike growth factor I (IGF-I) is the mediator of the growth-promoting effects of growth hormone and has been suspected of playing a role in the pathogenesis of proliferative diabetic retinopathy (PDR). However, previous attempts to correlate IGF-I levels with PDR have yielded conflicting results. We determined IGF-I levels in a large population-based study of 682 early-onset (diagnosed before 30 yr of age) adult (greater than or equal to 18 yr old) insulin-taking diabetic subjects. PDR was found in 25% of the population. IGF-I levels were measured by radioimmunoassay. The mean serum level of IGF-I was 277 +/- 108 micrograms/L (mean +/- SD). Spearman rank correlations showed statistically significant negative correlations between IGF-I levels and age (r = -0.51, P less than 0.0001), duration of disease (r = -0.36, P less than 0.0001), and glycosylated hemoglobin (r = -0.09, P less than 0.05). There was a significant trend (P less than 0.001) toward decreasing risk of PDR with increasing IGF-I. However, after controlling for duration of diabetes, glycosylated hemoglobin, diastolic blood pressure, and the presence of proteinuria and/or creatinine greater than or equal to 265 microM in a multiple logistic regression model, IGF-I was not significantly associated with PDR. These data suggest that IGF-I may not be a risk factor for the development of PDR.