June 2013

Document Type


Degree Name



Oregon Health & Science University


There is mounting evidence that increased circulating levels of insulin-like growth factor I (IGF-I) are associated with an increased risk of prostate cancer (CaP). Green tea (GT) supplementation significantly reduces circulating IGF-I levels in CaP patients and IGF-I levels and tumor development in the murine TRAMP model of CaP. To determine if GT affects IGF-I levels in men prior to development of CaP, we conducted an analysis of blood samples from a randomized, double-blind, placebo-controlled trial entitled “Catechins and ω-3 fatty acids: impact on fatty acid synthase activity in the prostate. A randomized controlled trial.” Men scheduled for repeat prostate biopsy were recruited from three hospitals in Portland, OR, and randomized into one of four treatment arms: placebo(PP), fish oil (FO), GT, or GT/FO. Blood samples were drawn before and after a treatment period of 12-20 weeks. Pre and post-treatment plasma (n=71) and serum (n=3) IGF-I concentrations were determined using commercially available radioimmunoassay kits. There were no significant differences in IGF-I concentrations between the GT (n=13) and placebo groups (n=24) at baseline (p=0.46). Following treatment, IGF-I concentrations were significantly lowered in the GT supplemented group as compared to placebo (p=0.01, mean difference =-24.91, 95%CI -46.30, -3.52). These results were also confirmed with a non-parametric Wilcoxin Rank Sum test (p=0.017). When all four arms were analyzed for interaction using an orthogonal linear contrast, none was found between GT and FO(p=0.13, 2- tailed). In addition, there was no significant difference found between GT and GTFO groups at either pre or post-intervention. These findings suggest that GT supplementation lowered IGF-I and that this effect is independent of any effect of FO supplementation. Following this, we considered FO an additional placebo and found the overall main effect of GT remained significant when men supplemented with FO were added to the analyses (p=0.03, Wilcoxon rank-sum test). These findings suggest that GT polyphenols lower circulating IGF-I in pre-cancerous men which may, in turn, reduce CaP risk.




Graduate Programs in Human Nutrition


School of Medicine



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