IGF-I is an important growth factor associated with increased colorectal cancer risk in epidemiological and experimental studies. Isoflavone intake has been associated with decreased cancer risk. Several studies have examined the effects of soy isoflavones on serum IGF-I levels, with inconsistent results. The purpose of this study is to evaluate the effects of an isolated red clover isoflavones supplement on the circulating IGF-system in women with an increased risk of colorectal cancer.

We conducted a randomized, placebo-controlled cross-over trial on the effects of red clover isoflavones supplementation (80 mg/day, two months) in postmenopausal women (n=35) with a history of colorectal adenomas or a family history of colorectal cancer.

Mean IGF-I and IGFBP-3 concentrations after placebo were 123.9 ± 38.9 μg/L and 2.01 ± 0.29 mg/L respectively. Isoflavone supplementation did not significantly alter serum total IGF-I concentrations (mean relative (%) within-person difference: -3%; 95%CI: -9% - 3%), nor the serum levels of IGFBP-3 (-2%; -5% - 1%). Results will also be presented for IGF-II, IGFBP-1, and IGFBP-2. Further analyses will take into account compliance (serum genistein), isoflavone metabolism (serum equol), and hormonal effects (serum estradiol, SHBG).

In conclusion, this study shows that two months isoflavones supplementation did not markedly affect the serum IGF-I and IGFBP-3 in a high risk population for colorectal cancer.

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA