Soy isoflavone supplementation elevates erythrocyte superoxide dismutase, but not plasma ceruloplasmin in postmenopausal breast cancer survivors

Soy isoflavone antioxidant effects may help prevent breast cancer re-occurrence, but isoflavone estrogen-like actions may increase breast cancer risk. These isoflavone actions can be reflected by effects on two copper enzymes activities, superoxide dismutase 1 (SOD 1), which has antioxidant function relevant to breast cancer prevention, and ceruloplasmin, which has its synthesis up-regulated by estrogen, and for which high values are associated with high breast cancer risk. A soy isoflavone-rich concentrate supplement was examined for effects on these two copper enzyme activities in post-menopausal breast cancer survivors (n = 7) in a crossover design with a placebo (24 days on supplement or placebo; 14 day wash out). The soy concentrate, but not the placebo, increased erythrocyte SOD 1 activities, but not ceruloplasmin activities or protein. The effect on superoxide dismutase activities was not likely due to increased copper intake since analysis of the soy extract showed little copper. The effect on superoxide dismutase was not accompanied by a change in urinary contents of 8-deoxyhydroxyguanosine, a DNA oxidant product, though perhaps this would change with a longer intervention. In summary, in regard to two copper enzyme activities, an isoflavone-rich soy concentrate showed an antioxidant effect considered relevant to breast cancer, but not an effect associated with estrogenic activity and increased breast cancer risk.