Isoflavonoids do not inhibit in vivo lipid peroxidation in subjects with high-normal blood pressure

The isoflavonoids genistein and daidzein have been shown to have antioxidan t activity in vitro, but their effects on in vivo oxidation have not been a ssessed. The newly described F-2-isoprostanes are believed to currently rep resent the best available marker of in vivo lipid peroxidation. Therefore w e have assessed the effects of a 55 mg daily isoflavonoid supplement on uri nary F-2-isoprostane concentrations in subjects with high-normal blood pres sure (BP). A total of 59 subjects completed an 8-week parallel design, rand omized, double blind, and placebo-controlled study. F-2-isoprostanes, isofl avonoids and creatinine were measured in 24-h urine samples taken at baseli ne and at the end of the intervention. There were significant increases in urinary excretion of genistein (5.22 +/- 0.75 mg/day, P < 0.0001) and daidz ein (2.53 +/- 0.43 mg/day, P < 0.0001) in the group taking the isoflavonoid supplement. Creatinine excretion was significantly correlated with F-2-iso prostanes at baseline (r = 0.45, P < 0.01). After adjustment for baseline v alues, there was no significant difference between groups in creatinine adj usted post-intervention F-2-isoprostane concentrations (P = 0.74). In addit ion, changes in genistein and daidzein excretion were not significantly cor related with changes in F-2-isoprostanes in the isoflavonoid treatment grou p. These results are not consistent with the suggestion that the two soy de rived isoflavonoids have in vivo antioxidant activity at a level of intake achievable: by dietary means and in subjects with high-normal BP. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.