Soya isoflavone-enriched cereal bars affect markers of endothelial function in postmenopausal women

Soya isoflavones are thought to be cardioprotective due to their structural similarity to oestrogen. In order to investigate the effect of soya isoflavones on markers of endothelial function we conducted a randomised, double-blind, placebo-controlled, cross-over study with thirty healthy postmenopausal women. The women consumed cereal bars, with or without soya isoflavones (50mg/d), for 8 weeks, separated by an 8-week washout period. Systemic arterial complince (SAC), isobaric arterial compliance (IAC), flow-mediated endothelium-dependent vasodilation (FMD) and nitroglycerine-mediated endothelium-independent vasodilation (NMD) were measured at the beginning of the study and after each intervention period. Blood pressure (BP) and plasma concentrations of nitrite and nitrate (NOx) and endothelin-1 (ET-1) were measured at the beginning and end of each intervention period.NMD was 13·4 (sem 2·0) % at baseline and 15·5 (sem 1·1) % after isoflavone treatment compared with 12·4 (sem 1·0) % after placebo treatment (P=0·03). NOx increased from 27·7 (sem 2·7) to 31·1 (sem 3·2) μm after isoflavones treatment compared with 25·4 (sem 1·5) to 20·4 (sem 1·1) μm after placebo treatment (P=0·003) and a significant increase in the NOx:ET-1 ratio (P=0·005) was observed after the isoflavone treatment compared with placebo. A significant difference in SAC after the isoflavone and placebo treatment was observed (P=0·04). No significant difference was found in FMD, IAC, BP and ET-1. In conclusion, 8 weeks' consumption of cereals bars enriched with 50mg soya isoflavones/d increased plasma NOx concentrations and improved endothelium-independent vasodilation in healthy postmenopausal women.