The effect of soy isoflavone intake on cardiovascular disease risk factors - potential role of equol
Isoflavones, the subclass of flavonoids found in soybeans, may reduce the risk of cardiovascular disease (CVD). However, the current evidence is inconsistent. The capability to produce the isoflavone metabolite equol in 20-60 % of the population might underlie the benefits of isoflavone intake on vascular health. In a retrospective analysis of a 12-month intervention containing isoflavones (100 mg isoflavones, as aglycones equivalents), postmenopausal women with Type 2 diabetes who were equol producers (EPs) had significantly lower diastolic blood pressure (BP), mean arterial BP and arterial stiffness (assessed by pulse wave velocity (PWV)) (mean change from baseline ()±SEM; -2.2±1.3 mmHg, -1.2±1.3 mmHg, -0.7±0.4 m/s, respectively, P<0.01) than non-EPs. Subsequently, an acute crossover double-blind study was conducted where EP and non-EP males at elevated heart disease risk were prospectively recruited (n=14 per group) to determine whether EP phenotype was associated with differential vascular responses. The effects of an isoflavone supplement (80mg; single-dose) on endothelial function, PWV and BP were assessed at baseline, and at the anticipated Tmax for plasma isoflavones (6h) and equol (24h). After isoflavone intake, EPs had significantly decreased PWV at 24h (±SEM: isoflavone -0.2±0.2, placebo +0.6±0.2; P<0.01). However, isoflavone intake had no effect on the vascular measures at the 6h and 24h timepoints. To further investigate the acute vascular effects of S-equol per se, synthetic S-equol supplements (40 mg) were consumed by non-EPs at the anticipated Tmax for plasma S-equol (2h) and this showed no significant vascular benefits. In conclusion, acute isoflavone intake improved arterial stiffness in male EPs at increased CVD risk, with the magnitude of change potentially equating to a 10-12% risk reduction in risk of CVD if sustained. Synthetic equol intake had no acute benefit on vascular health in non-EPs. These data suggest that the EP phenotype may partly predict the effectiveness of soy isoflavones on arterial stiffness. Further long term RCTs with prospectively recruited EPs are required to confirm the importance of equol production for cardiovascular health.
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