Isoflavone intake in persons at high risk of cardiovascular events: implications for vascular endothelial function and the carotid atherosclerotic burden

Background: Epidemiologic studies have suggested that a high phytoestrogen intake is inversely associated with cardiovascular disease risk factors and the incidence of cardiovascular events. However, the relation between the intake of isoflavone, a major component of phytoestrogen, and vascular endothelial function and the atherosclerotic burden remains unclear. Objective: We aimed to investigate the effects of various dietary soy isoflavone intakes on brachial artery flow-mediated dilation and mean maximum carotid intima-media thickness. Design: We studied 126 consecutive patients ((x) over bar +/- SD age: 66.5 +/- 11.1 y: 69% male) at high risk of cardiovascular events (94% had documented coronary artery disease or stroke; 44% had diabetes). A validated food-frequency questionnaire was used to estimate their dietary intake after they achieved stable dietary patterns for 3 mo. Results: The median intakes of isoflavone and soy protein were 5.5 (range: 2.2-13.3) mg/d and 1.2 (range: 0.4-2.8) g/d, respectively. Persons in the 4th quartile of daily isoflavone intake had significantly (P < 0.05) greater flow-mediated dilation-but not mean maximum carotid intima-media thickness-than did those in the lower quartiles. After adjustment for potential confounders, a higher isoflavone intake in the 4th than in the 1st quartile (>13.3 mg/d), but not a higher intake of soy protein, predicted an absolute 2.71% increase in flow-mediated dilation (relative increase: 103%; P = 0.02) and a 0.17-mm decrease in mean maximum carotid intima-media thickness (relative decrease: 14.5%; P = 0.04). Conclusion: In persons at high risk of cardiovascular events, a greater isoflavone intake is associated with better vascular endothelial function and lower carotid atherosclerotic burden.