Effect of soy protein and isoflavones on blood pressure and endothelial cytokines: a 6-month randomized controlled trial among postmenopausal women

Background: Despite data from animal models and observational studies that are generally supportive for the soy/isoflavones lowering blood pressure (BP) and improving vascular function, the current findings from clinical trials are still inconclusive. Objectives: To examine whether soy protein with isoflavones or isoflavones alone reduce BP and endothelial cytokines, and whether the effects differed by baseline BP level. Methods: A double-blind randomized, placebo-controlled trial was conducted among 180 postmenopausal Chinese women with mild hyperglycemia. Participants were randomly assigned to one of the three arms to receive either 15 g soy protein and 100 mg isoflavones (Soy group), or 15 g milk protein and 100 mg isoflavones (Iso group), or 15 g milk protein (placebo group) on a daily basis for 6 months. Results: No significant difference was observed in the change and % change of BP and endothelial cytokine levels among the three study groups. However, a subgroup analysis among 130 pre and hypertensive women suggested that soy protein and isoflavones significantly reduced SBP [-4.25%, 95% confidence interval (CI) -7.9 to -0.6%, P = 0.02] and the level of soluble intercellular adhesion molecule (sICAM)-1 (-22.6%, 95% CI -42.8 to -2.3%, P = 0.02) relative to milk protein after 6-month intervention. Conclusions: Our 6-month randomized controlled trial in prediabetic postmenopausal women indicated that soy protein and isoflavones had no significant effect on BP and endothelial molecules; however, a favorable reduction on SBP, sICAM-1 and E-selectin was observed among women with initial elevated BP.