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Vascular Sciences Research Group, Monash University Department of Medicine, Dandenong Hospital, Melbourne (H.J.T., D.G., F.S.D., B.P.M.)
Jean Hailes Research Group, Monash Institute Health Services Research, Clayton (H.J.T.)
Victoria, University of Western Australia, School of Medicine and Pharmacology, Perth, Western Australia (J.H.), AUSTRALIA
Address reprint requests to: Address correspondence to: Prof. Helena Teede, Jean Hailes Research Group, Monash Institute of Health Services Research, Level 1 Block E, Monash Medical Centre, 246 Clayton Road, Clayton 3168, Melbourne, AUSTRALIA. E-mail: helena.teede{at}med.monash.edu.au
Objective: To examine the effects of dietary soy/isoflavones on 24 hr blood pressure profiles and arterial function [systemic arterial compliance (SAC), pulse wave velocity (PWV) and brachial arterial flow mediated vasodilation (FMD)] compared to non legume-based plant protein without isoflavones, in hypertensive subjects.
Design: In a 6 month double-blind, placebo controlled, cross-over trial, 41 hypertensive subjects (26 men, 15 postmenopausal women), 30–75 years, received soy cereal (40 g soy protein, 118 mg isoflavones) and gluten placebo cereal, each for 3 months.
Results: Thirty-eight subjects completed protocol with results expressed as mean or mean change (±SEM) with each intervention. Soy increased urinary isoflavones (daidzein: 8-fold; genistein: 8-fold; equol: 9-fold; ODMA: 18-fold) with no change during gluten placebo. There was no difference in the change in individual 24 hr ambulatory BP parameters (SBP: 2 ± 2 vs –1 ± 1 mmHg, p = 0.21; DBP: 1 ± 1 vs –1 ± 1 mmHg, p = 0.06) central BP (cSBP: –4 ± 2 vs 0 ± 2 mmHg, p = 0.2) or the change in arterial function (FMD: 0.3 ± 0.5 vs –0.2 ± 0.5%, p = NS; SAC: 0.02 ± 0.02 vs –0.02 ± 0.02 U/mmHg, p = NS; PWV central: –0.2 ± 0.2 vs 0.0 ± 0.2 m/sec, p = NS; PWV peripheral: 0.01 ± 0.3 vs –0.4 ± 0.4 m/sec, p = NS) noted between interventions. Analysis of the area under curve of 24 hr BP outputs demonstrated that soy protein compared to gluten protein resulted in higher 24 hr systolic BP by 2.3 mmHg (p = 0.003), a higher daytime systolic BP by 3.4 mmHg (p = 0.0002) and a higher daytime diastolic BP by 1.4 mmHg (p = 0.008). Overall 24 hr diastolic BP, night systolic BP and night diastolic BP were not significantly different between groups. Furthermore, soy protein compared to gluten protein resulted in higher 24 hr heart rates by 3.5 bpm (p < 0.0001).
Conclusions: In hypertensive subjects, compared to gluten placebo, soy dietary supplementation containing isoflavones had no effect on arterial function, on average 24 hr ambulatory blood pressure parameters or central blood pressure in men and women with hypertension. Area under the curve of 24 hr profiles demonstrated that daytime BP was higher after soy compared to gluten.
Key words: endothelial function, pulse wave velocity, arterial stiffness, soy protein, gluten, ambulatory blood pressure
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  G. E. Mann, D. J. Rowlands, F. Y.L. Li, P. de Winter, and R. C.M. Siow Activation of endothelial nitric oxide synthase by dietary isoflavones: Role of NO in Nrf2-mediated antioxidant gene expression Cardiovasc Res, July 15, 2007; 75(2): 261 - 274. [Abstract] [Full Text] [PDF]
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