Exposure to isoflavone-containing soy products and endothelial function: A Bayesian meta-analysis of randomized controlled trials

Beavers, D.P.; Beavers, K.M.; Miller, M.; Stamey, J.; Messina, M.J.

doi:10.1016/j.numecd.2010.05.007

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Exposure to isoflavone-containing soy products and endothelial function: A Bayesian meta-analysis of randomized controlled trials

D.P. Beavers
- Department of Biostatistical Sciences, Wake Forest University School of Medicine, Winston-Salem, NC, USA
- DP Beavers and KM Beavers contributed equally to this manuscript.
K.M. Beavers
- The Section on Gerontology and Geriatric Medicine, Wake Forest University School of Medicine, Winston-Salem, NC, USA
- Corresponding author at: J. Paul Sticht Center on Aging, Wake Forest University School of Medicine, Medical Center Boulevard, Winston-Salem, NC 27157, USA. Tel.: +1 336 713 8529; fax: +1 336 713 8588.
- DP Beavers and KM Beavers contributed equally to this manuscript.
M. Miller
- Department of Cardiology, University of Maryland School of Medicine, Baltimore, MD, USA
J. Stamey
- Department of Statistical Sciences, Baylor University, Waco TX, USA
M.J. Messina
- Nutrition Matters, Inc., Port Townsend, WA, USA

Received 20 January 2010; received in revised form 20 May 2010; accepted 24 May 2010. published online 16 August 2010.
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Abstract

Background and Aims

To determine whether and to what degree exposure to isoflavone-containing soy products affects EF. Endothelial dysfunction has been identified as an independent coronary heart disease risk factor and a strong predictor of long-term cardiovascular morbidity and mortality. Data on the effects of exposure to isoflavone-containing soy products on EF are conflicting.

Methods and Results

A comprehensive literature search was conducted using the PUBMED database (National Library of Medicine, Bethesda, MD) inclusively through August 21, 2009 on RCTs using the keywords: soy, isoflavone, phytoestrogen, EF, flow mediated vasodilation, and FMD. A Bayesian meta-analysis was conducted to provide a comprehensive account of the effect of isoflavone-containing soy products on EF, as measured by FMD. A total of 17 RCTs were selected as having sufficient data for study inclusion. The overall mean absolute change in FMD (95% Bayesian CI) for isoflavone-containing soy product interventions was 1.15% (−0.52, 2.75). When the effects of separate interventions were considered, the treatment effect for isolated isoflavones was 1.98% (0.07, 3.97) compared to 0.72% (−1.39, 2.90) for isoflavone-containing soy protein. The models were not improved when considering study-specific effects such as cuff measurement location, prescribed dietary modification, and impaired baseline FMD.

Conclusions

Cumulative evidence from the RCTs included in this meta-analysis indicates that exposure to soy isoflavones can modestly, but significantly, improve EF as measured by FMD. Therefore, exposure to isoflavone supplements may beneficially influence vascular health.

Keywords: Soy, Isoflavone, Endothelial function, Flow-mediated dilation, Meta-analysis

Abbreviations: CVD, cardiovascular disease, EF, endothelial function, FMD, flow-mediated dilation, NO, nitric oxide, RCT, randomized controlled trial, BAD, brachial artery diameter, SEM, standard error of the mean, SD, standard deviation, CI, confidence interval, ER, estrogen receptor