Effects of soy isoflavone extract supplements on blood pressure in adult humans: systematic review and meta-analysis of randomized placebo-controlled trials.
OBJECTIVE
Reported effects of different soy products on blood pressure vary. This systematic review and meta-analysis was performed to clarify the effects of soy isoflavone extract supplements on systolic and diastolic blood pressure (SBP and DBP) in adult humans.


METHODS
PubMed, CENTRAL, ICHUSHI, and CNKI were searched in June 2009 for relevant randomized placebo-controlled trials. Study data and indicators of methodological validity were independently extracted by two authors using predefined data fields. Meta-analysis was carried out in Review Manager 5.0.22.


RESULTS
Searches identified 3740 articles, of which 14 randomized controlled trials (789 participants) were included. Daily ingestion of 25-375 mg soy isoflavones (aglycone equivalents) for 2-24 weeks significantly decreased SBP by 1.92 mmHg (95% confidence interval -3.45 to -0.39; P = 0.01) compared with placebo (heterogeneity P = 0.39, fixed effect model) in adults with normal blood pressure and prehypertension. The effect was not lost on sensitivity analysis. Subgroup analyses suggest greater effects in studies longer than 3 months, in Western populations, at lower doses, and in studies at lower risk of bias. Soy isoflavones did not affect DBP [-0.13 (95% confidence interval -1.03 to 0.78) mmHg, P = 0.78; heterogeneity P = 0.20, fixed effect model].


CONCLUSIONS
Soy isoflavone extracts significantly decreased SBP but not DBP in adult humans, and no dose-response relationship was observed. Further studies are needed to address factors related to the observed effects of soy isoflavones on SBP and to verify the effect in hypertensive patients.
Taku
Kyoko
K
Information Center, National Institute of Health and Nutrition, Tokyo, Japan. takuk@nih.go.jp
Lin
Ning
N
Cai
Donglian
D
Hu
Jianwei
J
Zhao
Xiaohui
X
Zhang
Yumei
Y
Wang
Peiyu
P
Melby
Melissa K
MK
Hooper
Lee
L
Kurzer
Mindy S
MS
Mizuno
Shoichi
S
Ishimi
Yoshiko
Y
Watanabe
Shaw
S
D001794:Blood Pressure / Q000187:drug effects*; D003971:Diastole / Q000187:drug effects; D019587:Dietary Supplements; D006801:Humans; D007529:Isoflavones / Q000494:pharmacology*; D010936:Plant Extracts / Q000494:pharmacology*; D016032:Randomized Controlled Trials as Topic; D013025:Glycine max; D013599:Systole / Q000187:drug effects
D007529:Isoflavones; D010936:Plant Extracts