The review, published in Nutrition, Metabolism and Cardiovascular Diseases, demonstrated that consumption of between 65 and153 mg of soy isoflavones with soy protein per day, for 1–12 months, had an effect of lowering blood pressure in hypertensive (high blood pressure) populations by 5.9 mmHg.
“The magnitude of the decrease in blood pressure observed is comparable to that observed in response to antihypertensive agents, such as beta-blockers … Accordingly, our findings may have significant implications in reduction of CVD risk if applied to the hypertensive population,” said the reviewers, led by X. Liu, from Peking Union Medical College and Chinese Academy of Medical Sciences, China.
Hypertension is estimated to affect approximately one billion individuals worldwide, and is known to be a major risk factor in the development of cardiovascular disease (CVD).
In addition to pharmacological therapies, dietary interventions provide an important approach for preventing and treating hypertension, according to the American Heart Association.
Liu and colleagues noted that soy isoflavones have been suggested to result in the widening of blood vessels, improvement in artery function, and decreased blood pressure. However, they said that clinical trials in humans have shown inconsistent results.
As a result, the authors said that a meta-analysis of the available evidence may provide further insight into the potential benefits of soy isoflavone.
“We evaluated the effect of isoflavones on blood pressure through meta-analysis of all randomized, double-blind, and placebo-controlled clinical trials with a stated amount of soy protein,” said the authors.
Liu and co- workers identified 35 potentially relevant articles through an in depth search of all published literature. Of these 35 studies, eleven met the selection criteria for meta-analysis, and data from these trials on the effect of soy isoflavones on blood pressure was pooled.
In comparison to placebo, soy isoflavone treatment was shown to reduce systolic blood pressure by 2.5 mmHg and a decrease in diastolic blood pressure of 1.5 mmHg.
The reviewers then performed a subgroup analysis according to blood pressure status. Subjects were divided into two subcategories: hypertensive [high blood pressure] populations (5 trials) and normotensive [normal blood pressure] populations (6 trials).
“The results from these analyses showed that the reduction in blood pressure was greater in isoflavone-treated subjects than in placebo subjects in the hypertensive population … In contrast, no significant differences were observed in blood pressure between subjects treated with soy isoflavones or placebo in the normotensive individuals,” said the researchers.
Liu and colleagues said the mechanism of the blood pressure lowering effect of soy isoflavones in hypertensive subjects is not well understood. However they noted that previous research “provides a plausible explanation for this observation by showing that oral isoflavone supplementation leads to a significant improvement in endothelial function.”
They said that such a mechanism may be plausible as normotensive patients, who showed little benefit from soy isoflavone, generally have good endothelial function, whilst hypertensive patients often have associated endothelial dysfunction.
“Soy isoflavones may exhibit antihypertensive effects in hypertensive subjects due to restoration of endothelial function … However, this effect needs to be confirmed in large and carefully designed clinical trials with longer durations,” they said.
Source: Nutrition, Metabolism and Cardiovascular Diseases
Published online ahead of print, doi: 10.1016/j.numecd.2010.09.006
“Effect of soy isoflavones on blood pressure: A meta-analysis of randomized controlled trials”
Authors: X.X. Liu, S.H. Li, J.Z. Chen, K. Sun, X.J. Wang, X.G. Wang, R.T. Hui