Written by Jessica Patella, ND. This review of 11 researches showed that those taking 65-153 mg of soy isoflavones per day for 1-12 months lowered blood pressure in people that had high blood pressure.
Approximately one billion people worldwide and 74.5 million Americans are affected by high blood pressure (1, 2). High blood pressure is a major risk factor for cardiovascular disease (2). Conversely, a 4-5 mmHg reduction in systolic blood pressure and a 2-3 mmHg reduction in diastolic blood pressure, can decrease the risk of cardiovascular disease by 8-20% (3).
Isoflavones are derived from soybeans and have antioxidant properties. Soy isoflavones have been shown to improve blood pressure, although the research has shown mixed results. A recent meta-analysis included eleven different research studies that examined the effect of soy isoflavones on blood pressure to get a better understanding of the effects (3). A meta-analysis includes a substantial amount of the available studies and takes into account the data from them and forms an overall conclusion.
When compared to placebo, supplementation with soy isoflavones (65-153 mg/day) resulted in an average decrease of 2.5 mmHg (p=0.08) in systolic blood pressure and a decrease of 1.5 mmHg (p=0.08) in diastolic blood pressure (3).
When the subjects were divided into a hypertensive group (high blood pressure; 5 trials) and a normotensive group (6 trials) the decrease in blood pressure was greater in the hypertensive population . The hypertensive group had an average decrease in systolic blood pressure of 5.94 mmHg (p=0.01) and a decrease in diastolic blood pressure of 3.35 mmHg (p=0.04) . There was no significant change in blood pressure seen in subjects that already had normal blood pressure (3).
The mechanism of how the soy isoflavones affect blood pressure is still not entirely understood. It is thought that isoflavones increase production of Nitric Oxide, which dilates blood vessels, and then results in lower blood pressure. This would explain why the blood pressure did not change in normotensive subjects, because the blood vessels already dilate properly.
In conclusion, the review of eleven studies show taking 65-153 mg of soy isoflavones per day for 1-12 months lowered blood pressure in subjects that had high blood pressure (3). Further research with larger groups and a controlled study need to be conducted to further understand how soy isoflavones decrease blood pressure.
Source: Liu, X. X., et al. “Effect of soy isoflavones on blood pressure: a meta-analysis of randomized controlled trials.” Nutrition, Metabolism and Cardiovascular Diseases 22.6 (2012): 463-470.
© 2010 Elsevier B.V. All rights reserved.
Posted March 02, 2011.
References:
- American Heart Association. High Blood Pressure Statistics. Chobanian AV, et al. Seventh report of the Joint National Committee on prevention, detection, evaluation, and treatment of high blood pressure. Hypertension 2003; 42:1206-52.
- Liu XX, et al. Effects soy isoflavones on blood pressure: A meta-analysis of randomized controlled trials. Nutr, Metab, Cardio Dis 2010; doi:10.1016/j.numecd.2010.09.006
