|Wong, William -|
|Taylor, Addison -|
|Smith, E -|
|Barnes, Stephen -|
|Hachey, David -|
Submitted to: American Journal of Clinical Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 22, 2012
Publication Date: June 1, 2012
Citation: Wong, W.W., Taylor, A.A., Smith, E.O., Barnes, S., Hachey, D.L. 2012. Effect of soy isoflavone supplementation on nitric oxide metabolism and blood pressure in menopausal women. American Journal of Clinical Nutrition. 95(6):1487-1494. Interpretive Summary: Risk of high blood pressure increases quickly as women age, and soy intake is thought to help protect against high blood pressure. Isoflavones or phytoestrogens, found in high amounts in soy, are believed to increase nitric oxide production, a small compound known to relax blood vessels, thus lowering blood pressure and increasing blood flow. To evaluate this theory, we tested the effect of soy isoflavone supplementation on nitric oxide production and blood pressure in 24 menopausal women with high blood pressure. Half of these women took 80 mg of soy isoflavones per day for six weeks and the other half took a pill containing no isoflavones each day also for six weeks. We measured the nitric oxide production rate, blood pressure, and blood flow in these women before they started taking any of the pills and six weeks later. The soy isoflavones were found to have no effect on nitric oxide production, blood pressure, and blood flow.
Technical Abstract: Isoflavones, having chemical structures similar to estrogens, are believed to stimulate nitric oxide production and thus lower blood pressure. The efficacy of soy isoflavone supplementation to stimulate nitric oxide production and lower blood pressure in menopausal women with high normal blood pressure remains unknown. The objective was to test the effect of soy isoflavone supplementation on nitric oxide production and blood pressure in menopausal women with high normal blood pressure. A randomized, double-blind, parallel, placebo-controlled 6-wk trial was conducted to assess the effects of daily supplementation with 80 mg soy hypocotyl isoflavones (in aglycone units) on nitric oxide metabolism and blood pressure in 24 menopausal women with 12 women per group. Changes in nitric oxide metabolism were assessed via a primed, constant-infusion protocol with [(15)N]arginine and [(13)C]- and [(2)H]citrulline. Changes in blood pressure and associated vascular hemodynamics were assessed via office and 24-h ambulatory blood pressure monitoring, forearm blood flow, and indexes of arterial compliance. When compared with placebo and after control for pretreatment values, soy isoflavone supplementation had no effect on arginine flux, citrulline flux, nitric oxide synthesis, blood pressure, forearm blood flow, or estimates of arterial stiffness. Daily supplementation with 80 mg soy hypocotyl isoflavones over a 6-wk period had no effect on nitric oxide metabolism or blood pressure and associated vascular hemodynamics in menopausal women with high normal blood pressure.