Soybean Compound Improves Vascular Function in Stroke Patients

By Todd Neale
HONG KONG, 29 sept 2008 -- Endothelial function in ischemic stroke patients can be significantly improved by supplementation with a compound found in soybeans, a randomized placebo-controlled trial showed.
After 12 weeks, patients who had been taking once-daily oral isoflavone had significantly greater flow-mediated dilation of the brachial artery compared with those who had been taking placebo (P=0.035), Hung-Fat Tse, M.D., Ph.D., of the University of Hong Kong's Queen Mary Hospital, and colleagues reported online in the European Heart Journal.
"These findings may have important implications for the use of isoflavone for secondary prevention in patients with cardiovascular disease, on top of conventional interventions," the researchers said.
However, Dr. Tse said, patients should not start supplementing their diets with the compound or eating more foods rich with isoflavone on the basis of the results.
"At this juncture," he said, "regular isoflavone supplementation might not be advocated since the benefits and side effects of long-term supplementation are still unknown."
In addition, the researchers said, the treatment effect was comparable to that achieved through endurance training or statin therapy.
Dr. Tse and colleagues previously showed improved vascular endothelial function with isoflavone supplementation in patients at high risk for cardiovascular disease, but it remained unknown whether patients with established cardiovascular disease would derive the same benefits.
So they randomized 50 patients who had suffered a first or recurrent ischemic stroke more than six months previously to 80 mg of isoflavone daily and 52 to placebo for 12 weeks.
Overall, the mean age of the patients was 66, and 66% were men. Nine percent had had a recurrent stroke, 10% had coronary artery disease, and 47% had diabetes.
Fasting brachial flow-mediated dilation was measured using ultrasound at baseline and at 12 weeks. The dilation was induced by inflating and releasing a pneumatic tourniquet on the patients' forearms.
A flow-mediated dilation value of 3.7% or lower was considered impaired. The vast majority of the patients (80%) had impaired function at baseline and there were no significant differences between the groups.
By the end of the study, flow-mediated dilation was 1% better in the treatment group than in the placebo group (P=0.035).
In addition, the prevalence of impaired flow-mediated dilation was significantly lower in the treatment group (58% versus 79%, P=0.023).
After adjusting for baseline flow-mediated dilation, isoflavone supplementation was associated with a 68% reduction in the prevalence of endothelial impairment (OR 0.32, 95% CI 0.13 to 0.80, P=0.014).
The effect was greatest in patients with more severe endothelial dysfunction at baseline (P<0.001).
"The findings suggest that isoflavone exerts a secondary vascular protective effect in patients with established atherosclerosis, despite a lack of effect on conventional cardiovascular risk factors including blood pressure, lipid profile, and blood glucose," the researchers said.
Isoflavone supplementation also caused a significant 1.7 mg/dL decrease in high-sensitivity C-reactive protein (P=0.033), which might partly explain the improvement in endothelial function, the researchers said.
Other possible mechanisms include direct action on vasorelaxation, modulation of platelet function, and antioxidant and hypocholesterolemic effects, although the results suggested the latter two explanations do not apply, they said.
In addition, they said, isoflavone is a type of phytoestrogen and its function as a partial estrogen agonist may explain the cardiovascular benefits.
The researchers noted that the treatment effect of isoflavone supplementation may have been underestimated because background isoflavone consumption is higher in Asian populations than in those consuming western diets.
The study was funded by CRCG small project funding from the University of Hong Kong, the Sun Chieh Yeh Heart Foundation, an Outstanding Young Investigator Award from the University of Hong Kong, and an unconditional research donation from Great Liaison Limited in Hong Kong.
The authors did not declare any conflicts of interest.
Primary source: European Heart JournalSource reference:Chan Y-H, et al "Reduction of C-reactive protein with isoflavone supplement reverses endothelial dysfunction in patients with ischemic stroke" Eur Heart J 2008; DOI: 10.1093/eurheartj/ehn409.