Effect of soy isoflavone supplementation on vascular endothelial function and oxidative stress in postmenopausal women: A community randomized controlled trial

A 12-month randomized double blind controlled trial was conducted among 182 Indonesian postmenopausal women aged 47 to 60 years to determine the effect of 100 mg/day soy isoflavone supplementation on vascular endothelial function such as vascular cell adhesion molecule-1 (VCAM-1), nitric oxide (NO) and malondialdehyde (MDA) as oxidative stress marker. The subjects were randomized to the intervention group receiving tablets consisting of 100 mg soy isoflavones and calcium carbonate 500 mg, and to the control group receiving 500 mg calcium carbonate. The concentrations of VCAM-1, NO and MDA were measured at baseline, and postsupplementation at 6 months and 12 months. After supplementation, the MDA concentrations were significantly lower in the soy isoflavone group compared with the control group (p=0.001). The concentrations of VCAM-1 and NO were not affected (p=0.992 and p=0.759, respectively). In all group the MDA concentration increased compared with baseline concentrations but the relative change of MDA concentrations was significantly lower in the soy isoflavone group compared with the control group. This study demonstrates that supplemental intake of soy isoflavones for 6 months and 12 months had an effect on oxidative stress by decreasing MDA concentration, but did not improve vascular endothelial function.