The effect of soy isoflavones on arterial stiffness: a systematic review and meta-analysis of randomized controlled trials

Systematic review and meta-analysis of 8 randomized controlled trials in adults, including postmenopausal women and men. Participants ranged from healthy individuals to adults with metabolic syndrome or cardiovascular risk factors, and studies were conducted in multiple countries.

Included trials tested soy isoflavones in tablets, soy protein isolate, soy drink, soy nuts, or S-equol, with doses ranging from 10 mg to 118 mg aglycone equivalents daily. Regimens were generally compared with placebo or control over short intervention periods.

Soy isoflavone supplementation reduced arterial stiffness versus placebo in this meta-analysis of 8 randomized trials. Individual studies showed improvement in systemic arterial compliance in Nestel 1997 (p=0.011), augmentation index in Reverri 2015 (p=0.03), and pulse wave velocity in equol producers in Hazim 2016 (-0.2 ± 0.2 m/s vs 0.6 ± 0.2 m/s; p<0.01). Richter 2017 found no significant treatment effect on augmentation index (p=0.59) or PWV (p=0.84). The overall effect did not differ by intervention duration or gender.

The evidence base was small, with only 8 trials and modest individual sample sizes. Interventions were short, and the included studies used different soy formulations, populations, and arterial stiffness endpoints, which limits precision and generalizability. Several outcomes in the excerpt lacked study-specific numerical detail.