Effect of soy isoflavone supplementation on blood pressure: a meta-analysis of randomized controlled trials

This was a meta-analysis of randomized controlled trials in adults. Participants were mostly middle-aged to older women, with baseline ages ranging from 44 to 74 years, and included healthy individuals as well as patients with type 2 diabetes, metabolic syndrome, insulin resistance, or non-alcoholic fatty liver disease.

Soy isoflavone supplementation alone was evaluated versus placebo across 24 randomized controlled trials. Doses ranged from 40 to 300 mg/day, with intervention durations from 1 to 24 months (median 6 months); the review focused on mixed-type soy isoflavones rather than soy protein or other soy components.

Soy isoflavone supplementation produced a small but statistically significant reduction in blood pressure. Pooled effects favored soy isoflavones for systolic blood pressure (WMD, -1.40 mmHg; 95% CI, -2.62 to -0.14 mmHg) and diastolic blood pressure (WMD, -1.11 mmHg; 95% CI, -1.91 to -0.30 mmHg). Benefits appeared more pronounced with interventions lasting at least 6 months, with mixed-type isoflavones, and in healthy participants as well as those with metabolic syndrome or prehypertension. No clear dose-response relationship was identified.

The blood-pressure reduction was modest, and the evidence was drawn from trials with variable doses, durations, and participant populations. Most studies enrolled women, limiting generalizability to men, and the review did not identify a clear dose-response relationship. Reporting of some trial details, including frequency, route, and adverse events, was limited in the source packet.