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Soy supplement shows no blood pressure benefit

NEW YORK (Reuters Health) – Soy-rich diets have been linked to lower rates of heart disease, but a small study suggests that soy supplements may not do anything for older women’s blood pressure.

The findings, reported in the June issue of the American Journal of Clinical Nutrition, add to the mixed evidence on the health benefits of soy isoflavones.

Researchers have long known that Asian populations with soy-rich diets have lower rates of heart disease compared with people on Western diets. But it has not been clear whether soy isoflavone supplements have cardiovascular benefits.

A number of studies have found that intravenous infusions of soy isoflavones may boost the body’s production of nitric oxide and help blood vessels dilate. “But we don’t take soy by infusion,” said William Wong of Baylor College of Medicine in Houston who led the new study.

On top of that, he told Reuters Health, those earlier studies looked at short-term effects on blood vessel function — and not whether there are sustained benefits for blood pressure.

So for their study, Wong and his colleagues randomly assigned 24 menopausal women to take either soy isoflavones or placebo tablets for six weeks. The supplement gave a daily dose of 80 mg of isoflavones.

All of the women started the study with moderately elevated blood pressure. After six weeks, women on the soy supplement were faring no better than those on the placebo.

On average, systolic blood pressure was 136 mm/Hg in the placebo group, and 137 mm/Hg in the soy group. As for diastolic blood pressure, the average in both groups landed at about 80 mm/Hg.

Wong’s team also found no effect of the soy supplement on the women’s production of nitric oxide.

“It was disappointing,” Wong said.

The study only lasted for six weeks. But according to Wong, that should have been long enough to detect blood pressure benefits if there are any. “If we didn’t see anything in six weeks, we doubt there would be effects (longer term),” Wong said.

“I think that if people are looking for a magic bullet against high blood pressure,” he added, “this is not it.”

Netherlands-based Pharma Consulting and Industries BV provided the soy supplement Wong’s team used. The study was funded by the U.S. National Institutes of Health.


Am J Clin Nutr 2012.