Could Soy Supplements Improve Asthma Outcomes?

Supplementation with soy isoflavones does not result in improved lung function or outcomes in adolescents and adults with poorly controlled asthma, according to new research.

While previous studies have suggested that soy isoflavone supplements may be helpful in treating a number of chronic diseases, including asthma, data on their efficacy is limited.

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In order to further explore whether these supplements could be used to improve asthma outcomes, researchers conducted a multicenter, randomized, double-blind, placebo-controlled trial between May 2010 and August 2012. The trial included 386 participants with poorly controlled asthma who were taking controller medication and had low dietary soy intake. After 24 weeks, 345 participants completed spirometry.

The participants were randomly assigned to receive either soy isoflavone supplements (100 mg) or placebo, taken daily for 24 weeks. Plasma genistein levels were used to measure the level of absorption in participants taking the supplement.

Overall, there was no significant difference in forced expiratory volume, symptoms, quality of life scores, number of asthma episodes, or systemic inflammation between the 2 groups.

“Among adults and children aged 12 years or older with poorly controlled asthma while taking a controller medication, use of a soy isoflavone supplement, compared with placebo, did not result in improved lung function or clinical outcomes. These findings suggest that this supplement should not be used for patients with poorly controlled asthma,” they concluded.

—Michael Potts

Smith LJ, Kalhan R, Wise RA, et al. Effect of a soy isoflavone supplement on lung function and clinical outcomes in patients with poorly controlled asthma. JAMA. 2015;313(20):2033-2043.