The Study of Soy Isoflavones in Asthma

Asthma is a common disease that has a major impact on morbidity and health care costs. Although the prevalence and severity of asthma have increased over the last several decades, the specific causes remain unknown. One possible mechanism is a change in diet. Yet, epidemiological and interventional studies designed to identify a key nutrient or antioxidant vitamin that may be responsible for the increase in disease severity have produced inconsistent results. A recent pilot study showed a soy isoflavone supplement reduces exhaled nitric oxide (FeNO) and ex vivo LTC4 synthesis in patients with inadequately controlled asthma. This clinical trial is designed to test the novel hypothesis that dietary supplementation with soy isoflavones is an effective treatment in patients with poorly controlled asthma. The study will include 380 patients with low dietary soy intake, 12 years of age or older, who are taking either inhaled corticosteroids or leukotriene modifiers and have inadequately controlled asthma. Participants will be randomly assigned to treatment with either a soy isoflavone supplement (containing genistein, daidzein and glycitein; 100 mg daily of the glycoside forms) or placebo for six months. The results of this trial will increase understanding of the role of diet in asthma; could identify a novel, safe and relatively inexpensive treatment for patients with asthma; and potentially will have a substantial impact on public health in the United States.