Modification of Asthma With Soy Isoflavone

Asthma is a complex disease whose prevalence and severity are determined by multiple genetic
and environmental factors. The prevalence of asthma has increased during the past few
decades. Although causal relationships have not been proven, changing dietary practices
have paralleled the increase in asthma prevalence. Several surveys have found an
association between reduced lung function and decreased consumption of antioxidants,
flavonoids, and essential vitamins in a variety of respiratory conditions including asthma.
These findings suggest that diet may be a factor that impacts asthma and its clinical
manifestations.

Higher dietary consumption of soy isoflavones is associated with decreased self-report of
cough and other allergic respiratory symptoms. Our group reported an inverse relationship
between dietary intake of the soy isoflavone genistein and asthma severity. In addition, we
recently demonstrated that genistein inhibits synthesis of cysteinyl-leukotrienes in
eosinophils by blocking p38-dependent activation of 5-lipoxygenase, providing a plausible
cellular mechanism for the benefit of soy isoflavones in asthma. We also documented that
dietary soy isoflavone supplementation in asthma patients inhibited eosinophil
cysteinyl-leukotriene synthesis and decreased exhaled nitric oxide, an indicator of
eosinophilic airway inflammation. Our overall long-term goal is to translate these
epidemiological and mechanistic findings to human disease and determine whether dietary soy
isoflavones have a clinical role in asthma. We propose a clinical study powered to detect
an improvement in lung function as the first stop in achieving this goal.

Our hypothesis is that dietary supplementation with isoflavones will improve lung function,
reduce symptoms, and decrease airway inflammation in asthma. To test this, we will conduct
a randomized placebo-controlled, cross-over study of soy isoflavone supplementation in
patients with persistent asthma.