Roles of gender and smoking in the associations between urinary phytoestrogens and asthma/wheeze and lung function: evidence from a cross-sectional study.

BACKGROUND:The role of phytoestrogens in asthma/wheeze and lung function remains controversial. Thus, we aimed to examine whether phytoestrogens have beneficial effects on asthma/wheeze, lung function for subgroups and mortality. METHODS:Participants in this study were individuals aged 20 years or older from the National Health and Nutrition Examination Survey. Multivariate logistic regression models were fitted to examine the associations of urinary phytoestrogens with the risk of asthma/wheeze and lung function in individuals with and without asthma/wheeze. Cox proportional hazards regression was used to examine the relationship between urinary phytoestrogens and all-cause mortality. Stratified analyses were conducted based on gender and smoking status. RESULTS:We included 2465 individuals in this study. Enterolactone levels in the highest quartile were associated with a lower risk of asthma than those in the lowest quartile. As compared with the lowest quartile, the highest quartile of enterodiol and enterolactone was associated with a lower risk of wheeze. Significant associations were observed between subtypes of phytoestrogens (equol and enterolactone) and lung function (forced vital capacity (FVC) and forced expiratory volume in 1 s). Besides, FVC was higher in individuals with higher levels of enterodiol. The results were consistent in subpopulations without asthma/wheeze, while the significant difference was not observed in individuals with asthma/wheeze. The stratified analyses revealed that the associations between phytoestrogens and lung function differed by gender and smoking status among subgroups. No significant association was found between urinary phytoestrogens and all-cause mortality. CONCLUSION:In summary, subtypes of phytoestrogens were associated with lower risk of asthma/wheeze and beneficial for lung function improvement in individuals without asthma/wheeze. Furthermore, gender and smoking may interact in the relationship between phytoestrogens and asthma/wheeze, and lung function. Further researches are needed to confirm these associations and explain the results of stratified analyses.