Farming environments and childhood atopy, wheeze, lung function, and exhaled nitric oxide

BACKGROUND: Previous studies have demonstrated that children raised on farms are protected from asthma and allergies. It is unknown whether the farming effect is solely mediated by atopy or also affects nonatopic wheeze phenotypes. OBJECTIVE: We sought to study the farm effect on wheeze phenotypes and objective markers, such as lung function and exhaled nitric oxide, and their interrelation with atopy in children. METHODS: The GABRIEL Advanced Studies are cross-sectional, multiphase, population-based surveys of the farm effect on asthma and allergic disease in children aged 6 to 12 years. Detailed data on wheeze, farming exposure, and IgE levels were collected from a random sample of 8023 children stratified for farm exposure. Of those, another random subsample of 858 children was invited for spirometry, including bronchodilator tests and exhaled nitric oxide measurements. RESULTS: We found effects of exposure to farming environments on the prevalence and degree of atopy, on the prevalence of transient wheeze (adjusted odds ratio, 0.78; 95% CI, 0.64-0.96), and on the prevalence of current wheeze among nonatopic subjects (adjusted odds ratio, 0.45; 95% CI, 0.32-0.63). There was no farm effect on lung function and exhaled nitric oxide levels in the general study population. CONCLUSIONS: Children living on farms are protected against wheeze independently of atopy. This farm effect is not attributable to improved airway size and lung mechanics. These findings imply as yet unknown protective mechanisms. They might include alterations of immune response and susceptibility to triggers of wheeze, such as viral infections