J Asthma. 2017 Apr;54(3):239-249. doi: 10.1080/02770903.2016.1206564. Epub 2016 Jul 6.
Association of living in a farming environment with asthma incidence in Canadian children.
Parsons MA1, Beach J2, Senthilselvan A1.
a School of Public Health, University of Alberta , Edmonton , Alberta , Canada.
b Division of Preventive Medicine, Department of Medicine, University of Alberta , Edmonton , Alberta , Canada.
The objective of this population-based 14-year follow-up study was to examine the effect of living in a farm environment on asthma incidence in children.
A total of 10,941 children of ages 0 to 11 years who were free of asthma and wheeze at the baseline (1994-1995) in the National Longitudinal Survey of Children and Youth were considered in the study. Children's living environment was classified, based on interviewer's observation, into three categories: non-rural, rural non-farming, and farming. An incidence of asthma was obtained from health-professional diagnosed asthma reported either by the person most knowledgeable for children under 15 years or by the children themselves if they were of ages 16 years and over.
The 14-year cumulative incidence of asthma among children living in farming environments was 10.18%, which was significantly lower than that observed for children living in rural non-farming (13.12%) and non-rural environments (16.50%). After adjusting for age group, number of older siblings, allergy, parental history of asthma, dwelling in need of repairs and SES index, a dose-response relationship was observed with children living in rural non-farming and farming environments having significantly reduced risk of asthma [hazard ratio (HR): 0.77; 95% confidence interval (CI): (0.60, 1.00); p = 0.047 and HR: 0.56; 95% CI: (0.41,0.77); p < 0.001] in comparison to those living in non-rural environments.
This cohort study provides further evidence that living in a farming environment during childhood is protective of asthma incidence in adolescence and adulthood and this finding provides further support for the hygiene hypothesis.