Background: The association between residence and allergy has been well studied in children living on a farm; however, studies of this association in late adulthood are lacking.
Objective: This study examined the association between residence and allergy in 25,393 women aged 55–69 years in the large prospective Iowa Women’s Health Study (IWHS).
Methods: IWHS questionnaires collected information on socio-demographic and anthropometric characteristics, medical history, lifestyle behaviors, dietary intake, residence and allergy. Residence reported at baseline (1986) was categorized into 5 groups based on living on a farm, rural, or urban areas and population size. Allergy was determined from four self-reported questions about physician-diagnosed asthma, hay fever, skin allergy, and other allergy. Logistic regression was used to determine significant risk factors for allergy and prevalence odds ratios (OR) and 95% confidence intervals (CI) for allergy associated with residence.
Results: Compared to large city of >10,000 residents, those living on farm, rural and smaller urban areas had decreased odds ratios of overall, skin, and other allergy in age and multivariable-adjusted models. The multivariable ORs (95% CI) for farm versus large city were decreased for overall allergy: 0.72 (0.66, 0.78) and all allergy types including asthma: 0.87 (0.75, 1.00), hay fever: 0.77 (0.69, 0.88), skin: 0.76 (0.68, 0.86), and other allergy: 0.76 (0.68, 0.86).
Conclusion: This study supports a hypothesis that farm living is inversely associated with allergy, suggesting that environmental exposures may protect against allergy not only in childhood, but also in late adulthood.