Urban vs rural residency and allergy prevalence among adult women: Iowa Women's Health Study.

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.