Asthma incidence after age 6 years by gender and atopic status in the childhood allergy study

Background: Asthma is more prevalent in males before adolescence, yet more common among adult women. Later-onset asthma is often perceived to be less associated with atopy. We explored gender-specific asthma incidence in a birth cohort, stratifying by atopic status.

Method:  We used data from the Detroit Childhood Allergy Study to analyze the role of atopy during the period of apparent transition from male to female asthma predominance (i.e. between age 6 and 20).  Self or parental report of physician-diagnosed asthma was used to define incident asthma.  Atopy was defined as a specific IgE ≥ 0.35 for at least 1 of 7 common allergens.  A log-rank test was performed to determine the association of time to asthma among atopic and non-atopic males and females. A Cox regression analysis was done with the male, non-atopic group as the reference group. 

Results:  Of the 565 subjects included, 53% were female and 47% male. Females overall developed asthma after age 6 at a rate 1.73 times higher than males, hazard ratio (HR)=1.73 (1.04, 2.85), p=0.033.  The proportion of atopy among asthmatic females was 69% versus 70% among asthmatic males.  Atopic females were more than twice as likely to develop asthma compared to non-atopic females, HR=2.27 (1.21, 4.27); p=0.011. 

Conclusion:  Between the ages of 6 and 20 years, females developed asthma at a higher rate than males and associated atopy was common among new onset asthma in females. In young adults atopic asthma was equally prevalent in males and females and more than twice as common as non-atopic asthma.