Effect of birth season on allergic rhinitis and cedar pollinosis considering allergen and vitamin D exposure: The Japan Environment and Children's study (JECS).

BACKGROUND: The relationship between the season of birth, allergen sensitization, and allergic rhinitis have been inconsistent, and there are no studies that simultaneously consider vitamin D and allergen exposure. This study aimed to determine the associations between the season of birth, house dust mite (HDM) and Japanese cedar pollen (JCP) sensitization, and allergic rhinitis and pollinosis, while taking vitamin D levels and allergen exposure into account.

METHODS: This study included 4323 participants in the Sub-Cohort Study of the Japan Environment and Children's Study. A logistic regression model was used to analyze the association between the season of birth and sensitization to JCP or HDM (judged by specific immunoglobulin E) at age 2 and allergic rhinitis or pollinosis at age 3, adjusted for HDM or JCP exposure and vitamin D levels with potential confounders.

RESULTS: Participants born in spring or summer were more likely to have pollinosis than were those born in winter (adjusted odds ratio [aOR]: 2.08, 95% confidence interval [CI]: 1.13-3.82 for spring; aOR: 1.89, 95% CI: 1.03-3.47 for summer). Participants born in summer were more likely to have HDM sensitization than were those born in winter (Der p 1, aOR: 1.53, 95% CI: 1.10-2.15; Der f 1, aOR: 1.44, 95% CI: 1.03-2.01). Exposure to JCP and HDM were associated with pollinosis and HDM sensitization, respectively.

CONCLUSIONS: Spring and summer births were associated with the development of pollinosis, and summer birth was associated with HDM sensitization, even when vitamin D and allergen exposure were considered. Further studies on mechanisms other than vitamin D and allergen exposure are required.