Siblings and risk of allergic rhinitis: a systematic review and meta-analysis

Abstract

Following the “hygiene hypothesis”, a plethora of studies have investigated the role of sibship composition in atopic diseases, but findings are largely conflicting. We undertook the first systematic review to synthesize the global literature linking birth order and sibship size to the risk of allergic rhinitis. Fifteen databases were searched from inception until 20 October 2021. Screening and data extraction were performed in pairs. Comparable numerical data were analyzed using meta-analysis with robust variance estimation (RVE). We included 76 reports based on 66 studies that met our inclusion criteria, encompassing >2 million subjects. Being second- or later-born child was associated with protection against both current (pooled risk ratio [RR] 0.79, 95%CI 0.73-0.86) and ever (RR 0.77, 95%CI 0.68-0.88) allergic rhinitis. Having siblings, regardless of birth order, was associated with a decreased risk of current allergic rhinitis (RR 0.89, 95% CI 0.83-0.95) and allergic rhinoconjunctivitis (RR 0.92, 95%CI 0.86-0.98). These effects were unchanged across age, time period, and geographical regions. Our findings indicate that primarily, a higher birth order, and to a lesser extent the number of siblings, is associated with a lower risk of developing allergic rhinitis.

Global burden of pediatric asthma and rhinitis – what we have recently learned from epidemiology

“…In children with current allergic rhinitis, birth order >2 versus 1 was associated with 21% lower risk and number of siblings >2 versus 1 with 11% lower risk of AR. Being the second or subsequent sibling in the family was associated with protection for current AR [relative risk (RR) 0.79, 95% CI 0.73–0.86] and ever AR (RR 0.77, 95% CI 0.68–0.88) [28].…”