Meta-analysis links asthma, passive smoking, and frequent snacks to recurrent respiratory infections in preschoolers

OBJECTIVE: This study aims to systematically retrieve observational studies on risk factors for recurrent respiratory tract infection (RRTI) in preschool children globally and perform a meta-analysis to comprehensively evaluate the effect sizes of major risk factors. METHODS: This study systematically searched databases including PubMed, Embase, Wiley Library, China National Knowledge Infrastructure (CNKI), Wanfang and VIP Chinese Journals Database (VIP) for relevant literature from inception to September 2025. The subjects included were preschool children, the outcome was the diagnosis or occurrence of RRTI and the study types were limited to observational studies. Evaluated indicators included household economic status, maternal age at childbirth, duration of breastfeeding (< 6 months), frequent snack intake (> 7 times/week), passive smoking, asthma and vitamin A deficiency. RESULTS: A total of 12 studies involving 170 915 children were included. Meta-analysis showed that asthma (OR = 3.26, 95% CI: 1.85-5.7), passive smoking (OR = 1.50, 95% CI: 1.20-1.87) and frequent snack intake (OR = 1.61, 95% CI: 1.35-1.92) were significant risk factors for RRTI in preschool children. Higher maternal age at childbirth (OR = 0.941, 95% CI: 0.913-0.97) showed a protective association. However, no statistically significant associations were found for household economic status (OR = 0.95, 95% CI: 0.82-1.10), breastfeeding for less than 6 months (OR = 1.24, 95% CI: 0.96-1.61) or vitamin A deficiency (OR = 1.42, 95% CI: 0.85-2.36). Sensitivity analyses indicated robust results for the main findings but publication bias could not be assessed due to the limited number of studies included in each meta-analysis. CONCLUSION: The occurrence of RRTI in preschool children is influenced by multiple factors. This study confirms that asthma, passive smoking and an unhealthy diet (frequent snack intake) are established risk factors, whilst older maternal age may be protective. For household economic status, breastfeeding duration and vitamin A levels, the current pooled evidence did not establish statistically significant associations with RRTI. Prevention strategies could therefore prioritise asthma management, avoidance of tobacco smoke and promotion of healthy eating to reduce the risk of RRTI.