The association between preschoolers' retinal microcirculation and the indoor microbial environment: results of the ENVIRONAGE birth cohort.

Early life environmental microbiota may influence normative development. Here, we explore the associations between the residential indoor microbial environment and the retinal microcirculation among preschoolers. We included 177 children aged 4-6 years from the Belgian ENVIRONAGE birth cohort. We measured retina microcirculation using fundus photography and quantified the retinal vessel tortuosity [tortuosity index (TI)] and diameters [central retinal vein equivalent (CRVE) and central retinal artery equivalent (CRAE)]. Residential indoor microbial characteristics (bacterial and fungal loads, richness, diversity, and taxa) were measured in settled dust using qPCR and amplicon sequencing. Adjusted associations were obtained using linear regression models and expressed as coefficients (β) with 95% confidence intervals (CI). We observed inverse associations between microbial loads and retinal microcirculation, significant for CRAE: β = -0.28; CI:-0.53;-0.04 (bacteria) and β = -0.27; CI:-0.50,-0.03 (fungi). Conversely, retinal microcirculation was directly associated with Gram-positive bacterial loads, significant for TI (β = 0.44; CI:0.06,0.81). These associations were stronger among boys. No consistent associations were observed for diversity. Conclusively, indoor microbial loads can affect the retinal microcirculation in preschool children. Retinal vascularization is a cardiovascular marker linked to immune factors and brain vascularization. Our findings support previously observed associations of the environmental microbiome with cognition, and open new hypotheses about potential cardiovascular effects.