Insolation and Disease Severity in Paediatric Inflammatory Bowel Disease—A Multi-Centre Cross-Sectional Study

This study was to investigate whether the clinical course of inflammatory bowel disease (IBD) in a Polish paediatric cohort fits a seasonal pattern and depends on insolation. Two hundred and fourteen patients diagnosed with Crohn’s disease (CD) and 192 with ulcerative colitis (UC) aged from 3 to 18 years, were recruited in seven centres of similar latitude. The seasons were defined as winter (December–February), spring (March–May), summer (June–August), autumn (September–November). The year was also divided depending on insolation threshold (3.0 kWh/m(2)/day). Patients diagnosed with IBD when the isolation was >3 kWh/m(2)/day had poorer nutritional status than those diagnosed while insolation was below threshold (lower standardised BMI at diagnosis (−0.81 ([−1.34]–[−0.03]) vs. −0.52 ([−1.15]–0.15); p = 0.0320) and worst flare (−0.93 ([−1.37]–[−0.05]) vs. −0.66 ([−1.23]–0.17); p = 0.0344), with the need for more frequent biological treatment (45.5% vs. 32.7%, p = 0.0100). Patients diagnosed in winter were significantly younger at diagnosis (11.4 vs. 13.0; p(adj) = 0.0180) and first immunosuppressive treatment (11.3 vs. 13.3; p(adj) = 0.0109) than those diagnosed in other seasons. CD patients diagnosed in months with higher insolation spent more days in hospital than those diagnosed in months with lower insolation [4.6 (1.8–11.8) vs. 2.9 (1.3–6.2); p = 0.0482]. CD patients diagnosed in summer had significantly more concomitant diseases. In patients with CD, the occurrence of the worst flare was more frequent in autumn. Furthermore, the season of birth was associated with Pediatric Crohn’s Disease Activity Index at worst flare and earlier surgery. In conclusion, several clinical parameters are associated with insolation, the season of diagnosis and season of birth in the clinical course of Crohn’s disease.