Background Coeliac disease (CD) incidence has increased in recent decades, characterised by variations according to sex, age at diagnosis, year of birth, month of birth and region of birth. Genetic susceptibility and exposure to gluten are the necessary factors in CD aetiology, although several environmental factors are considered.
Methods A nationwide prospective cohort longitudinal study was conducted consisting of 1 912 204 children aged 0–14.9 years born in Sweden from 1991 to 2009. A total of 6569 children were diagnosed with biopsy-verified CD from 47 paediatric departments. Using Cox regression, we examined the association between CD diagnosis and season of birth, region of birth and year of birth.
Results Overall, CD risk was higher for children born during spring, summer and autumn as compared with children born during winter: adjusted HR for spring 1.08 (95% CI 1.01 to 1.16), summer 1.10 (95% CI 1.03 to 1.18) and autumn 1.10 (95% CI 1.02 to 1.18). Increased CD risk was highest if born in the south, followed by central Sweden when compared with children born in northern Sweden. Children diagnosed at <2 years had an increased CD risk if born in spring while those diagnosed at 2–14.9 years the risk was increased for summer and autumn births. The birth cohort of 1991–1996 had increased CD risk if born during spring, for the 1997–2002 birth cohort the risk increased for summer and autumn births, while for the birth cohort of 2003–2009 the risk was increased if born during autumn.
Conclusions Season of birth and region of birth are independently and jointly associated with increased risk of developing CD during the first 15 years of life. Seasonal variation in infectious load is the likely explanation.
- General Paediatrics
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Contributors All authors contributed equally to the conceptualisation of the study, data collection, selection of the study variables, study design, interpretation of study findings and revision of the manuscript, and have approved the submitted versions of the manuscript. FN performed the statistical analyses and wrote the manuscript. ML supervised the analysis, ensured quality of data and the study results. AI and OS provided clinical insights and interpretation of the study variables and findings.
Funding The study was funded by the Swedish Research Council, through the SIMSAM programme [839-2008-7491] and by the Swedish coeliac disease association, funders played no other role.
Competing interests None declared.
Ethics approval Swedish research ethical review board.
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement All data used were obtained from Sweden’s national registers. These are open and data can be obtained upon request from Swedish data management agencies.