Lack of association between month of birth and risk of developing type 1 diabetes in Brazil: a 40-year analysis

Abstract

Abstract Objectives Seasonal environment at birth may influence diabetes incidence in later life. We sought evidence for this effect and analyzed the association between the month of birth and the risk of developing type 1 diabetes mellitus (T1DM). Methods This was a cohort study carried out with 814 patients diagnosed with T1DM in the region of Bauru – São Paulo State, Brazil, receiving medical care in a private Endocrinology clinic or in the public Brazilian National Health Care System, from 1981 to 2021. All live births that occurred in São Paulo State between 1974 and 2020 were classified by month of birth and were considered as the control group. Results We found no statistically significant difference (χ2=16.31, critical 19.68) between the month of birth and risk of developing T1DM, when comparing our patients with the background population of the region. There was no association between the month of birth, sex, age at diagnosis, duration of symptoms before diagnosis, self-reported color, and socioeconomic status. Conclusions We found no association between month of birth and the risk of developing T1DM in this highly admixed South American population. Our data suggest that our population heterogeneity and geographic location may be important factors in the development of T1DM. Future prospective studies, evaluating environmental factors that may confer risk or protection to the disease, are warranted.