To examine risk of type 1 diabetes mellitus (T1DM) in the offspring of parents with a psychiatric history at the birth of the child, which would suggest potential shared familial or environmental risk factors between T1DM and psychiatric disorders.

We established a cohort including all children born in Sweden in 1997–2016, and their parents. Children were followed up from birth until 31 Dec 2017, using national registers. Relative risk for T1DM was estimated by incidence rate ratios (RR) with 95% confidence intervals (CI), calculated from Poisson regression. We examined psychiatric subtypes, T1DM risk within subgroups and in relation to the timing of exposure.

The study cohort included 1,497,949 children. During follow-up, 7,794 cases of T1DM were identified. Children of mothers with psychiatric disorders at delivery had a higher risk of T1DM (RR 1.10 [95%CI 1.01–1.20]). Psychiatric diagnoses in fathers or assigned after delivery was not associated with increased T1DM risk. The observed association disappeared after adjusting for T1DM in parents; however, remained significant in female offspring. Maternal eating disorder (RR 1.53 [1.17–2.00]) and obsessive-compulsive disorder (RR 1.62 [1.02–2.58]) were associated with offspring T1DM, independent of parental T1DM.

Our results do not support a strong genetic link between psychiatric conditions and T1DM. However, the risks of offspring T1DM were increased in subgroups of female offspring and in offspring of mothers with a history of eating disorder or obsessive-compulsive disorder, independent of heredity for T1DM, which may warrant further investigation in future studies.