The aim of this study was to investigate the evidence of an increased risk of childhood-onset type 1 diabetes in children born by Caesarean section by systematically reviewing the published literature and performing a meta-analysis with adjustment for recognised confounders.

Aims/hypothesis Against a background of a near-universally increasing incidence of childhood type 1 diabetes, recent reports from some countries suggest a slowing in this increase. Occasional reports also describe cyclical variations in incidence, with periodicities of between 4 and 6 years. Methods Age/sex-standardised incidence rates for the 0- to 14-year-old age group are reported for 26 European centres (representing 22 countries) that have registered newly diagnosed individuals in geographically defined regions for up to 25 years during the period 1989–2013. Poisson regression was used to estimate rates of increase and test for cyclical patterns. Joinpoint regression software was used to fit segmented log-linear relationships to incidence trends. Results Significant increases in incidence were noted in all but two small centres, with a maximum rate of increase of 6.6% per annum in a Polish centre. Several centres in high-incidence countries showed reducing rates of increase in more recent years. Despite this, a pooled analysis across all centres revealed a 3.4% (95% CI 2.8%, 3.9%) per annum increase in incidence rate, although there was some suggestion of a reduced rate of increase in the 2004–2008 period. Rates of increase were similar in boys and girls in the 0- to 4-year-old age group (3.7% and 3.7% per annum, respectively) and in the 5- to 9-year-old age group (3.4% and 3.7% per annum, respectively), but were higher in boys than girls in the 10- to 14-year-old age group (3.3% and 2.6% per annum, respectively). Significant 4 year periodicity was detected in four centres, with three centres showing that the most recent peak in fitted rates occurred in 2012. Conclusions/interpretation Despite reductions in the rate of increase in some high-risk countries, the pooled estimate across centres continues to show a 3.4% increase per annum in incidence rate, suggesting a doubling in incidence rate within approximately 20 years in Europe. Although four centres showed support for a cyclical pattern of incidence with a 4 year periodicity, no plausible explanation for this can be given.

Globally, symptomatic type 1 diabetes (T1D) prevalence varies markedly. The International Diabetes Federation 11thEdition Atlas/T1D Index Version 3.0 estimated 2025 numbers for 202 countries/territories ("countries"), and projected to2040. The T1D Index model, a Markov model with sub-models for incidence-over-time, adult incidence, and mortality-over-time, was updated with recent population-based T1D incidence, mortality and prevalence studies. For countries without studies, data were extrapolated from countries with similarsettings. There are estimated 9.5 million people living with T1D globally (compared to 8.4 million in 2021, a 13 % increase), with 1.0 million of these aged 0-14, and 0.8 million aged 15-19 years. In lower-income countries, prevalent cases increased by 20 % from 1.8 million in 2021 to 2.1 million in 2025. Incident cases in 2025 are an estimated 513,000 (164,000 aged 0-14 and 58,000 aged 15-19 years), with incidence increasing by 2.4 % in the last year. Premature deaths are estimated at 174,000, with 17.2 % of these due to non-diagnosis soon after clinical onset. The estimated remaining life expectancy of a 10-year-old child diagnosed with T1D in 2025 varies between countries from 6 to 66 years. There are still no data available for 119 countries. The projectedT1D population for 2040 is estimated to be14.7 million. The number of global T1D cases is rising quickly, especially in lower-income settings, due to increasing diagnosed incidence, falling mortality and ageing, and population growth. Contemporary data are unavailable for over 50% of all countries, highlighting need for epidemiological studies.