Seasonality of birth in patients with childhood type 1 diabetes in nineteen European regions

AIMS/HYPOTHESIS:
Differences in seasonality of birth patterns between the general population and the group who develop Type I (insulin-dependent) diabetes mellitus indicate that environmental factors operating around the antenatal and perinatal period could be important. We investigated whether the same unsual patterns in seasonality of birth observed in children with Type I diabetes in Great Britain could also be found in other European populations.
METHODS:
Population-based incidence cohorts of children diagnosed with Type I diabetes under 15 years of age from 1989 onwards were analysed. Previously reported data sets from Great Britain were also included together with data on children diagnosed over an additional 5 year period (1988-1992). To assess the role of seasonality in diabetes, we used the method of Walter and Elwood to examine monthly birth figures for each country or region.
RESULTS:
Outside of Great Britain, no seasonality of birth was seen for any single or combination of European countries. Significant sinusoidal patterns were observed in Scotland, Yorkshire and Leicester, although the peak for Leicester appeared around autumn rather than spring. There was little evidence that sex or age at diagnosis played a part in differences in seasonal patterns, either overall or for any individual country.
CONCLUSIONS/INTERPRETATION:
We found no uniform seasonal pattern of birth in childhood diabetes patients across European populations, either overall or according to sex and age. This study provides no consistent evidence that environmental factors, which vary from season to season, have any influence on the fetal or neonatal life to determine the onset of Type I diabetes. However, a study of seasonality that takes into account possible changes both over time and over geographical areas could provide more insights.