The headline:
Children are more likely to develop diabetes in winter, newspapers have reported. The Times said that a large international study of 31,000 children from 53 countries suggests there is a correlation between the seasons and type 1 diabetes. It said the trend was more prevalent in boys and older children (5-14 year olds) of both sexes.
The news stories are based on a large, well-conducted time series study that demonstrates a seasonal variation in the diagnoses of type 1 diabetes across the world. The researchers conclude that the seasonality “is a real phenomenon”, but that more data are needed on populations living in the southern hemisphere, such as southern Africa, Australia and South America “to complete the picture”. There are no explanations that account for the differences seen between girls and boys and the differences in the age groups
NHS Choices says that:
The results from this large, well conducted study confirm what has been seen in previous small studies. However, any interpretation of these findings should take into account several shortcomings that the researchers themselves raise:
- Most of the centres that participated in the WHO DiaMond study were situated in the northern hemisphere. There is very limited information available for Africa and Asia and the researchers say that the correlation is far from conclusive.
- The link between new cases and the seasons was influenced by the total number of cases diagnosed in a centre. The researchers suggest that this might be because a larger number of cases gives the study more power to find an association if it exists. If this is the case, it may also explain why seasonality was more evident in the older age groups (which usually have more people with diabetes) than the youngest one. However, they also say it is possible that an as yet unidentified factor could be behind the association.
- The researchers make several suggestions explaining a seasonal variation for type 1 diabetes, including children getting more exercise in the summer, more infections in the winter and seasonal variations in their levels of blood glucose. However, none of these fully explains the differences seen in age groups and across the genders.
Although the study was well conducted and efforts were made to standardise the data from the different centres, it is possible that there were differences in diagnostic practice or reporting between the centres that may have biased the results. As an ecological design, the study looked at the effect of seasons on the incidence of diabetes in a population group, such as a clinic or country. This means that there are no definite implications for individuals. The study’s value is in generating theories of how diabetes may be caused and in pointing future investigation in a particular direction, rather than showing that season is a definite factor.
Overall, the researchers conclude that the seasonality of type 1 diabetes “is a real phenomenon”, but that more data are needed on populations living below the 30th parallel (for example southern Africa, Australia and South America) “to complete the picture”.
Links to the headlines:
Diabetes 'most likely to occur among children in winter'. The Times, August
24 2009
Children 'more likely to develop diabetes in winter than in summer'. The Daily Telegraph, August 24 2009
Risk of diabetes 'rises in winter'. The Metro, August 24 2009
Links to the science:
Moltchanova EV, Schreier N, Lammi N and Karvonen M. Seasonal variation of diagnosis of Type 1 diabetes mellitus in children worldwide. Diabetic Medicine 2009; 26: 673-678
