Worldwide there has been a steady increase in the incidence of type 1 diabetes, with an average increase per year of 2.5-3.0%. This trend has been most clear in children under the age of four, and it has been highly irregular between different individual countries. Incidence of diabetes between European countries, for example, can vary up to ten-fold. The lowest incidences in the world are found in Venezuela and China, while the highest levels of diabetes are found in Finland and Sardinia. This overall increase in diabetes incidence are attributed to manifestation of the disease at an earlier age, and not an increase in the patients who get the disease in later life.
In a previous report by Dr Valma Harjutsalo, National Public Health Institute, Helsinki, Finland, and colleagues looked into trends in the disease between 1965 and 1996: they found a steady increase in the incidence of type 1 diabetes in Finland. They also predicted how many children would have it there in the future.
In this study, published by the same lead author, the research team explored three Finnish registers between the years 1980 and 2005: the National Public Health Institute Diabetes register, the Central Drug Register and the Hospital Discharge Register. They excluded several types of patients, including those with type 2 diabetes, and with diabetes in occurrence due to another condition, such as steroid use, Down's syndrome, or a physical abnormality of the pancreas.
Between 1980 and 2005, 10,737 children (5,816 boys and 4,921 girls) were diagnosed with type 1 diabetes before 15 years of age. In 1980 there were 31.4 cases per 100,000 while in 2005 there were 64.2 per 100,000 children, indicating that incidence almost doubled in this time period. This trend was most pronounced in children between birth and four years old, with an average increase of 4.7% per year. Differences were also seen between males and females: at the age of one, the cases were evenly distributed 1 boy to 1 girl, at the age of 13 years, this ratio was 1.7 boys to 1 girl. Additionally, the peak incidence for girls was at 10 years of age, while for boys it occurred three years later at the age of 13.
The resulting projected cumulative number of new cases of type 1 diabetes before 15 years of age between 2006 and 2020 is around 10,800. Finland has already exceeded its predicted levels of incidence by 2000 cases.
The authors attribute this increased onset in type 1 diabetes to many factors that include genetics and environmental triggers. Some risk factors include high birthweight or early weight gain in infancy: accordingly, levels of obese and overweight children in Finland have increased in the past twenty and especially in the past ten years, and the proportion of obese children between 5 and 15 years rose from 9.5% in the mid 1980's to 20% in 2008. A corresponding fall in birthweight accentuates this dramatic increase in obesity. Namely, these environmental influences could be affecting the penetrance of genes that are already present in the population.
Should levels of type 1 diabetes rise, the authors point out, the number of patients with serious diabetic complications will also increase considerably. These symptoms might include diabetic nephropathy. In conclusion, they emphasize the enormity of this trend in Finland: "The incidence of type 1 diabetes continues to increase sharply in Finland, where it has been documented to be the highest in the world since the 1950s. Evidence does not support the theory that the increase results only from a younger age at onset of the disease. The steep increase in incidence noted in the last half of the 1990s might represent a serious signal about unhealthy changes in our everyday environment that affect the penetrance of type I diabetes susceptibility genes."
Dr Mark Myers, Monash University Melbourne, Australia and Professor Paul Zimmet, Monash University Melbourne and International Diabetes Institute, Melbourne, contributed an accompanying comment in which they entertain the various possible causative effects of type 1 diabetes from exposure to different agents in the womb. "The case for an environmental contribution to the cause of type 1 diabetes is compelling. However, identification of probable agents is the ultimate challenge because they might be ubiquitous, and the hardest cause of a disease to identify is that which is universally present. There seems little doubt that we have underestimated the complexity of this form of diabetes" new ideas are clearly needed to stop the disconcerting acceleration of incidence.
Time trends in the incidence of type 1 diabetes in Finnish children: a cohort study
Valma Harjutsalo, Lena Sjoberg, Jaakko Tuomilehto
The Lancet, Vol 371, May 24, 2008
Halting the accelerating epidemic of type 1 diabetes
Mark Myers, Paul Zimmet
The Lancet, Vol 371, May 24, 2008
Written by Anna Sophia McKenney