ENVIRONMENTAL factors related to decreased early antigen exposure and maternal obesity could be behind the rising incidence of type 1 diabetes in many countries, researchers say.

Rates continue to climb at around 3% to 5% annually in many countries, but evolving genetic susceptibility does not fully explain increased incidence in genetically stable populations and among people who migrate from low- to high-incidence areas.

Findings from a US study of 1852 children aged less than 19 years with type 1 diabetes and 7408 controls showed improved hygiene and living conditions reduced antigen exposure early in life and increased the risk for diabetes.

Consistent with the hygiene hypothesis, the study found that lower socio-economic status and having older siblings reduced the risk of diabetes while having three or more siblings halved the risk.

The study also found that the risk of type 1 diabetes increased in children whose mother had either a body mass index of 30 or higher or weighed above 90kg before pregnancy.

The researchers said this finding supported the overload or “accelerator hypothesis” which posits that overload of pancreatic beta cells early in life makes them prone to autoimmunity and cell death.

Associate Professor Jonathan Shaw, associate director of the Baker IDI Heart and Diabetes Institute in Melbourne, said the overload hypothesis made sense on a number of levels because while maternal obesity might have a direct impact, it was probably a proxy for childhood obesity, as obese mothers tended to have obese children.

“It is certainly a good idea for the mother not to be overweight during pregnancy for other very well established reasons, but maintaining good health and a healthy weight of the young child is also likely to be beneficial,” he said.

“There is evidence that children developing type 1 diabetes have a higher BMI now than they did 20 years ago. And obesity will lead to a degree of insulin resistance,” Professor Shaw said.

The rate at which diabetes incidence was increasing in Australia was also 3% to 5% annually and was higher than for type 2 diabetes, he said.

A report released last week on the incidence of type 1 diabetes in Australia between 2000 and 2008 showed the incidence of of the disease had risen sharply between 2000 and 2004 but had plateaued since 2005.

According to the Australian Institute of Health and Welfare report Australia is among the top ten countries with the highest rates of type 1 diabetes in the world.

Arch Pediatr Adolesc Med 2010; 164:732-8.
Posted 9 August, 2010

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