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Type 1 diabetes hits children and babies more in wealthy New Zealand suburbs than in poor ones, a study has revealed.
It is the first research of its type on the rapidly escalating auto-immune disease in New Zealand, confirming studies overseas on its social and economic distribution in western nations.
The study, presented to a diabetes conference in Wellington yesterday, is based on 25 years of registrations at Christchurch Hospital of newly diagnosed Canterbury children aged up to 14.
It shows a 25 per cent drop in incidence between the wealthiest and poorest areas.
"There are all sorts of factors that might explain this," said hospital scientist Dr Jinny Willis, who conducted the study with colleagues from Otago and Canterbury Universities.
The Canterbury type 1 diabetes register also shows that the region is experiencing annual increases of 5 per cent, two-thirds higher than the western country average of 3 per cent. About 15,000 people in New Zealand have type 1 diabetes.
Dr Willis said the hygiene hypothesis was widely accepted in medical and scientific circles as a likely explanation for the rapid increases in the incidence of type 1 diabetes.
This theory is also used to try to explain high rates of asthma in western countries.
It holds that because infections are now relatively well controlled in the west, compared with a century or more ago, the immune system in some people starts attacking some part of the body, in the case of type 1 diabetes the pancreatic cells which produce insulin.
Dr Willis said that, based on the hypothesis, the higher incidence in more-affluent areas might be because of differences in factors like family size or patterns of child-care use - things that exposed a child more, or less, to other people and their infections.
Vitamin D deficiency was considered a possible factor in developing type 1 diabetes and plans were being developed overseas for a large, powerful study, including New Zealand, to test this idea, Dr Willis said.
