Type 1 diabetes to double in European kids under 5

* Cases rising fastest in youngest children

* Study suggests environmental factors playing a role

By Julie Steenhuysen

CHICAGO, May 27 (Reuters) - The number of European children under 5 with type 1 diabetes could double by 2020, an alarming trend that suggests environmental factors may be playing a role, researchers said on Wednesday.

They said cases of type 1, or juvenile, diabetes in older children will rise significantly as well, and the findings likely apply to children in other regions.

They do not know what could be causing the increase.

"By 2020, the predicted number of new cases is 24,400, but this change is not shared evenly between the age groups, with incidence of type 1 diabetes in the youngest age group expected to double in both sexes," Dr. Chris Patterson of Queen's University in Belfast, Gyula Soltesz of Pecs University in Hungary and colleagues wrote in the Lancet medical journal.

Type 1 diabetes represents about 10 percent of the 180 million cases of diabetes globally. It occurs when the immune system goes haywire and starts destroying insulin-producing cells in the pancreas needed to control blood sugar.

These patients typically need daily insulin therapy to control their diabetes, which is a different disease from the far more common type 2 diabetes.