(Adds dropped word 'five' in lead)
Feb 4 (Reuters) - The number of cases of insulin-requiring type 1 diabetes rose sharply in children under the age of five in Philadelphia over a two decade span, paralleling increases seen across the United States and in Europe, according to a U.S. study.
Researchers whose work appeared in the journal Diabetes Care found that the number of children under five diagnosed with type 1 diabetes increased 70 percent in 2005 from 1985, when a registry of such patients was begun.
The number of diagnosed cases among all children up to age 14 rose by 29 percent.
"Why are we seeing this large increase in type 1 diabetes in very young children? Unfortunately, the answer is we don't know," said lead author Terri Lipman, a professor at the University of Pennsylvania School of Nursing.
Of the two most common forms of diabetes, type 2 typically affects adults who can still produce insulin, but whose bodies cannot use the hormone to regulate blood sugar. Type 1, previously known as juvenile diabetes, typically strikes children whose immune systems have killed off insulin-producing cells in the pancreas. The disease is usually fatal if left untreated.
In 1985, according to a registry of Philadelphia children diagnosed with type 1 diabetes, 13.4 out of every 100,000 children in Philadelphia was newly diagnosed with the disease. In 2004, the rate was 17.2 cases per 100,000.
Type 1 diabetics must take insulin, but many type 2 diabetics can control the disease with medications, diet and exercise.
Type 1 diabetes tends to start in adolescence, but experts said parents need to be aware that toddlers and preschoolers are also susceptible, given the rising number of cases in very small children.
Children from Chicago to Colorado to Finland have similarly increased rates of type 1 diabetes, though the cause eludes researchers.
"This young group is a mystery," said Carol Levy, a type 1 diabetes specialist at Mount Sinai Hospital in New York who was not involved in the study.
"Make sure your child has a healthy lifestyle and maintains normal body weight, whether that's a guarantee we're going to reduce risk, we don't know at this point.
Several theories vie to explain the recent rise in diabetes among youth, including vitamin D deficiencies, lack of breastfeeding and over-hygienic environments that might cause the immune system to backfire.
"The data is controversial, so that's why I'm certainly very reluctant to propose a theory when nothing has been proven," Lipman told Reuters Health.
It is important to be aware of the symptoms of diabetes, which can include extreme thirst, bed wetting or accidents in toilet-trained children or excessively wet diapers in babies, said Lori Laffel, of the Joslin Diabetes Center in Boston.
By the time the disease is diagnosed, many infants and toddlers are very sick and the degree of illness tends to be more severe the younger the patient, experts noted.
"The young child isn't able to talk about symptoms," Laffel said. "A young child may be in diapers, you may not notice because diapers are often wet." SOURCE: http://bit.ly/YGkBuW (Reporting from New York by Trevor Stokes at Reuters Health; editing by Elaine Lies)