CHICAGO, April 14 (Reuters) - People with type 1 diabetes who got stem cell transplants were able to go as long as four years without needing insulin treatments, U.S. researchers said on Tuesday.

They said the process, which involves injecting people with stem cells made from their bone marrow cells, appears to have a lasting effect.

The study involved patients with Type 1 diabetes, formerly called juvenile diabetes, which occurs when the immune system goes haywire and starts attacking itself, destroying insulin-producing cells in the pancreas needed to control blood sugar.

These patients typically need daily insulin therapy to control their diabetes.

Dr. Richard Burt of Northwestern University's Feinberg School of Medicine in Chicago and colleagues first reported on the short-term success of the procedure, known as autologous non-myeloablative hematopoietic stem-cell transplantation, in 2007 but have since looked at how long it persisted.

Writing in this week's Journal of the American Medical Association they said 20 of 23 patients "became insulin free -- 12 continuously and eight transiently -- for periods as long as four years." The transient group of eight had to restart insulin at reduced levels.

The patients ranged in age from 13 to 31.

To find out if the change was lasting the research team said they measured levels of C-peptides, which show how well the body is producing insulin. They found those levels increased "up to 24 months after transplantation and were maintained until at least 36 months," their report said.

Even in the group which had to restart insulin there was still a significant increase in C-peptide levels that lasted at least two years, the researchers said.

They said the procedure was able to induce "prolonged and significant increases of C-peptide levels" in the small group of patients who were taking little or no insulin.

"At the present time (it) remains the only treatment capable of reversing type 1 diabetes mellitus in humans," the team wrote.

"Randomized controlled trials and further biological studies are necessary to confirm the role of this treatment in changing the natural history of (the disease)," they added.

(Editing by Julie Steenhuysen and Alan Elsner)