Children who get obesity-related diabetes face a much higher risk of kidney failure and death by middle age than people who develop diabetes as adults, a study suggests.

The study offers some of the first strong evidence of the consequences of the nation's growing epidemic of type 2 diabetes in children, said Dr. William Knowler, a co-author and researcher with the National Institute of Diabetes and Digestive and Kidney Diseases.

The research also lends support to warnings that diabetes and other obesity-related ills are on the verge of shortening average life span in the United States.

The study involved Pima Indians in Arizona, who have disproportionately high rates of diabetes and obesity. They may be "the tip of the iceberg, letting us know what's in the future for the rest of America if we don't do something about the childhood obesity epidemic," said Dr. David Ludwig, director of Children's Hospital Boston's obesity program. He was not involved in the research.

The study appears in Wednesday's Journal of the American Medical Association.

It involved a group of Indians whom National Institutes of Health researchers have been tracking since 1965. Of the 1,865 participants with Type 2 diabetes, 96 developed it in childhood. The average age of youth-onset diabetes was about 17 years, although the disease was diagnosed in children as young as 3 1/2.

During at least 15 years of follow-up, 15, or 16 percent, of those with childhood-onset type 2 diabetes developed end-stage kidney failure or died from diabetic kidney disease by age 55. That compared with 133, or 8 percent, of those who developed diabetes after age 20.

The researchers calculated that the incidence of end-stage kidney failure and death by age 55 was nearly five times higher in people who developed type 2 diabetes before age 20 than in those who developed diabetes in adulthood.

Most of the 20 million Americans with diabetes are adults with type 2. While a generation ago, type 2 diabetes was almost unheard of in children, the incidence has increased substantially in the past decade, largely because of obesity and lack of exercise.

Diabetes impairs the body's ability to regulate blood sugar levels. That can lead to damage to the kidneys and blood vessels throughout the body.

When type 2 diabetes develops earlier in life, it has many more years to cause damage and can lead to premature complications and death, the researchers said.

The American Diabetes' Association's Dr. Larry Deeb said that may not be the only explanation. During adolescence, kidneys are still maturing and may be particularly vulnerable to diabetes' effects, said Deeb, a pediatrics professor at the University of Florida.

While Pima Indians are among ethnic groups believed to have a genetic predisposition toward diabetes and obesity, the researchers said the results probably apply to others as well.

And even in people with a genetic predisposition, weight control and physical activity can help delay the onset of type 2 diabetes.

A recent study by pharmacy benefits manager Express Scripts Inc. found that prescriptions for type 2 diabetes drugs doubled among U.S. children ages 5 to 19 from 2002 to 2005.