WEDNESDAY, Feb. 4 (HealthDay News) -- The melamine-tainted infant formula in China that sickened more than 50,000 kids last fall resulted in more than 10 percent of the youngest ones developing kidney problems, according to just-released Beijing research on the scandal.

About 20 percent of melamine-exposed infants in Taiwan and 10 percent of those who drank the formula in Beijing ended up getting kidney stones. And children born prematurely had an even greater risk, concluded the authors of a study released online Wednesday in the New England Journal of Medicine and scheduled to appear in the journal's March 12 print issue.

"We've had reports of roughly the number of children affected, but this is the first report that is more systematically looking at the ramifications of the exposure in kids," said Dr. Michael Somers, a pediatric nephrologist with Children's Hospital Boston and a spokesman for the American Society of Pediatric Nephrology. "This is from the hospital in Beijing, which is their equivalent of a big academic hospital with very good pediatric nephrology."

The children involved in the study all survived and are basically thriving after their encounter with melamine-contaminated formula, said Dr. Craig B. Langman, author of an accompanying editorial and a kidney diseases professor at the Feinberg School of Medicine at Northwestern University in Chicago.

Less is known about the children who fared poorly. And their future remains unclear, Langman said in his editorial.

Much more study needs to be done, he wrote, "before we know whether apparently thriving children have a major ongoing health risk from previous melamine exposure through their infant formula."

Melamine is an industrial chemical found in plastics and other products. It was added to infant formula and other foods in mainland China to boost the protein content and help the products pass muster on food-quality tests.

Since September, such melamine-contaminated baby formula sickened more than 54,000 children and is being blamed for at least four deaths in Asia.

The chemical has turned up in dairy products sold across Asia and, to a lesser extent, in Europe and in the United States.