Melamine-tainted infant formula linked to kidney stones

Last September, Chinese officials acknowledged that months-long illegal use of a fraudulent protein substitute — melamine — had poisoned powdered infant formula that was sold throughout the country. Some 300,000 children are believed to have consumed the tainted product, in some cases for more than a year. Overall, an estimated 1,200 infants and toddlers were sickened. Six died. Today, a Chinese study and two related research letters — all released early by the New England Journal of Medicine — tie infant exposure to melamine with a greatly elevated risk of kidney stones.

An epidemic of kidney stones had been reported previously among these children. Until now, however, the risk of stone formation had not been quantified — nor linked, especially, to consumption of the most-heavily tainted infant formula.

The primary study that was just released involved an examination of nearly 600 children in Beijing. It turned up none of the conventional urinary chemicals that mark stone formation. Sand-size calcifications were only identified in the children through the use of ultrasound. This suggests, the authors say, melamine may trigger the formulation of atypical stones — ones having an unusual chemical recipe.

An accompanying letter by researchers in Taiwan who had screened more than 1,100 children last fall also found that development of kidney stones was “significantly more frequent in the high-exposure group” — children drinking infant formula with the highest concentrations of melamine. However, in this survey, the ostensibly high-exposure group consisted of youngsters drinking formula tainted with anything over 2.5 ppb melamine. In the Beijing population, highly tainted formulas had more than 500 ppb melamine, and even the moderate exposure group was 1 to 500 ppb.

Hong Kong-based researchers performed ultrasound tests looking for evidence of kidney stones in an even larger group of asymptomatic children  — 2,140 — and over a broader age range: to age 12. They confirmed the presence of a stone in only one child (age not given), and noted signs of possible stone formation in six additional kids (again, age not given). This group extended its survey to older children since reports emerged of melamine contamination in some milk products. No putative melamine-exposure estimates were reported for any of the children.

“It is remarkable that all three reports describe the absence of conventional symptoms and signs related to [kidney stones],” notes Craig B. Langman of the Northwestern University School of Medicine in an accompanying editorial.

Indeed, authors of the Beijing study observe: “These findings contrast with the present guidelines posted on the Web site of the Ministry of Health of China (, which suggest that symptoms are useful in diagnosing the presence of stones. Our results indicate that screening for urinary stones should be based on the history of exposure to melamine rather on the symptomatology.”

Taken together, the three new reports suggest stone formation rates were generally low, since the majority of youngsters who had consumed even the most tainted formulas failed to develop them. That said, in Beijing-area children exposed to the most contaminated milk, stone formation was roughly seven times higher than in the local children who had been drinking melamine-free infant formula. What’s more, in this Beijing study, infants who had been born prematurely were 4.5 times more likely to develop stones than were babies who had been born full-term.

China, though slow to act in acknowledging the melamine crisis, ultimately responded with stern punishments. According to a New York Times report, on January 22 two people linked to the poisoning incident were sentenced to death. Three more received a life sentence in prison, another received a suspended death sentence, and 15 people ended up with sentences of between 2 and 15 years in jail.

Janet Raloff is the Editor, Digital of Science News Explores, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer, specializing in toxicology. To her never-ending surprise, her daughter became a toxicologist.

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