New York (Reuters Health)-A study on the risk of kidney disease in Chinese children exposed to melamine-contaminated milk was published in the New England Journal of Medicine. Studies have shown that exposure to melamine-contaminated formula milk can increase the risk of urinary tract stones by up to seven times, but these stones usually do not produce any symptoms or laboratory abnormalities, and their clinical relevance is unclear.
Melamine is a colorless crystalline organic compound rich in nitrogen. It is widely used in the manufacture of materials such as plastics, adhesives, countertops and tableware.
In China where pollution occurs, people add water to raw milk to increase its volume. Due to this dilution, the protein concentration of milk is lower.
Companies that use milk for further production (such as infant formula) often check protein levels through tests that measure nitrogen content. The addition of melamine increases the nitrogen content of milk, so its protein content seems to be higher than the actual content.
The addition of melamine to food has not been approved by the FAO/WHO Codex Alimentarius Commission (Food Standards Committee) or any national authority.
Although there are no direct human studies on the effects of melamine, data from animal studies indicate that melamine can cause bladder stones.
When combined with cyanuric acid that may also be present in melamine powder, melamine can form crystals, which can cause kidney stones. These small crystals can also block the tubules in the kidneys, which may prevent the production of urine, leading to kidney failure, and in some cases even death.
Melamine has also been shown to have carcinogenic effects on animals in some cases, but there is not enough data to judge the risk of carcinogenesis to humans.
Last year, the incidence of urolithiasis (stone formation in the kidneys, bladder and urinary tract) among young children in China rose sharply. The government announced in September that the outbreak was most likely caused by melamine contamination in formula milk.
In their study, Dr. Jie Ding of Peking University First Hospital and his colleagues described an investigation that ultimately linked melamine exposure to urolithiasis in young children. The study involved a parental survey of 589 children 36 months or younger who were being screened for melamine exposure and symptoms of urinary calculi. Standard urinary function tests and ultrasound examinations were also performed.
A total of 421 children consumed formula milk contaminated with melamine. Fifty children were diagnosed with stones, of which 8 had not been exposed to melamine, 112 had suspected stones, and 427 had no stones.
Blood cells and white blood cells were found in the urine of 5.9% and 2.9% of children with stones, respectively, which is equivalent to the proportion of children without stones.
In addition, blood creatinine, urea nitrogen, and alanine aminotransferase levels are usually normal in patients with stones. Only 4 of 41 stone patients had urine markers that suggested glomerular dysfunction.
Children exposed to formula with high melamine content (>500 ppm) are 7.0 times more likely to develop urinary stones than children with formula not contaminated with melamine. Premature babies are 4.5 times more likely to have stones than full-term babies.
In a related letter, a team from the Chinese University of Hong Kong reported that only one of the 2,140 children who underwent ultrasound examinations between September 28 and October 17, 2008 was found to have urolithiasis. They added that some children have also found other abnormalities, but their clinical significance (if any) is unclear.
According to a related editorial, the American Academy of Pediatric Nephrology recommends conservative treatment for asymptomatic infants, "because it is speculated that melamine-induced stones seem to be easily excreted after rehydration", and due to the lack of long-term follow-up data.
Dr. Craig B. Langman, an editorial author at Northwestern University in Chicago, commented that ultrasound testing of all potentially exposed Chinese children currently living in the United States is unlikely to be cost-effective.
Source: New England Journal of Medicine, first online on February 4, 2009.
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