Scientists from Peking University in Beijing reached their conclusion after examining ultrasound images of almost 8,000 children under the age of three living near the rural headquarters of Sanlu Group, the company at the centre of the 2008 scandal.
An estimated 300,000 children were sickened and six died as a result of consuming dairy products laced with melamine. The industrial chemical was added to thousands of tonnes of watered-down milk to fool inspectors testing for protein content and increase profits in one of the most high-profile contamination issues in recent years.
The research, by Jian-meng Liu et al, appears in the Canadian Medical Association Journal. It raises the possibility that 36,000 children could have suffered “renal abnormalities” for up to six month after drinking contaminated milk.
The paper, entitled Urinary tract abnormalities in Chinese rural children who consumed melamine-contaminated dairy products: a population-based screening and follow-up study, said that the long-term effects remain unknown and called for more research into the matter.
"The potential for long-term complications after exposure to melamine remains a serious concern," said the study. "Our results suggest a need for further follow-up of affected children to evaluate the possible long-term impact on health, including renal function."
After carrying out ultrasound screenings of 7,933 children, the researchers found 48 were suffering from kidney stones or swollen kidneys. The researchers monitored most of these children at intervals of one, three and six months and found that "renal abnormalities" remained in 12 percent of the children.
The scientists said the results may have implications for the broader population of children who had exposure to melamine.
"Among the 300,000 affected children, although they don't have symptoms, maybe 12 percent will have abnormal ultrasound images after six months," said researcher Dr Liu Jianmeng.
One of the major strengths of the study is that it focused on the main distribution areas of Sanlu products, whose population probably had the highest exposure to melamine in the world, said the researchers.
“Therefore, the estimated prevalence of renal damage in our study represents the risk of renal damage in a population after heavy exposure to melamine”, they added.
However, Liu said, that some limitations in the study - such as not all children in the area were screened - could have led to a slight overestimation on the prevalence of such abnormalities.
Dr Peter Ben Embarek, a World Health Organization food safety expert based in Beijing, told the Associated Press: "There is a need for these types of follow-up studies to better understand what the long-term effect is of high exposure to melamine."
Chinese authorities recently launched another food safety crackdown after contaminated milk products confiscated during the scandal began to resurface. Last week, the Government said all such product had now been destroyed.
Source: Canadian Medical Association Journal. Urinary tract abnormalities in Chinese rural children who consumed melamine-contaminated dairy products: a population-based screening and follow-up study. Authors: Jian-meng Liu, Aiguo Ren, Lei Yang, Jinji Gao, Lijun Pei, Rongwei Ye, Quangang Qu , Xiaoying Zheng