Figure. Consumption of hot noodle soup in melamine (MEL) or ceramic (CER) bowls and excretion of urinary melamine among 12 study subjects. A, Mean (SE) temporal change of urinary melamine levels in the MEL and CER groups. N indicates the number of urine specimens collected in that particular 2-hour interval after consuming hot noodle soup. B, Mean (SE) total melamine excretion in urine 12 hours after consumption by treatment sequence (group A: treatment MEL then CER; group B: treatment CER then MEL). C, Mean (SE) cumulative urinary melamine excretion for 2-hour intervals in the MEL or CER groups.
Wu C-F, Hsieh T-J, Chen B-H, Liu C-C, Wu M-T. A crossover study of noodle soup consumption in melamine bowls and total melamine excretion in urine.. JAMA Intern Med.. Published online January 21, 2013. doi:10.1001/jamainternmed.2013.1569
eFigure 1. The temporal change of urinary melamine levels among the 16 healthy subjects after consuming a hot noodle soup in one melamine bowl
eFigure 2. Pictures of melamine and ceramics bowls
eFigure 3. Amount of melamine excretion in urine before noodle consumption by treatment sequence
Wu C, Hsieh T, Chen B, Liu C, Wu M. A Crossover Study of Noodle Soup Consumption in Melamine Bowls and Total Melamine Excretion in Urine. JAMA Intern Med. 2013;173(4):317-319. doi:10.1001/jamainternmed.2013.1569
Author Affiliations: Colleges of Health Sciences (Drs C.-F. Wu and M.-T. Wu) and Medicine (Drs Hsieh, Chen, and Liu), Kaohsiung Medical University, Kaohsiung, Taiwan; and Department of Family Medicine, Kaohsiung Medical University Hospital, and Center of Environmental and Occupational Medicine, Kaohsiung Municipal Hsiao-Kang Hospital, Kaohsiung (Dr M.-T. Wu).
Melamine exposure remains common even after the 2008 melamine-tainted baby formula incident, which resulted in 6 deaths and approximately 50 000 hospitalizations.1 A continuous low-dose melamine exposure has been linked to urolithiasis in both children and adults.2,3 Another source of melamine exposure is melamine tableware.4 In a pilot study, we asked 16 healthy volunteers (age range, 20-27 years) to consume 500 mL of hot noodle soup (initial temperature, 90°C) served in melamine bowls in the morning of October 2011. We collected from each participant 1 spot urine sample immediately before and at 2-hour intervals for 12 hours after consuming the noodle soup. This experiment simulated the natural situation; thus, not all participants provided urine samples at every 2-hour interval. However, all urine samples from all participants were collected after consumption for 12 hours. Postconsumption mean urinary melamine concentrations, corrected for urinary creatinine, initially increased sharply, peaked at 4 to 6 hours, and then declined sharply for 2 hours and then less steeply for the remainder of the monitoring period (eFigure 1). We therefore investigated if consumption of hot noodle soup served in melamine bowls would increase total urinary melamine excretion.
In a randomized 2 × 2 crossover study in December 6, 2011, we asked 1 group (3 men and 3 women [group A]) to fast for 8 hours before consuming 500 mL of hot noodle soup (initial temperature, 90°C) served in a melamine bowl as a 30-minute breakfast. The study design was the same as the aforementioned pilot study. We collected spot urine sample before and at 2-hour intervals for 12 hours after consumption. Another group (3 men and 3 women [group B]), following the same procedures, consumed the same soup from ceramic bowls (eFigure 2), in which melamine levels were nondetectable.4 All subjects were different from those of the pilot study and were advised not to use any melamine tableware 3 days before the experiment. Soft drinks were not restricted. After a 3-week washout period, the assigned treatments were reversed (December 27, 2011). This study had institutional review board approval, and each participant provided written informed consent.
Urinary melamine levels were measured by triple-quadrupole liquid chromatography tandem mass spectrometry. The method of detection limit (MDL) was 0.8 ng/mL (parts per billion) in urine, with any measurement below the MDL treated as 0.4 ng/mL.3 Total melamine excretion was calculated as melamine concentration of 1-spot urine sample × the amount of that spot urine and the amounts of all the urine samples collected for 12 hours after the participant consumed hot noodle soup were summed. A Wilcoxon signed rank test was used to examine the absolute differences of total melamine excretion between the 2 groups, whereas a Wilcoxon rank sum test was used to compare the differences of total melamine excretion in the 2 melamine or ceramic groups. P values were 2-sided, with a significance level of .05.
Twelve healthy people (6 men and 6 women; age range, 20-27 years) participated. All urine samples from all participants were collected after consumption for 12 hours in both groups. Temporal change in mean urinary melamine concentration corrected for urinary creatinine was similar to the previous pilot study (Figure, A; eFigure 1). The mean (range) and total number of postconsumption spot-urine specimens collected from melamine bowl users were 4.3 (1-13) and 52, respectively; all melamine concentrations were detectable. In contrast, the mean (range) and total number of postconsumption spot-urine specimens collected from ceramic bowl users were 4.3 (2-7) and 51, respectively, but melamine concentrations in 17 urine samples (33%) were below the MDL. Total melamine excretion (mean [SE]) in urine for 12 hours was 8.35 (1.91) μg and 1.31 (0.44) μg in melamine bowls and ceramic bowls, respectively (Figure, B). The difference was statistically significant (7.04 [1.62] μg; P < .001). In contrast, there was no significant difference in the 2 melamine groups (P = .78), although a significant difference was noted in the 2 ceramic groups (P = .02) (Figure, B). The significance was probably due to the high melamine excretion (carryover effect) in the urine samples prior to consumption in the 2 ceramic groups (eFigure 3). The estimated half-life of urinary melamine elimination was approximately 6 hours (Figure, C).
Melamine tableware may release large amounts of melamine when used to serve high-temperature foods. The brand of melamine bowls used in this study was chosen from the 5 brands we tested previously.4 The amount of melamine released into food and beverages from melamine tableware varies by brand, so the results of this study of 1 brand may not be generalized to other brands. The use of nonbreakable melamine tableware is common in our daily life. Although the clinical significance of what levels of urinary melamine concentration has not yet been established, the consequences of long-term melamine exposure still should be of concern.5
Correspondence: Dr M.-T. Wu, College of Health Sciences, Department of Family Medicine, Kaohsiung Medical University Hospital, Chih-Shih Building, No. 100 Shih-Chuan First Rd, Room 917, Kaohsiung 807, Taiwan (firstname.lastname@example.org).
Published Online: January 21, 2013. doi:10.1001/jamainternmed.2013.1569
Author Contributions: Dr M.-T. Wu had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. Study concept and design: C.-F. Wu, Hsieh, Liu, and M.-T. Wu. Acquisition of data: Chen, Liu, and M.-T. Wu. Analysis and interpretation of data: C.-F. Wu, Liu, and M.-T. Wu. Drafting of the manuscript: C.-F. Wu and M.-T. Wu. Critical revision of the manuscript for important intellectual content: Hsieh, Chen, Liu, and M.-T. Wu. Statistical analysis: C.-F. Wu and M.-T. Wu. Obtained funding: Chen and M.-T. Wu. Administrative, technical, and material support: Hsieh, Chen, Liu, and M.-T. Wu. Study supervision: M.-T. Wu.
Conflict of Interest Disclosures: None reported.
Funding/Support: This study was supported by the Taiwan National Health Research Institutes (NHRI-EX98-9708PI), the National Science Council (NSC100-2314-B-037-027), and Kaohsiung Medical University Hospital (KMUH98-8R05 and KMUH100-9R54).
Role of the Sponsors: The Taiwan National Health Research Institutes and the National Science Council were involved in supporting the design and conduct of the study; and the Kaohsiung Medical University Hospital assisted with the collection, management, analysis, and interpretation of the data as well as the preparation, review, and approval of the manuscript.
Additional Contributions: Chao-Yi Chien, MS, and Meng-Tian Tsai, MS, assisted with laboratory analyses, and James Steed, BS, assisted in editing the manuscript.