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Mariko HIRAIWA-HASEGAWA6), Kiyoto KASAI5, 7)Syudo YAMASAKI4), Shuntaro ANDO4, 5), Atsushi NISHIDA4), 2)Department of Forensic Science, Juntendo University, Faculty of Medicine, Tokyo, Japan3)Department of Epidemiology and Environmental Health, International University of Health and 1)Department of Epidemiology and Environmental Health, Juntendo University, Faculty of Medicine, Tokyo, Japan4)Department of Psychiatry and Behavioral Science, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan6)Department of Evolutionary Studies of Biosystems, School of Advanced Sciences, The Graduate University for Advanced Studies (SOKENDAI), Kanagawa, Japan5)Department of Neuropsychiatry, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan7)International Research Center for Neurointelligence (WPI-IRCN), The University of Tokyo, Tokyo, JapanJumpei TETSUKA1), Takehisa MATSUKAWA1, 2), Kazuhito YOKOYAMA1, 3), Cobalt and Childhood Body Mass IndexCorresponding author: Kazuhito YokoyamaDepartment of Epidemiology and Environmental Health, Juntendo University, Faculty of Medicine2-1-1 Hongo, Bunkyo-Ku, Tokyo, JapanTEL: +81-3-5802-1047　FAX: +81-3-3812-1026　E-mail: kyokoya@juntendo.ac.jp〔Received　Nov. 17, 2021〕〔Accepted　Feb. 2, 2022〕J-STAGE Advance published date: Jun. 20, 2022Copyright © 2022 The Juntendo Medical Society. This is an open access article distributed under the terms of Creative Commons Attribution License (CC BY), which permits unrestricted use, distribution, and reproduction in any medium, provided the original source is properly credited. doi: 10.14789/jmj.JMJ21-0043-OAObjectives: There are many reports on the effects of trace elements on human anthropometric characteristics. Among these elements, cobalt has consistently shown an inverse relationship with obesity risk. In the present study, we aimed to investigate the relationship between urinary levels of trace elements, focusing on cobalt, and childhood obesity, as indicated by the body mass index (BMI) in early adolescents, focusing on the participants’ gender.Design: A cross-sectional study was conducted in the Tokyo Teen Cohort study. Based on urinary samples, we obtained the anthropometric characteristics (weight and height) and potential covariates associated with childhood BMI for 1542 children (mean age=12 years; 860 boys and 682 girls).Methods: Concentrations of urinary cobalt and 17 other trace elements were measured using inductively coupled plasma-mass spectrometry or inductively coupled plasma-atomic emission spectrometry.Results: Pearson’s correlation coefficient revealed an inverse relationship between the log of cobalt concentrations in the urine and the BMI for the boys (r=−0.125, p<0.001) and girls (r=−0.082, p=0.033). Multivariate analysis, adjusted for various covariates, reconfirmed the correlation between urine cobalt and the childhood BMI, only in the boys (beta=−0.14, p<0.001).Conclusions: Among the 18 elements measured in the children’s urine, cobalt may exhibit sufficient potency to decrease the risk of childhood obesity, particularly in boys. Future studies are required to clearly determine the magnitude of the effect and the underlying mechanism(s).Key words: cobalt, trace elements, gender, childhood obesity, body mass indexJuntendo Medical Journal2022. 68(3), 251-260Original ArticlesEffects of Trace Elements on Anthropometric Characteristics of Children: IntroductionOver the past three decades, the frequency of childhood obesity has been increasing, leading to a Welfare Graduate School of Public Health, Tokyo, Japanworrisome epidemic worldwide1). Currently, it is estimated that more than 38 million children under the age of 5 years and 340 million children/adoles-cents aged 5-19 years are overweight or obese2). 251