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(adjusted R2=0.096)Betaa−0.06 0.10 0.06 −0.05 0.14 0.20 0.02 −0.07 0.04 0.07 (adjusted R2=0.137)Betaa−0.14 0.06 0.07 −0.14 0.18 0.19 0.09 0.02 0.04 0.01 256have shown an inverse association between cobalt and obesity/overweight rates, regardless of age, gender, and type of the biological samples. Among them, five studies assessed only children10-14), one study had no age limitation15), and two studies assessed adults16, 17). Consistent with the present study, Padilla (2010)15), Shao (2017)11), and Vrijheid (2020)14) reported an inverse association between UCo levels and child-hood BMI and weight. Błażewicz (2013)10) showed lower plasma and blood cobalt concentrations in children with obesity than in those without obesity; Figure 2　Pearson correlation coefficients between urinary cobalt concentration (UCo) and BMI in 860 boys and 682 girlsTable 3　 Relationships of log UCo and other variables to BMI: Multiple linear regression analysis Log UCoAge (months)Birthweight (g)Average sleep duration (hours)Father’s BMIMother’s BMIParental smoking (Yes=1, No=0)Father’s education (years)Mother’s education (years)Annual household incomea Standardized partial regression coefficientby the forced-entry methodBoysp-value<0.0010.075 0.033 <0.001<0.001<0.0010.013 0.685 0.291 0.784 however, the study failed to demonstrate the same results for UCo. Similarly, Vigeh (2017) and Skalnaya (2018) reported higher levels of hair cobalt in chil-dren and adults with low body weight than in those with normal weight13, 17). In adult women and chil-dren, an inverse correlation has been reported between cobalt levels in the toenail16) and serum12), respectively, and BMI. In addition, experimental studies (mice and rats) have shown that blood/urine/serum cobalt produce the same effects on animal weight/BMI18, 38). Thus, the findings of the current study and previous epidemiological/exper-Girlsp-value0.106 0.011 0.140 0.185 <0.001<0.0010.586 0.094 0.350 0.122