Inverse associations of bisphenol A and phthalate metabolites with serum bilirubin levels in Korean population

Bisphenol A (BPA) and phthalates are endocrine disruptors that can induce oxidative stress. Serum bilirubin has antioxidant properties and may serve as a biomarker of oxidative stress. The objective of this study was to explore the relationship of BPA and phthalates with serum bilirubin levels in a Korean population. Urinary concentrations of BPA and six phthalate [mono-n-butyl phthalate (MnBP), mono-iso-butyl phthalate (MiBP), mono-(2-ethyl-5-oxohexyl) phthalate (MEOHP), mono-(2-ethyl-5- hydroxyhexyl) phthalate (MEHHP), mono-(2-ethyl-5-carboxypentyl) phthalate (MECPP), and mono-benzyl phthalate (MBzP)] were measured in 709 participants. Serum concentrations of BPA and three phthalate metabolites [MnBP, MiBP, and mono-(2-ethylhexyl) phthalate (MEHP)] were measured in 752 participants. After excluding missing variables, associations between above chemicals and serum bilirubin levels were analyzed using multivariate linear regression with age, sex, BMI, GGT, GOT, GPT, and alcohol intake adjustment. Participants were further stratified by sex. Among the urinary chemicals, BPA and four phthalate metabolites (MnBP, MEOHP, MEHHP and MECPP) were inversely associated with serum bilirubin levels (BPA: beta = - 0.071, P < 0.0001; MnBP: beta = - 0.055, P = 0.025; MEOHP: beta = - 0.101, P < 0.0001; MEHHP: beta = - 0.106, P < 0.0001; MECPP: beta = - 0.052, P = 0.003). In a case of serum chemicals, only MiBP showed significantly positive association (beta = 0.036, P = 0.016). After stratification by sex, the associations of urinary BPA remained both in male and female, of which urinary phthalates disappeared in female. The association of serum MiBP was disappeared after stratification. Urinary BPA and phthalate metabolites were inversely associated with serum bilirubin levels, whereas serum MiBP showed positive association with bilirubin. These results could provide clues for understanding the mechanisms of endocrine disruptor from oxidative stress to excretion from our body.