Age-Specific Association Between Urinary Phthalate Metabolites and Diabetes Mellitus: Findings from the Korean National Environmental Health Survey Cycle 4 (2018–2020)

Background/Objectives: Phthalates are encountered in everyday consumer and indoor environments, and their metabolites are commonly detected in urine. Although phthalate exposure has been linked to diabetes mellitus (DM), associations may vary by life stage. Therefore, we evaluated age-specific association between urinary phthalate metabolites and DM using nationally representative Korean data. Methods: We conducted a cross-sectional analysis of the Korean National Environmental Health Survey Cycle 4 (2018–2020). Adults aged ≥19 years with complete data were included. Eight urinary metabolites were evaluated. Metabolites were log-transformed, and those showing interaction were analyzed by tertiles. Complex survey-weighted logistic regression estimated odds ratios (95% confidence intervals) for DM, adjusting for demographic, socioeconomic, and health behavior factors. Analyses were stratified by age group. Results: Geometric mean (GM) concentrations among participants with DM varied significantly by age groups for several metabolites. Interaction analyses identified statistically significant effects for selected phthalate metabolites, including MnBP, MCPP, and MEP. In the age-stratified adjusted models, MnBP and MCPP were more strongly associated with DM in young adults, whereas the pattern for MEP appeared more evident in older adults, suggesting potential life-course differences in metabolic vulnerability. Conclusions: Associations between urinary phthalate metabolites and DM vary substantially by age, indicating life-course differences in exposure pathways and metabolic vulnerability. Age-specific prevention and surveillance strategies may improve environmental health interventions for DM.