Blood leukocyte DNA methylation of circadian genes in relation to environmental phthalate exposure in Mexican adolescents.

BACKGROUND

Phthalates are endocrine-disrupting chemicals that have been linked to circadian disruption; however, associations between phthalate exposure and DNA methylation of circadian genes during adolescence remain poorly understood.

METHODS

We analyzed 488 adolescents (mean age = 15.4 years; 53.1% female) enrolled in the ELEMENT cohort. Urinary and blood samples were collected in 2015 to measure urinary phthalate metabolites and blood leukocyte DNA methylation (DNAm), respectively. Metabolites were grouped into summary phthalate mixtures, and DNAm was measured at 334 CpG sites across nine circadian genes using the Infinium MethylationEPIC BeadChip. Multivariable linear regression models were adjusted for urinary specific gravity, sociodemographic factors, and immune cell composition. Nominal associations were defined as p < 0.05 , and false discovery rate (FDR) correction was applied across CpG sites, with q < 0.10 considered statistically significant. Sex-stratified analyses were also performed.

RESULTS

In the overall sample, three associations met the FDR threshold. Higher urinary concentrations of Σ DEHP and Σ plastic phthalates were associated with lower DNAm at BMAL1 cg09404790 (q = 0.0419 and 0.0650, respectively), whereas higher Σ AA phthalate concentrations were associated with higher DNAm at BMAL1 cg14666553 (q = 0.0667). In sensitivity analyses, these associations remained directionally consistent and nominally significant after additional adjustment for dietary patterns and assessment time of day, but none retained FDR-adjusted significance. Among males, seven associations met the FDR threshold, including inverse associations of Σ AA and Σ DBP phthalates with DNAm at CRY1 cg06205108 and cg03853227 (q = 0.0058-0.0600) and additional associations involving BMAL1 (cg05239841; q = 0.0389) and CRY2 (cg26742859; q = 0.0650). Among females, one association met the FDR threshold, with higher Σ plastic concentrations associated with higher DNAm at a CRY1 locus (q = 0.0067).

CONCLUSIONS

Urinary phthalate mixture concentrations were associated with DNAm at selected circadian gene loci in this cross-sectional sample of Mexican adolescents. Differences in the number and pattern of associations across sex strata warrant further investigation in larger longitudinal studies with formal tests of interaction.