Abstract
Phthalates are pervasive endocrine-disrupting chemicals frequently introduced into the human body via contaminated food and food-contact packaging. During pregnancy, adequate maternal thyroid hormone concentrations are vital for fetal somatic and neurodevelopment; however, dietary exposure to phthalates may impair thyroid homeostasis. This cross-sectional study evaluated dietary sources of phthalate exposure and quantified their associations with serum thyroid hormone levels among 348 pregnant women (gestational weeks 12–18) recruited from an urban Canadian cohort in the Greater Montreal Area. Dietary intake was assessed using a validated semi-quantitative food frequency questionnaire tailored to packaged and ultra-processed food consumption. Urinary concentrations of eleven phthalate metabolites were determined using liquid chromatography-tandem mass spectrometry (LC-MS/MS), and serum thyroid-stimulating hormone (TSH), free thyroxine (FT4), and free triiodothyronine (FT3) were measured via automated immunoassay. Frequent consumption of ultra-processed meats, high-fat dairy, and packaged fast foods was significantly associated with elevated urinary concentrations of di(2-ethylhexyl) phthalate (DEHP) and diisononyl phthalate (DiNP) metabolites (p < 0.01). In multivariable linear regression models adjusted for maternal age, gestational age, body mass index, urinary creatinine, and dietary iodine intake, each interquartile range increase in molar sum of DEHP metabolites was associated with a 4.12% decrease in serum FT4 (95% CI: −6.84%, −1.32%) and a 7.35% increase in serum TSH (95% CI: 1.88%, 13.10%). These findings highlight diet as a major modifiable vector of phthalate exposure in pregnant Canadian women and demonstrate an inverse association with circulating thyroid hormone levels, emphasizing the need for targeted nutritional guidance and updated food packaging regulations.
