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Prenatal and early childhood phthalate exposures and thyroid function among school-age children
Kyoung-Nam Kim1, Hwa Young Kim2, Youn-Hee Lim3
1Department of Preventive Medicine, Seoul National University College of Medicine, Seoul, Republic of Korea; Division of Public Health and Preventive Medicine, Seoul National University Hospital, Seoul, Republic of Korea.
Insights
Early life exposure to phthalates, chemicals found in plastics, may impact children's thyroid function. This study linked prenatal and childhood phthalate levels to changes in thyroid hormones in school-aged children.
Area of Science:
- Environmental Health
- Endocrinology
- Toxicology
Background:
- Limited research exists on the connection between prenatal and early childhood phthalate exposure and thyroid function in children.
- Phthalates are common endocrine-disrupting chemicals with potential health implications.
Purpose of the Study:
- To examine the association between phthalate exposure during early life (prenatal and childhood) and thyroid function in school-aged children.
- To utilize longitudinal data from a prospective cohort to understand these relationships over time.
Main Methods:
- Urinary phthalate metabolite levels were measured during pregnancy and at ages 2, 4, and 6 years.
- Thyroid function tests (TSH, T3, fT4) were conducted at age 6.
- Associations were analyzed using linear regression and Bayesian kernel machine regression (BKMR) models in 492 children.
Main Results:
- Higher prenatal mono-n-butyl phthalate (MnBP) and early childhood mono-(2-ethyl-5-oxohexyl) phthalate (MEOHP) exposures were linked to lower thyroid-stimulating hormone (TSH) levels.
- Certain phthalate metabolites at ages 2 and 6 years were associated with elevated triiodothyronine (T3) levels.
- Prenatal MnBP and early childhood MEHHP and MEOHP exposures were associated with lower free thyroxine (fT4) × TSH index.
Conclusions:
- Early life phthalate exposure appears to influence thyroid function in school-aged children.
- Findings suggest potential endocrine disruption effects of phthalates on the thyroid axis.
- Results should be interpreted with caution due to the use of single spot urine samples for exposure assessment.
Background:
Limited studies have investigated the association between prenatal and early childhood phthalate exposures and thyroid function among children.
Objectives:
To investigate the association between early life phthalate exposure and thyroid function among school-age children, considering both prenatal and early childhood exposures, using longitudinal data from an established prospective cohort.
Methods:
We measured urinary phthalate metabolite levels during pregnancy and at 2, 4, and 6 years of age and conducted thyroid function tests at 6 years of age. We assessed the associations between phthalate metabolite levels and thyroid function using linear regression and Bayesian kernel machine regression (BKMR) models (n = 492).
Results:
In linear regression models, a doubling of urinary mono-n-butyl phthalate (MnBP) levels, measured during pregnancy and at 4 years of age, was associated with lower thyroid-stimulating hormone (TSH) levels at 6 years of age (-5.0%, 95% confidence interval [CI]: -8.8%, -1.0% and -5.7%, 95% CI: -9.7%, -1.5%, respectively). A similar association was found between mono-(2-ethyl-5-oxohexyl) phthalate (MEOHP) levels at 4 years of age and TSH levels at 6 years of age (-5.5%, 95% CI: -9.7%, -1.1%). Urinary mono-(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP) (2.3%, 95% CI: 0.1%, 4.5%) and MEOHP levels at 2 years of age (2.2%, 95% CI: 0.1%, 4.4%) and mono-2-ethyl-5-carboxypentyl phthalate (1.4%, 95% CI: 0.1%, 2.7%) and mono-benzyl phthalate levels at 6 years of age (1.1%, 95% CI: 0.4%, 1.9%) were associated with higher triiodothyronine (T3) levels at 6 years of age. Urinary MnBP during pregnancy, MEHHP, MEOHP, and MnBP at 4 years of age were also associated with lower free thyroxine (fT4) × TSH. In BKMR models, urinary MnBP levels during pregnancy were associated with lower TSH levels and fT4 × TSH (both posterior inclusion probabilities: 0.99).
Conclusions:
Our findings suggest that early life phthalate exposure influences subsequent thyroid function. However, the results should be interpreted cautiously, because a single spot urine sample was used to quantify the phthalate exposures at each time point.
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