Table 4.
Effects of ethylparaben and methylparaben on thyroid function.
| Model | Exposure/Dose/Analyses | Main Results | References |
|---|---|---|---|
| Human | Urine samples were collected from patients at Wuhan Central Hospital who had thyroid disease and required surgery. Some types of parabens were detected in these samples, such as MP, EP, and PP. | MP and EP were found in urine samples in 99.06%, 95.29%, and 92%, respectively. There was a ↑ concentration of all parabens in the urine of both the nodule and cancer groups. MP and EP were associated with a benign nodule, especially when in higher concentrations. All three parabens studied were associated with an increased risk of thyroid cancer, with EP having the greatest association. | [96] |
| Mother—children | Urine samples from mothers of newborns were collected on the day of delivery. The concentrations of 5 parabens were determined by chromatography. Umbilical cord blood was collected immediately after birth, in which tT3, tT4, fT3, fT4, TSH, anti-TPO, and anti-TG were measured. | MP and EP were detected in the urine of the evaluated mothers. EP was positively related to increased tT3 in the umbilical cord and to anti-TPO. EP was correlated with increased birth weight in boys, but not in girls. | [72] |
| Human—Korea | Population study with 1254 people from Korea. Urine samples from this population were collected for analysis of the presence of EDC. Blood serum samples were also collected for measurement of tT4 and fT4, tT3 and fT3, TSH, anti-TPO, anti-thyroglobulin, thyroxine-binding globulin (TBG), and iodothyronine deiodinase (DIO) activity. | Parabens were found in most of the studied population (more than 90%). MP showed a positive association with altered levels of tT3. The increase in MP and EP parabens was correlated with an increase in TBG. | [59] |
| Pregnant women—Puerto Rico | Urine collection at 3 different gestational moments (16–20, 20–24, 24–28 weeks of gestation). | MP was associated with a decrease in SHBG. MP leads to a significant decrease in TSH and a decrease in the T3/T4 ratio particularly at weeks 24–28 of gestation. | [90] |
| Pregnant women—California | Urine and blood collection in the second gestational trimester and blood collection from neonates for measurement of tT4 and TSH. | MP was inversely associated with TSH levels with no changes in tT4 levels. | [95] |
| Pregnant women—Puerto Rico | Urine and blood collection at 4 time points during pregnancy. Parabens were detected in urine by chromatography. In the blood, tT4, fT4, TSH, and T3 were measured. | Urine samples that tested positive for the presence of MP were associated with increased T3 and negatively associated with fT4 at gestational age less than 21 weeks. | [89] |
| Pregnant women (12–14 weeks) |
Urine collection at 3 different gestational moments (16–20, 20–24, 24–28 gestation weeks) and hormone analyses. | MP (293 ng/mL) was associated with a 7.70% increase in SHBG. | [98] |
| Human | Urine samples from a representative portion of the US population to assess urinary concentrations of triclosan and parabens. | Inverse associations have been found between parabens and circulating levels of thyroid hormones in adults, where women appear to be more vulnerable to exposure. | [99] |
| Mother–children | Maternal blood was collected during the first prenatal care visit for TSH measurement. MP was detected in meconium samples from newborns. | MP exposure leads to a decrease in gestational age, a significant change in newborn weight, and a decrease in maternal TSH levels. In addition, MP in meconium was associated with about a 16% decrease in tT3 and a decrease in fT4. MP may influence maternal thyroid physiology during pregnancy, and this may lead to the development of ADHD. | [81] |
| Mother–twin pairs | MP was extracted from urine samples of pregnant women using liquid-liquid extraction. Neonatal TSH levels were abstracted from medical records in China. | MP exposure in early pregnancy was associated with an increased intra-twin TSH difference. | [100] |
| Wistar rats | Oral exposure for 90 days to BPA (50 mg/kg) or BPA+MP (250 mg/kg). | A minimal thyroid receptor antagonistic effect was only observed after treatment with BPA+MP. MP demonstrated antioxidant properties by reducing lipid peroxidation and generation of hydroxyl radicals induced by exposure to BPA. | [101] |
| Zebrafish larvae | Larvae were exposed to the following concentrations: 0, 20, 50, and 100 μM of EP and 0, 20, 100, and 200 μM of MP. | Serum T3 concentrations decreased at most concentrations tested (EP at 50, 100 μM and MP at 20, 100, and 200 μM) and T4 concentrations decreased at all concentrations tested. | [92] |