Table 3.

Effects of benzylparaben, isopropylparaben, isobutylparaben, and propylparaben on thyroid function.

Model	Exposure/Dose/Analyses	Main Results	References
Female Sprague Dawley rats	Oral exposure to MP, EP, PP, isopropylparaben (IPP), BuP, and isobutylparaben (IBP) (62.5; 250 and 1000 mg/kg/day) from the 21st to the 40th postnatal day.	PP and IPP were associated with ↓ T4 and estradiol and changes in thyroid weight.	[93]
Male and female Sprague Dawley rats	Injections of IPP, IBP, or mixture of IPP and IBP at 50, 100, 300, and 600 mg/kg bw dissolved in 100 mL of ethanol (99%), 5 days per week for 28 days.	The mixture of IPP and IBP induces a decrease of TSH in exposed individuals at an exposure of 600 mg/kg bw.	[94]
Pregnant women (PROTECT)	Blood collection at two different gestational moments for measurement of SHBG, TSH, fT3, fT4, and progesterone/estradiol ratio; urine collection for detection of phenols and parabens by high-performance liquid chromatography (HPLC).	↑ estradiol and progesterone at the last visit; ↓ fT3 and fT4 at the last visit with no changes in TSH levels.	[88]
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.	PP was inversely associated with fT4.	[89]
Pregnant women—California	Urine and blood collection in the second gestational trimester and blood collection from neonates for measurement of tT4 and TSH.	PP was inversely associated with TSH levels with no changes in tT4 levels.	[95]
Pregnant women—Puerto Rico	Urine collection at 3 different gestational moments (16–20, 20–24, 24–28 weeks of gestation).	Exposure to PP was associated with ↓ SHBG and T3/T4 ratio.	[90]
Human (population of Wuhan, China)	Urine collection and detection of MP, EP, and PP.	PP has been associated with an increased risk of thyroid cancer.	[96]
Newborn human	Newborn blood spots were collected as part of the neonatal screening program, TSH and tT4 were assessed using immunofluorescence.	BuP increased TSH and decreased T4 hormone levels have been demonstrated in newborns and women with less than 150 μg/L of iodine.	[97]
Amphibian tadpoles	Oral exposure to PP (0.05; 0.5 and 5 mg/L) for 14 days.	An increase in PP concentrations in water has been associated with an acute toxic effect.	[87]
Zebrafish larvae	Larvae were exposed to the following concentrations: 0, 5, 10, and 20 μM of PP.	Serum T3 and T4 concentrations decreased at all concentrations tested. In 10 and 20 μM groups, PP increases TSH gene expression.	[92]