Synergism between exposure to mercury and use of iodine supplements on thyroid hormones in pregnant women.
OBJECTIVE
To evaluate the association between mercury exposure and thyroid-stimulating hormone (TSH), total triiodothyronine (TT3) and free thyroxine (FT4) levels during pregnancy as well as to explore if there is any synergic action between mercury and intake of iodine from different sources.


METHODS
The study population was 1407 pregnant women participating in the Spanish INMA birth cohort study. Total mercury concentrations were analyzed in cord blood. Thyroid hormones (THs) were measured in serum samples collected at 13.2±1.5 weeks of gestation. The association between mercury and TH levels was evaluated with multivariate linear regression models. Effect modification caused by iodine intake from supplements and diet was also evaluated.


RESULTS
The geometric means of TSH, TT3, FT4 and mercury were 1.1μU/L, 2.4nmol/L, 10.5pmol/L and 7.7μg/L, respectively. Mercury levels were marginally significantly associated with TT3 (β: -0.05; 95%CI: -0.10, 0.01), but were neither associated with TSH nor FT4. The inverse association between mercury and TT3 levels was stronger among the iodine supplement consumers (-0.08; 95%CI: -0.15, -0.02, interaction p-value=0.07). The association with FT4 followed the same pattern, albeit not significant.


CONCLUSIONS
Prenatal mercury exposure was inversely associated with TT3 levels among women who took iodine supplements during pregnancy. These results could be of public health concern, although further research is needed.
FISABIO-Universitat de València-Universitat Jaume I Joint Research Unit of Epidemiology and Environmental Health, Av. Catalunya 21, 46020 Valencia, Spain; Spanish Consortium for Research on Epidemiology and Public Health (CIBERESP), Madrid, Spain. Electronic address: llop_sab@gva.es.
Sabrina
S
Llop
FISABIO-Universitat de València-Universitat Jaume I Joint Research Unit of Epidemiology and Environmental Health, Av. Catalunya 21, 46020 Valencia, Spain; Spanish Consortium for Research on Epidemiology and Public Health (CIBERESP), Madrid, Spain.
Maria-Jose
MJ
Lopez-Espinosa
FISABIO-Universitat de València-Universitat Jaume I Joint Research Unit of Epidemiology and Environmental Health, Av. Catalunya 21, 46020 Valencia, Spain; Spanish Consortium for Research on Epidemiology and Public Health (CIBERESP), Madrid, Spain.
Mario
M
Murcia
Spanish Consortium for Research on Epidemiology and Public Health (CIBERESP), Madrid, Spain; Centre for Research in Environmental Epidemiology (CREAL), Doctor Aiguader 88, 08003 Barcelona, Spain; Municipal Institute of Medical Research (IMIM-Hospital del Mar), Doctor Aiguader 88, 08003 Barcelona, Spain.
Mar
M
Alvarez-Pedrerol
Spanish Consortium for Research on Epidemiology and Public Health (CIBERESP), Madrid, Spain; Universidad Miguel Hernandez, Avenida de Alicante KM 87, 03550 Sant Joan d´Alacant, Spain.
Jesús
J
Vioque
Laboratorio de Salud Pública de Alava, Santiago 11, 01002 Vitoria Gasteiz, Spain.
Xabier
X
Aguinagalde
Spanish Consortium for Research on Epidemiology and Public Health (CIBERESP), Madrid, Spain; Centre for Research in Environmental Epidemiology (CREAL), Doctor Aiguader 88, 08003 Barcelona, Spain; Municipal Institute of Medical Research (IMIM-Hospital del Mar), Doctor Aiguader 88, 08003 Barcelona, Spain.
Jordi
J
Julvez
Departamento de Sanidad Gobierno Vasco, Subdirección de Salud Pública de Gipuzkoa, Avenida de Navarra 4, 20013 San Sebastián, Spain; Biodonostia, Instituto de Investigación Biomédica, Doctor Begiristain, s/n, 20014 San Sebastián, Spain; Departamento de Medicina Preventiva y Salud Pública, University of the Basque Country (UPV/EHU), Apartado 1599, 20014 San Sebastian, Spain.
Juan J
JJ
Aurrekoetxea
Laboratorio de Salud Pública de Bizkaia, Departamento de Salud del Gobierno Vasco, Parque Tecnológico de Bizkaia, C/Ibaizabal, Edificio 502, 1ª Pt, 48160 Derio, Spain.
Mercedes
M
Espada
Spanish Consortium for Research on Epidemiology and Public Health (CIBERESP), Madrid, Spain; Departamento de Sanidad Gobierno Vasco, Subdirección de Salud Pública de Gipuzkoa, Avenida de Navarra 4, 20013 San Sebastián, Spain; Biodonostia, Instituto de Investigación Biomédica, Doctor Begiristain, s/n, 20014 San Sebastián, Spain.
Loreto
L
Santa-Marina
FISABIO-Universitat de València-Universitat Jaume I Joint Research Unit of Epidemiology and Environmental Health, Av. Catalunya 21, 46020 Valencia, Spain; Spanish Consortium for Research on Epidemiology and Public Health (CIBERESP), Madrid, Spain; Universitat Jaume I, Av. de Vicent Sos Baynat, s/n, 12071 Castelló de la Plana, Spain.
Marisa
M
Rebagliato
FISABIO-Universitat de València-Universitat Jaume I Joint Research Unit of Epidemiology and Environmental Health, Av. Catalunya 21, 46020 Valencia, Spain; Spanish Consortium for Research on Epidemiology and Public Health (CIBERESP), Madrid, Spain.
Ferran
F
Ballester
D065966:Absorption, Physicochemical / Q000187:drug effects; D000328:Adult; D015331:Cohort Studies; D019587:Dietary Supplements; D004781:Environmental Exposure; D004784:Environmental Monitoring; D005260:Female; D005312:Fetal Blood / Q000737:chemistry; D015200:Fluoroimmunoassay; D006801:Humans; D007455:Iodine / Q000494:pharmacology*; D008628:Mercury / Q000097:blood*; D011247:Pregnancy; D013030:Spain; D013054:Spectrophotometry, Atomic; D013972:Thyrotropin / Q000097:blood*; D013974:Thyroxine / Q000097:blood*; D014284:Triiodothyronine / Q000097:blood*
D014284:Triiodothyronine; D013972:Thyrotropin; D007455:Iodine; D008628:Mercury; D013974:Thyroxine
Endocrine disruption; Iodine supplementation; Mercury; Prenatal exposure; Thyroid