Lead and cadmium exposure, higher thyroid antibodies and thyroid dysfunction in Chinese women

Background: Exposure to lead(Pb) or cadmium(Cd) has been related to decreasing thyroxine in many previous studies. The underlying mechanisms have not been clarified. Heavy metal-induced thyroid autoimmunity in pregnant women has been found, despite having been rarely explored in the general population.

Objectives: We aimed to determine whether the blood levels of lead(BPb) or cadmium(BCd) related to the levels of sera antibodies to thyroid proteins and thyroid dysfunction in the general population.

Methods: Our study included 5628 Chinese adults and was based on the 2014 SPECT-China study. Thyroid dysfunction and subclinical thyroid dysfunction were defined by total triiodothyronine (TT3), total thyroxine(TT4) and thyroid stimulating hormone (TSH).Thyroid peroxidase antibody (TPOAb), thyroglobulin antibodies (TGAb), TT3, TT4, and TSH were measured by immunochemiluminometric assays. BPb and BCd levels were tested by atomic absorption spectrometry. Linear and logistic regression models were used to analyze the associations.

Results: After adjustment for age, body mass index, smoking status (men only) and drinking status, the natural log(ln) BPb was positively related to the lnTPOAb (B = 0.062, P < 0.05) and to the lnTSH (B = 0.047, P < 0.01) in women. The lnBCd in women was positively related to the lnTGAb (B = 0.046, P < 0.05). In the adjusted logistic regression models, the BCd of women was positively related to their hypothyroid status and TGAb tertiles. The ORs of women in the middle and higher TPOAb tertiles were 1.38 (P < 0.001) and 1.35 (P < 0.001) times greater for every ln-unit increase in BPb, respectively. In men, no continuous correlation was found among variables.

Conclusions: In women, BPb and BCd levels were related to higher TSH and hypothyroid status, respectively, suggesting a Pb and Cd induction of sex-biased thyroid autoimmunity.