Introduction: Although autoimmune thyroid disease is less common in males, it is unclear whether estrogen contributes to the difference in susceptibility among males.
Objective: To examine whether circulating estradiol (E₂) is related to thyroid autoimmunity in males.
Patients and methods: One-thousand two-hundred and sixty-three males aged 15-94 years were studied. Serum levels of E₂, TSH receptor antibody (TRAb), thyroid peroxidase antibody (TPOAb), thyroglobulin antibody (TgAb), free thyroxine (FT₄), and TSH were measured by ELISA.
Results: Circulating E₂ varied widely in males, ranging 18.4-403.7 pmol/l with a mean value of 136.2±51.7 pmol/l. E₂ increased with age (r=0.18, P<0.001). No relationship between E₂ and BMI was found. When comparing the difference in E₂ according to the test results of TRAb, TPOAb, and TgAb, it was found that E₂ was significantly higher in subjects with positive TRAb (TRAb positive, E₂=170.3±59.8 pmol/l; TRAb negative, E₂=134.0±50.6 pmol/l; P<0.001). No difference in E₂ was demonstrated according to the results of TPOAb or TgAb. Logistic regression analysis showed that E₂ was a determinant of positive TRAb, independent of age and BMI. There was no relationship between serum E₂ and TSH or FT₄. However, E₂ was negatively related to TSH (r=-0.45, P<0.01) in subjects whose TSH levels fell below the reference range (0.3-4.2 mIU/l).
Conclusion: Higher circulating E₂ is related to thyroid autoimmunity in males as reflected by positive TRAb.