A Higher Ratio of Estradiol to Testosterone Is Associated with Autoimmune Thyroid Disease in Males

Background: Autoimmune thyroid disease (AITD) is highly prevalent. Although AITD is less common in males, it is unclear whether estradiol (E 2 ) combined with total testosterone (T) contributes to the prevalence of AITD. This study evaluated the association between the E 2 /T ratio and the prevalence of AITD in males. Methods: The data were obtained from a cross-sectional population-based study, the SPECT-China study, 2014–2015. A total of 4109 males ≥18 years of age were enrolled in this study. Participants underwent several checkups, which included assays of serum E 2 , T, thyroid peroxidase antibody (TPOAb), and thyroglobulin antibody (TgAb) levels, as well as thyroid ultrasonography (US). AITD was defined based on the presence of TPOAb and TgAb levels, and the presence of thyroid US findings. Results: Overall, the prevalence of positivity for TPOAb and/or TgAb (TPO/TgAb[+]) was 11.02%, and the positivity for TPOAb and/or TgAb together with US (TPO/TgAb[+] and US[+]) was 4.58%. The E 2 /T ratio levels were significantly higher in the TPO/TgAb(+) group and the TPO/TgAb(+) and US(+) group (7.91 ± 8.03 vs. 7.19 ± 10.30, p = 0.003; 8.78 ± 11.26 vs. 7.19 ± 10.30, p = 0.001) compared to the TPO and TgAb(–) group. The prevalence of TPO/TgAb(+) and US(+) significantly increased with an increasing E 2 /T ratio ( p = 0.013). Binary logistic analysis showed that increased E 2 /T ratio levels were associated with an increased risk of AITD (TPO/TgAb[+]: odds ratio = 1.35, p = 0.002; TPO/TgAb[+] and US[+]: odds ratio = 1.48, p = 0.006). Conclusions: AITD is highly prevalent in males in China. Higher E 2 /T ratios were significantly associated with AITD among males. Further studies will be needed to assess whether there is a causal relationship between E 2 /T ratios and AITD.