Abstract
BACKGROUND: Previous studies have revealed the sex-specific features of pituitary-thyroid hormone (TH) actions and the prevalence of thyroid nodules (TNs) in children and adolescents. However, it was unclear in adults. We aimed to investigate the features of pituitary-TH actions in women and men at different ages, and the associations of thyrotropin (TSH), THs, and central sensitivity to THs indices including the thyroid feedback quantile-based index by FT4 (TFQI(FT4)) and the thyroid feedback quantile-based index by FT3(TFQI(FT3)) with of TNs in Chinese euthyroid adults. METHODS: 8771 euthyroid adults from the communities in China were involved. Demographic, behavioral, and anthropometric data were gathered through the questionnaires. Ultrasound was performed to evaluate the TNs. TSH and THs levels were measured. The multivariable logistic regression and multivariable ordinal logistic regression were conducted. RESULTS: TFQI(FT3) among both genders, except women aged 43 to 59 years, where it increased slightly. Additionally, there was an age-related decline in TFQI(FT4) levels in both women and men at ages < 50 and < 53, respectively, but a marked increase after that. Lower TSH levels were significantly associated with a higher prevalence and lower odds of having fewer TNs using multiple nodules as the base category in both men and women (both P for trend < 0.05). Additionally, lower TFQI(FT3) and TFQI(FT4) levels were significantly associated with a higher prevalence of TNs in women (both P for trend < 0.05), and lower TFQI(FT3) levels were significantly associated with a higher prevalence of TNs in men. Both higher TFQI(FT3) and TFQI(FT4) levels were significantly associated with higher odds of having fewer TNs using multiple nodules as the base category in women. However, the relationships between TFQI(FT4) and the prevalence or number of TNs in men were not found. CONCLUSIONS: The trends of THs, TSH, TFQI(FT4), and TFQI(FT3) at different ages were sex-dependent. Both TFQI(FT4) and TFQI(FT3) levels were negatively associated with the prevalence and number of TNs in women. The present results may lead to a better understanding of the sex-specific relationships between the development of the pituitary-TH axis and the formation of TNs.