1 Endocrine Research Center, Research Institute for Endocrine Sciences, Shahid Beheshti University of Medical Sciences , Tehran, Iran .
2 Department of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences , Tehran, Iran .
Thyroid. 2018 Apr;28(4):458-464. doi: 10.1089/thy.2017.0454. Epub 2018 Apr 5.
Considering inconsistent and conflicting data on associations of thyroid function, within the reference range, with anthropometric measures and metabolic syndrome, this study aimed to investigate the relationship between thyroid function and different obesity phenotypes over nine years of follow-up.
This study was conducted on 1938 individuals from an ongoing population-based cohort study, the Tehran Thyroid Study. Participants were categorized into four obesity phenotypes based on body mass index and metabolic status. To investigate the associations of thyrotropin and free thyroxine (fT4) with incidence of different obesity phenotypes across the study period, a multivariate approach based on a generalized estimating equation method was used.
At baseline, individuals with the metabolically healthy normal weight (MHNW) phenotype had higher serum fT4 levels (1.2 ± 0.16 ng/dL vs. 1.14 ± 0.14 ng/dL, 1.16 ± 0.14 ng/dL, and 1.17 ± 0.15 ng/dL in metabolically healthy obese [MHO], metabolically unhealthy normal weight, and metabolically unhealthy obese individuals, respectively). The results of the generalized estimating equation analysis after multivariate adjustment for age, sex, smoking, physical activity, education level, thyroid peroxidase antibody status, and homeostasis model assessment-insulin resistance showed that each 1 ng/dL increment in fT4 levels within the reference range was accompanied with a 1.65-fold [confidence interval (CI) 1.09-2.5] increase of developing the MHNW phenotype during 9.2 years of follow-up. Moreover, each 1.0 ng/dL increment in fT4 within the reference range was associated with a 50% decreased risk of developing the MHO phenotype (odds ratio = 0.50 [CI 0.32-0.76]). Meanwhile, a significant positive association was found between serum thyrotropin levels and development of the metabolically unhealthy normal weight phenotype (odds ratio = 1.22 [CI 1.01-1.48]).
Serum fT4 concentrations within the reference range are associated with the development of some obesity phenotypes, including the MHNW and MHO phenotypes, after consideration of potential confounders.
考虑到甲状腺功能在参考范围内与人体测量指标和代谢综合征的关联存在不一致和相互矛盾的数据，本研究旨在调查甲状腺功能与九年随访期间不同肥胖表型之间的关系。
本研究基于一项正在进行的基于人群的队列研究，即德黑兰甲状腺研究，对 1938 名个体进行了研究。参与者根据体重指数和代谢状态分为四种肥胖表型。为了研究促甲状腺激素和游离甲状腺素（fT4）与研究期间不同肥胖表型发生率的关系，采用了基于广义估计方程方法的多变量方法。
在基线时，具有代谢健康正常体重（MHNW）表型的个体具有更高的血清 fT4 水平（1.2±0.16ng/dL 与 1.14±0.14ng/dL、1.16±0.14ng/dL 和 1.17±0.15ng/dL 分别在代谢健康肥胖 [MHO]、代谢不健康正常体重和代谢不健康肥胖个体中）。经过多变量调整年龄、性别、吸烟、体力活动、教育水平、甲状腺过氧化物酶抗体状态和稳态模型评估胰岛素抵抗后，广义估计方程分析的结果表明，在参考范围内，fT4 水平每增加 1ng/dL，在 9.2 年的随访期间，发展为 MHNW 表型的风险增加 1.65 倍（95%置信区间为 1.09-2.5）。此外，在参考范围内 fT4 每增加 1.0ng/dL，发展为 MHO 表型的风险降低 50%（比值比=0.50 [95%置信区间 0.32-0.76]）。同时，血清促甲状腺激素水平与代谢不健康正常体重表型的发展呈显著正相关（比值比=1.22 [95%置信区间 1.01-1.48]）。
在考虑潜在混杂因素后，参考范围内的血清 fT4 浓度与一些肥胖表型的发展有关，包括 MHNW 和 MHO 表型。
