Age and Gender Specific Thyroid Hormones and Their Relationships with Body Mass Index in a Large Chinese Population: A Clinical Trial

Abstract

Objectives To investigate the associations of thyroid-stimulating hormone (TSH), free triiodothyronine (FT3) and free thyroxine (FT4) with body mass index (BMI) and the effect of age and gender on these relationships in a large Chinese population. Methods A total of 97,997 individuals from a health examination center were selected. The medians (25th and 75th) of TSH, FT3 and FT4 were used to explore the trends based on gender, 10-year age groups and BMI. The relationships of TSH, FT3 and FT4 with BMI were assessed by generalized additive models (GAM) along with adjusting the effect of age and gender. Results After applying our exclusion criteria, 77,991 euthyroid participants (45,428 males and 32,563 females) were analyzed. The medians of TSH level based on BMI groups were significantly higher in female participants than those in males in all age groups (P < 0.05), and the median FT3 level was lower in female subjects; however, there was no significant difference between male and female subjects in median FT4 level. The GAM analysis showed the non-linear positive association of TSH and FT3 with BMI, and these relationships were markedly influenced by age and gender. However, FT4 had a negative relationship with BMI, with neglectable effect of age and gender. Conclusions TSH, FT3 and BMI have a non-linear and positive quadratic relationship after age and gender adjustment. FT4, however, has a negative non-linear relationship with BMI with neglectable influence of age and gender.

Environmental Factors Affecting Thyroid-Stimulating Hormone and Thyroid Hormone Levels

“…Genetic factors account for up to 65% of interindividual variations in TSH and thyroid hormone levels [ 6 , 7 ], but many other factors can also influence thyroid function. Such factors include demographic factors (age and sex [ 8 , 9 ]), intrinsic factors (microbiota [ 10 ], stress [ 11 ]), usage of medicaments [ 12 ] and various environmental factors [ 13 , 14 , 15 , 16 ]. The purpose of this review is to provide a comprehensive insight into the literature discussing the impact of environmental factors (such as lifestyle factors and pollutants) on TSH and thyroid hormone levels ( Figure 1 ).…”

Free Thyroxine Levels are Associated with Cold Induced Thermogenesis in Healthy Euthyroid Individuals

“…by systematic mild cold exposure, has been demonstrated to improve insulin sensitivity (16) and reduce body fat mass (42). In line with these findings, large cohort studies in China and Belgium demonstrated favorable effects of higher levels of thyroxine within the reference range, in euthyroid individuals (11,30), which might be facilitated in part by CIT.…”

“…However, the consequences of subtle changes in thyroid hormone levels on metabolism are less certain. Several cross-sectional studies suggest that variations of free thyroxine (free T4) and free triiodothyronine (free T3) within the reference range are associated with metabolic health (8)(9)(10)(11). In mammals, TH is crucial for the maintenance of body core temperature by positively regulating thermogenesis (12).…”

Study on the independent effect of thyroid hormone based on uric acid level on NAFLD

“…Thyroid hormones T3 and T4 are synthesized in the thyroid gland and are associated with thyroglobulin [ 8 ]. Some researchers proposed that TSH, FT3, and BMI presented a nonlinear positive quadratic relationship, while FT4 and BMI presented a negative nonlinear relationship [ 9 ]. It has also been found that obese children can significantly improve the structure and function of the thyroid gland after weight loss [ 10 ].…”