Thyroid Function Changes and Pubertal Progress in Females: A Longitudinal Study in Iodine-Sufficient Areas of East China

BACKGROUND: The onset of puberty is influenced by thyroid function, and thyroid hormones (THs) fluctuate substantially during the period of pubertal development. However, it needs to be further clarified how THs change at specific puberty stages and how it influences pubertal development in girls. So far, longitudinal data from China are scarce. METHODS: A cohort study was conducted among girls during puberty in iodine-sufficient regions of East China between 2017 to 2019. Serum thyroid stimulating hormone (TSH), free triiodothyronine (FT3), and free thyroxine (FT4) were determined for each participant. Thyroid homeostasis structure parameters (THSPs), including the ratio of FT4 to FT3 (FT4/FT3), Jostel’s TSH index (TSHI), and thyroid feedback quantile-based index (TFQI), were calculated. Puberty category scores (PCS), calculated based on the Puberty Development Scale (PDS), was used to assess the stage of puberty. Girls were grouped into three categories according to PCS changes (△PCS) and six categories according puberty stage (B(P)F(P): pre-pubertal at both baseline and follow-up; B(P)F(L): pre-pubertal at baseline and late-pubertal at follow-up, respectively; B(P)F(T): pre-pubertal at baseline and post-pubertal at follow-up, respectively; B(L)F(L): late-pubertal at both baseline and follow-up; B(L)F(T): late-pubertal at baseline and post-pubertal at follow-up, respectively; B(T)F(T): post-pubertal at both baseline and follow-up). Multiple linear regression analyses were used to evaluate the associations of THs changes with pubertal progress. RESULTS: The levels of serum TSH and FT3 decreased while serum FT4 increased during the study period (P<0.001). In multiple linear regression analyses, after adjustment for covariables, FT3 decreased by an additional 0.24 pmol/L (95% CI: -0.47 to -0.01) in the higher △PCS group than the lower △PCS group. Compared with the B(L)F(L) group, the B(P)F(T) group showed an additional decline in FT3 (β= -0.39 pmol/L, 95%CI: -0.73 to -0.04), the B(T)F(T) group showed a lower decline in TSH (β=0.50 mU/L, 95% CI: 0.21 to 0.80) and a lower decline in TSHI (β=0.24, 95%CI: 0.06 to 0.41), respectively. There was no association of △FT4 or △TFQI with △PCS or the puberty pattern. CONCLUSIONS: Serum TSH and FT3 decreased while serum FT4 increased among girls during puberty. Both the initial stage and the velocity of pubertal development were related to thyroid hormone fluctuations.