Relationship of gender and age on thyroid hormone parameters in a large Chinese population

ABSTRACT Objective This study aimed to present the impact of age and gender on thyroid hormone levels in a large Chinese population with sufficient iodine intake. Subjects and methods A total of 83643 individuals were included and were stratified by age and gender. The median, 2.5th and 97.5th of thyrotropin (TSH), free triiodothyronine (FT3), free thyroxine (FT4) and FT3/FT4 ratio were calculated for both genders for every decade from 18 to over 80 years. TSH, FT3, FT4, FT3/FT4 distribution in each age group was evaluated for females and males using smoothing splines in the generalized additive models (GAM). TSH concentrations were compared in the different age groups in gender. Results In the over 80s age group, the TSH level (median: 2.57 mIU/L, 2.5th-97.5th: 0.86-7.56 mIU/L) was significantly higher than other age groups, irrespective to gender (P<0.001). Females had a higher TSH value than males in all age groups (P<0.001). Results of the smoothing curves showed that TSH increased with age, FT3 concentration was higher in males than in females and the tendency of the FT3/FT4 ratio was basically similar to that of FT3. TSH concentration in the 50s age group (median 2.48 mIU/L for females versus 2.00 mIU/L for males) was significantly higher than that in the 30s age group (median 2.18 mIU/L for females versus median 1.85 mIU/L for males). Conclusions In accord with increasing TSH values during aging, females and older adults have lower FT3 values and lower FT3/FT4 ratios, while the FT4 values remain stable.

摘要
研究目的：本研究旨在阐明碘摄入充足的中国大样本人群中，年龄与性别对甲状腺激素水平的影响。
研究对象与方法：本研究共纳入83643名研究对象，按年龄与性别进行分层。针对18岁至80岁以上的每一个十年年龄段，分别计算不同性别人群的促甲状腺素（thyrotropin, TSH）、游离三碘甲状腺原氨酸（free triiodothyronine, FT3）、游离甲状腺素（free thyroxine, FT4）及FT3/FT4比值的中位数、2.5分位数与97.5分位数。采用广义加性模型（generalized additive models, GAM）中的平滑样条方法，评估不同年龄组男女的TSH、FT3、FT4及FT3/FT4比值的分布特征，并比较不同年龄组间男女的TSH浓度差异。
研究结果：无论性别，80岁以上人群的TSH水平（中位数：2.57 mIU/L，2.5~97.5百分位区间：0.86~7.56 mIU/L）均显著高于其他年龄组（P<0.001）。各年龄组女性的TSH值均高于男性（P<0.001）。平滑曲线分析结果显示，TSH水平随年龄增长而升高；男性FT3浓度高于女性，且FT3/FT4比值的变化趋势与FT3基本一致。50岁年龄组的TSH浓度（女性中位数2.48 mIU/L，男性中位数2.00 mIU/L）显著高于30岁年龄组（女性中位数2.18 mIU/L，男性中位数1.85 mIU/L）。
研究结论：本研究结果与TSH水平随年龄增长而升高的结论一致，女性及老年人群的FT3值与FT3/FT4比值均较低，而FT4水平保持稳定。