The Correlation between Polybrominated Diphenyl Ethers (PBDEs) and Thyroid Hormones in the General Population: A Meta-Analysis

Objective
Certain epidemiological studies have suggested exposure to polybrominated diphenyl ethers (PBDEs) affect the production and secretion of thyroid hormones (TH); however, conflicting results have been reported in different studies. There is not a convincing conclusion about this debate to date.
Materials and Methods
To perform a meta-analysis determining if there are correlations between PBDEs exposure and the serum levels of TH. Medical and scientific literature databases were searched for articles that met the eligibility criteria. The included articles were assessed for methodological quality. The correlation coefficient values or regression coefficient values between PBDEs and thyroid stimulating hormone (TSH) or total thyroxine (TT4) from each article were used for analysis.
Data Synthesis
Sixteen articles were included in this meta-analysis. Pearson correlation coefficients (r) were directly collected or calculated from data given in the articles. Then, Fisher’s z transformation was performed to convert each correlation coefficient to an approximately normal distribution. For z values between PBDEs exposure and TSH levels, the pooled z value for 18 studies was 0.08 (95% CI: -0.06, 0.22), and indicated significant heterogeneity (I2 values = 90.7%). Subgroup analysis was performed based on the median values of serum PBDEs in each study, there was not significant heterogeneity in each of the four subgroups (I2 values <30%). In meta-analysis of z values between PBDEs exposure and the levels of TT4, the pooled z value for 11 studies was -0.02 (95% CI: -0.11, 0.08), and also indicated significant heterogeneity (I2 values = 57.6%). Similar subgroup analysis was done for the PBDEs exposures and the levels of TT4. No significant heterogeneity was shown in either of the two subgroups (I2 values = 0).
Conclusion
The findings in our meta-analysis indicate the effects of PBDEs on thyroid function may mainly depend on PBDEs exposure and their levels found in serum. The relationship between PBDEs exposure and changes in thyroid function seem to fit an approximate u-shaped curve. These predictions await further verification, namely a prospective longitudinal study.

研究目的：已有流行病学研究提示，多溴二苯醚（polybrominated diphenyl ethers, PBDEs）暴露会影响甲状腺激素（thyroid hormones, TH）的生成与分泌，但不同研究所得结果存在分歧，截至目前针对该争议尚无令人信服的结论。

材料与方法：本研究通过荟萃分析探讨多溴二苯醚暴露与血清甲状腺激素水平之间的相关性。检索医学与科学文献数据库，筛选符合纳入标准的研究文献，并对纳入文献进行方法学质量评价。提取各文献中多溴二苯醚与促甲状腺激素（thyroid stimulating hormone, TSH）或总甲状腺素（total thyroxine, TT4）相关的相关系数或回归系数用于后续分析。

数据合成：本荟萃分析共纳入16项研究。直接提取或根据文献提供的数据计算皮尔逊相关系数（Pearson correlation coefficients, r），随后通过费希尔z变换（Fisher’s z transformation）将各相关系数转换为近似正态分布。针对多溴二苯醚暴露与促甲状腺激素水平的相关性分析，共纳入18项研究，合并z值为0.08（95%置信区间：-0.06, 0.22），研究间存在显著异质性（I²=90.7%）。基于各研究中血清多溴二苯醚的中位数水平开展亚组分析，四个亚组均未显示显著异质性（I²<30%）。针对多溴二苯醚暴露与总甲状腺素水平的相关性分析，共纳入11项研究，合并z值为-0.02（95%置信区间：-0.11, 0.08），同样存在显著异质性（I²=57.6%）。针对该部分分析亦开展了类似的亚组分析，两个亚组均未显示显著异质性（I²=0）。

结论：本荟萃分析结果显示，多溴二苯醚对甲状腺功能的影响可能主要取决于其暴露水平及血清中检出的浓度。多溴二苯醚暴露与甲状腺功能改变之间的关系近似呈U型曲线，该结论尚需进一步的前瞻性纵向研究予以验证。