[Study on constructing the U-shaped response relationship of urinary iodine level and thyroid nodule prevalence based on piecewise function quantile regression method].

To establish an asymmetric U-shaped response relationship between urinary iodine level and thyroid nodule prevalence. Taking "Iodine" "Urine Iodine" "Thyroid" and "Thyroid Nodule" as Chinese keywords, and "Urine Iodine" "Goiter" and "Thyroid Nodule" as English keywords, literatures about urine iodine level and thyroid nodule prevalence were searched in China Biology Medicine disc, China National Knowledge Internet, Wanfang Data, PubMed and Springer databases from January 2000 to December 2019 respectively. The language of literatures was restricted in Chinese and English. There were 46 articles (24 domestic and 22 foreign) included in the study. The quantile regression method and Sigmoid function model were used to fit the dose-response relationship between different levels of urinary iodine and thyroid nodule prevalence to estimate the prevalence of thyroid nodule in Chinese residents. The fitted dose-response curves between different levels of urine iodine, ranging from low level to appropriate level and then to high level, and thyroid nodule prevalence had a good performance on the simulation of the asymmetric U-shaped relationship between urine iodine level and thyroid nodule prevalence. The median level of urinary iodine at the cut-off point of the piecewise function was 198 μg/L. Based on the weighted calculation of the total sample size included in the literature, the prevalence of thyroid nodules (95%) in Chinese residents was 23.0% (17.3%-30.7%). The asymmetric U-shaped response relationship between urinary iodine level and thyroid nodule prevalence based on piecewise function has good feasibility and fitting effect.