Endocrinol Metab.  2021 Aug;36(4):790-799. 10.3803/EnM.2021.1034.

Association between Iodine Intake, Thyroid Function, and Papillary Thyroid Cancer: A Case-Control Study

Affiliations
  • 1Department of Preventive Medicine, Seoul National University College of Medicine, Seoul, Korea
  • 2Department of Biomedical Science, Seoul National University Graduate School, Seoul, Korea
  • 3Cancer Research Institute, Seoul National University, Seoul, Korea
  • 4Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea
  • 5Department of Molecular Medicine and Biopharmaceutical Sciences, Graduate School of Convergence Science and Technology, Seoul National University, Seoul, Korea
  • 6Department of Surgery, Seoul National University Hospital, Seoul National University College of Medicine, Seoul, Korea
  • 7Division of Surgery, Thyroid Center, Seoul National University Cancer Hospital, Seoul, Korea
  • 8Integrated Major in Innovative Medical Science, Seoul National University College of Medicine, Seoul, Korea
  • 9Department of Family Medicine, Dongguk University College of Medicine, Gyeongju, Korea

Abstract

Background
This study aimed to assess the effects of iodine intake, thyroid function, and their combined effect on the risk of papillary thyroid cancer (PTC) and papillary thyroid microcarcinoma (PTMC).
Methods
A case-control study was conducted including 500 community-based controls who had undergone a health check-up, and 446 overall PTC cases (209 PTC and 237 PTMC) from the Thyroid Cancer Longitudinal Study. Urinary iodine concentration (UIC), was used as an indicator of iodine intake, and serum for thyroid function. The risk of PTC and PTMC was estimated using unconditional logistic regression.
Results
Excessive iodine intake (UIC ≥220 μg/gCr) was associated with both PTC (odds ratio [OR], 18.13 95% confidence interval [CI], 8.87 to 37.04) and PTMC (OR, 8.02; 95% CI, 4.64 to 13.87), compared to adequate iodine intake (UIC, 85 to 219 μg/gCr). Free thyroxine (T4) levels ≥1.25 ng/dL were associated with PTC (OR, 1.97; 95% CI, 1.36 to 2.87) and PTMC (OR, 2.98; 95% CI, 2.01 to 4.41), compared to free T4 levels of 0.7 to 1.24 ng/dL. Individuals with excessive iodine intake and high free T4 levels had a greatly increased OR of PTC (OR, 43.48; 95% CI, 12.63 to 149.62), and PTMC (OR, 26.96; 95% CI, 10.26 to 70.89), compared to individuals with adequate iodine intake and low free T4 levels.
Conclusion
Excessive iodine intake using creatinine-adjusted UIC and high free T4 levels may have a synergistic effect on PTC and PTMC. Considering both iodine intake and thyroid function is important to assess PTC and PTMC risk.

Keyword

Thyroid cancer, papillary; Papillary thyroid microcarcinoma; Iodine; Thyroid function tests
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