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

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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.

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Most cited references 46

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Iodine deficiency and thyroid disorders.

Michael Zimmermann, Kristien Boelaert (2015)

Iodine deficiency early in life impairs cognition and growth, but iodine status is also a key determinant of thyroid disorders in adults. Severe iodine deficiency causes goitre and hypothyroidism because, despite an increase in thyroid activity to maximise iodine uptake and recycling in this setting, iodine concentrations are still too low to enable production of thyroid hormone. In mild-to-moderate iodine deficiency, increased thyroid activity can compensate for low iodine intake and maintain euthyroidism in most individuals, but at a price: chronic thyroid stimulation results in an increase in the prevalence of toxic nodular goitre and hyperthyroidism in populations. This high prevalence of nodular autonomy usually results in a further increase in the prevalence of hyperthyroidism if iodine intake is subsequently increased by salt iodisation. However, this increase is transient because iodine sufficiency normalises thyroid activity which, in the long term, reduces nodular autonomy. Increased iodine intake in an iodine-deficient population is associated with a small increase in the prevalence of subclinical hypothyroidism and thyroid autoimmunity; whether these increases are also transient is unclear. Variations in population iodine intake do not affect risk for Graves' disease or thyroid cancer, but correction of iodine deficiency might shift thyroid cancer subtypes toward less malignant forms. Thus, optimisation of population iodine intake is an important component of preventive health care to reduce the prevalence of thyroid disorders.

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Bias in dietary-report instruments and its implications for nutritional epidemiology.

Elio Riboli, Pietro Ferrari, Peter R. Carroll … (2002)

To evaluate measurement error structure in dietary assessment instruments and to investigate its implications for nutritional studies, using urinary nitrogen excretion as a reference biomarker for protein intake. The dietary assessment methods included different food-frequency questionnaires (FFQs) and such conventional dietary-report reference instruments as a series of 24-hour recalls, 4-day weighed food records or 7-day diaries. Six original pilot validation studies within the European Prospective Investigation of Cancer (EPIC), and two validation studies conducted by the British Medical Research Council (MRC) within the Norfolk cohort that later joined as a collaborative component cohort of EPIC. A sample of approximately 100 to 200 women and men, aged 35-74 years, from each of eight validation studies. In assessing protein intake, all conventional dietary-report reference methods violated the critical requirements for a valid reference instrument for evaluating, and adjusting for, dietary measurement error in an FFQ. They displayed systematic bias that depended partly on true intake and partly was person-specific, correlated with person-specific bias in the FFQ. Using the dietary-report methods as reference instruments produced substantial overestimation (up to 230%) of the FFQ correlation with true usual intake and serious underestimation (up to 240%) of the degree of attenuation of FFQ-based log relative risks. The impact of measurement error in dietary assessment instruments on the design, analysis and interpretation of nutritional studies may be much greater than has been previously estimated, at least regarding protein intake.

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Association between screening and the thyroid cancer “epidemic” in South Korea: evidence from a nationwide study

Sohee Park, Chang-Mo Oh, Hyunsoon Cho … (2016)

Objective To investigate whether screening for thyroid cancer led to the current “epidemic” in South Korea. Design Review of the medical records of nationally representative samples of patients with a diagnosis of thyroid cancer in 1999, 2005, and 2008. Setting Sample cases were randomly selected from South Korea’s nationwide cancer registry, using a systematic sampling method after stratification by region. Participants 5796 patients with thyroid cancer were included (891 in 1999, 2355 in 2005, and 2550 in 2008). Main outcome measures The primary outcome was age standardised incidence of thyroid cancer and the changes in incidence between 1999 and 2008 according to the methods used to detect tumours (screen detection versus clinical detection versus unspecified). Results Between 1999 and 2008, the incidence of thyroid cancer increased 6.4-fold (95% confidence interval 4.9-fold to 8.4-fold), from 6.4 (95% confidence interval 6.2 to 6.6) per 100 000 population to 40.7 (40.2 to 41.2) per 100 000 population. Of the increase, 94.4% (34.4 per 100 000 population) were for tumours less than 20 mm, which were detected mainly by screening. 97.1% of the total increase was localised and regional tumours according to the Surveillance, Epidemiology, and End Results (SEER) summary stage. Where cases were clinically detected, 99.9% of the increased incidences (6.4 per 100 000 population) over the same period were tumours less than 20 mm. Conclusion The current “epidemic” of thyroid cancer in South Korea is due to an increase in the detection of small tumours, most likely as a result of overdetection. Concerted efforts are needed at a national level to reduce unnecessary thyroid ultrasound examinations in the asymptomatic general population.

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Author and article information

Journal

Journal ID (nlm-ta): Endocrinol Metab (Seoul)

Journal ID (iso-abbrev): Endocrinol Metab (Seoul)

Title: Endocrinology and Metabolism

Publisher: Korean Endocrine Society

ISSN (Print): 2093-596X

ISSN (Electronic): 2093-5978

Publication date (Print): August 2021

Publication date (Electronic): 11 August 2021

Volume: 36

Issue: 4

Pages: 790-799

Affiliations

[1 ]Department of Preventive Medicine, Seoul National University College of Medicine, Seoul, Korea

[2 ]Department of Biomedical Science, Seoul National University Graduate School, Seoul, Korea

[3 ]Cancer Research Institute, Seoul National University, Seoul, Korea

[4 ]Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea

[5 ]Department of Molecular Medicine and Biopharmaceutical Sciences, Graduate School of Convergence Science and Technology, Seoul National University, Seoul, Korea

[6 ]Department of Surgery, Seoul National University Hospital, Seoul National University College of Medicine, Seoul, Korea

[7 ]Division of Surgery, Thyroid Center, Seoul National University Cancer Hospital, Seoul, Korea

[8 ]Integrated Major in Innovative Medical Science, Seoul National University College of Medicine, Seoul, Korea

[9 ]Department of Family Medicine, Dongguk University College of Medicine, Gyeongju, Korea

Author notes

Corresponding author: Sue K. Park, Department of Preventive Medicine, Seoul National University College of Medicine, 103 Daehak-ro, Jongno-gu, Seoul 03080, Korea, Tel: +82-2-740-8338, Fax: +82-2-747-4830, E-mail: suepark@ 123456snu.ac.kr

Author information

Kyungsik Kim https://orcid.org/0000-0001-9007-7025

Sue K. Park https://orcid.org/0000-0001-5002-9707

Article

Publisher ID: enm-2021-1034

DOI: 10.3803/EnM.2021.1034

PMC ID: 8419609

PubMed ID: 34376043

SO-VID: bfbf14a1-9f4f-4f6f-978f-f1bb0b54f8da

License:

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( https://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

History

Date received : 13 March 2021

Date revision received : 28 June 2021

Date accepted : 2 July 2021

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

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Most cited references 46

Iodine deficiency and thyroid disorders.

Bias in dietary-report instruments and its implications for nutritional epidemiology.

Association between screening and the thyroid cancer “epidemic” in South Korea: evidence from a nationwide study

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