Korean J Fam Pract 2020; 10(1): 3-8  https://doi.org/10.21215/kjfp.2020.10.1.3
Relationship between Shift Work and Subclinical Hypothyroidism
Hye-a Hwang, Young-jee Jeon*
Department of Family Medicine, Ulsan University Hospital, University of Ulsan College of Medicine, Ulsan, Korea
Young-jee Jeon
Tel: +82-52-250-8847, Fax: +82-52-250-8330
E-mail: yjjeon@uuh.ulsan.kr
ORCID: http://orcid.org/0000-0002-8070-2453
Received: October 1, 2019; Revised: December 19, 2019; Accepted: December 19, 2019; Published online: February 20, 2020.
© The Korean Academy of Family Medicine. All rights reserved.

This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract
Background: To date, only a few studies have reported the relationship between shift work and subclinical hypothyroidism. Therefore, this study aimed to investigate this relationship. Subclinical hypothyroidism is defined as normal thyroxine (free T4) and thyrotropin (thyroid stimulating hormone, TSH) levels above 10 mU/L.
Methods: This study included 12,126 male participants who visited Ulsan University Hospital health promotion center from March 1, 2016 to February 28, 2017. Participants answered a self-administered survey about their marital status, educational level, smoking habits, alcohol intake, and frequency of physical activity. Venous blood sampling was performed after maintaining fasting state for at least 8 hours to test for fasting glucose, hemoglobin A1c, total cholesterol, TSH, and free T4.
Results: The TSH level was significantly higher in shift workers than that in the non-shift workers, whereas free T4 level did not show any difference between the two groups. In the shift work group, the odds ratio for subclinical hypothyroidism was significantly higher (odds ratio, 1.99, 95%; confidence interval, 1.16–3.40). This result persisted after adjusting for covariates of age, body mass index, educational level, smoking habits, alcohol intake, and frequency of physical activity.
Conclusion: The odds of subclinical hypothyroidism were higher in the shift work group. Therefore, clinicians should pay more attention to detect subclinical hypothyroidism in shift workers.
Keywords: Shift Work Schedule; Occupational Groups; Thyroid Disease; Hypothyroidism
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