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Long working hours and the risk of hypothyroidism in healthy Korean workers: a cohort study
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Yesung Lee, Woncheol Lee, Hyoung-Ryoul Kim
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Epidemiol Health. 2022;44:e2022104. Published online November 8, 2022
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DOI: https://doi.org/10.4178/epih.e2022104
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Abstract
OBJECTIVES
Long working hours have been reported to cause various health problems, but are currently practiced in many countries. Building upon a previous cross-sectional study, the authors aimed to elucidate the causal relationship between long working hours and hypothyroidism through a longitudinal study.
METHODS Data were collected at baseline from 45,259 participants without thyroid disease and with consistent weekly working hours (36-40, 41-52, 53-60, and >60 hours) during the follow-up period. Hypothyroidism was defined using the reference limits of serum thyroid-stimulating hormone and free thyroxine levels. By estimating hazard ratios (HRs) and 95% confidence intervals (CIs) using Cox proportional hazards regression analysis, the risk of incident hypothyroidism was evaluated with 36-40 hours of work per week as the reference.
RESULTS During 138,261.7 person-years of follow-up, 2,914 participants developed hypothyroidism (incidence density, 2.11/102 person-years). The multivariable-adjusted HRs of incident hypothyroidism for 41-52 hours, 53-60 hours, and >60 hours of work per week were 1.13 (95% CI, 1.03 to 1.24), 2.53 (95% CI, 2.17 to 2.95), and 2.57 (95% CI, 2.09 to 3.15), respectively. In dose-response analyses, long working hours had an approximately linear relationship with hypothyroidism incidence. The risk of incident hypothyroidism in those who worked 53-60 hours and >60 hours per week compared with the reference group was significantly higher among the older age group (≥36 years, stratified by median age), men, and daytime workers.
CONCLUSIONS This large-scale cohort study demonstrated the association between long working hours and an increased risk of incident hypothyroidism with a dose-response relationship.
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Summary
Korean summary
대규모 코호트연구를 통해 장시간노동을 수행한 노동자들에서 갑상선기능저하증의 위험이 높아지는 것을 확인할 수 있었다. 특히 연령, 성, 교대근무 유무에 따라 층화하여 분석한 결과에서 고연령, 남성, 교대근무를 하지 않는 노동자에서 관련성의 크기가 증가하였다.
Key Message
This large-scale cohort study (The Kangbuk Samsung Health Study), which used 45,259 participants without thyroid disease at baseline and estimated hazard ratios (HRs) using Cox proportional hazards regression analysis, demonstrated the association between long working hours and an increased risk of incident hypothyroidism with a dose-response relationship especially in older age group, men, and daytime workers.
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Citations
Citations to this article as recorded by  - Association between shift work and the risk of hypothyroidism in adult male workers in Korea: a cohort study
Seonghyeon Kwon, Yesung Lee, Eunhye Seo, Daehoon Kim, Jaehong Lee, Youshik Jeong, Jihoon Kim, Jinsook Jeong, Woncheol Lee
Annals of Occupational and Environmental Medicine.2023;[Epub] CrossRef
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