Shift work has been reported to have several harmful effects on the human body. However, a small number of studies have evaluated the association between shift work and adverse effects on the thyroid. In our longitudinal study, we examined the causal association between shift work and the risk of hypothyroidism.
A Kangbuk Samsung Cohort Study was conducted on 112,648 men without thyroid disease at baseline who were followed up at least once between 2012 and 2019. Shift work status and shift schedule types were categorized using standardized questionnaires. Hypothyroidism was defined using the reference ranges of serum thyroid-stimulating hormones and free thyroxine levels. Hazard ratios (HRs) and 95% confidence intervals (CIs) for incident hypothyroidism were estimated using Cox proportional hazards regression analyses with the daytime work group as the reference.
During the 501,237 person-years of follow-up, there were 6,306 incident cases of hypothyroidism (incidence density, 1.26 per 100 person-years). The multivariable-adjusted HR of incident hypothyroidism for the shift work total group that included all shifts compared with the daytime work group was 1.27 (95% CI: 1.15–1.40). For the fixed evening, fixed night, rotating shift, and other shift workers, the multivariable-adjusted HRs (95% CI) were 1.11 (0.76–1.61), 2.18 (1.20–3.93), 1.39 (1.23–1.56), and 1.00 (0.82–1.22), respectively. In subgroup analyses by age, the association between shift work and hypothyroidism was more pronounced in younger participants (< 40 years; HR: 1.31; 95% CI: 1.16–1.47).
Our large-scale cohort study showed an association between shift work and the incidence of hypothyroidism, especially in younger workers with night shifts.
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Night shift work induces physiological and psychological stress by altering sleep and biological rhythms and is associated with hypertension, diabetes, obesity, and cardiovascular diseases. Few studies have been conducted on the control of hypertension and diabetes. This study aimed to examine the effect of night shift work on the control rate of hypertension and diabetes.
Subjects comprised workers aged 20–65 years who underwent specific health examination at a single facility in seven different affiliated examination centers from 1 January to 31 December 2016. Workers were categorised into day workers and night shift workers. Demographic and medical history were taken, and physical examination was done. Blood pressure (BP) and fasting glucose were measured. The control rate of each disease was evaluated based on treatment goals presented in the treatment guidelines of the Korean Society of Hypertension and the Korean Diabetes Association (systolic BP < 140 mmHg and diastolic BP < 90 mmHg; fasting glucose ≤ 130 mg/dL).
Among 631,418 subjects, 11.2% (70,450) were night shift workers. Of whom 6.1% (4,319) were taking antihypertensive medication and 2.5% (1,775) were taking diabetes medication. Among patients taking antihypertensive medications, the proportion of those whose BP was controlled to suit treatment goals was 81.7% (26,635) of day workers and 77.4% (3,343) of night shift workers, which was significantly different (
Night shift work can have an effect on the uncontrolled BP in workers taking antihypertensive medications. Therefore, additional efforts for disease control are necessary for night shift workers with hypertension.
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