The relationship between night shift-work and thyroid nodule: a field study among the employees of Yazd Electricity Company.

Background: Night work includes working between 10 pm and 6 am, which has known effects on people's health. One of the hormones influenced by the circadian rhythm is thyroid stimulating hormone (TSH).

Objective: Considering the effects of night shift-work on the thyroid gland, the purpose of this study was to investigate the relationship between thyroid nodules and night shift-work among the employees of Yazd Electricity Company.

Methods: This was a cross-sectional study on employees of Yazd Electricity Company. Demographic information including age, gender, level of education, smoking, work experience and shift- work was recorded and blood pressure, height and weight of the subjects were measured. Thyroid sonography was performed for the subjects. The frequency of thyroid nodules in each group of night shift and non-night shift work groups was determined and compared.

Results: Among 433 participants, 47 people (10.9%) were night shift-workers and 386 people (89.1%) were non-night shift-workers. The frequency of thyroid nodule was 12.8% among night shift-workers and 18.1% among non-night shift-workers, and no significant correlation was seen between two groups (P = 0.438). Also, the frequency of thyroid nodule was not significantly different between two groups in terms of smoking, gender and work experience. Uni-variate and multi-variate logistic regression model showed that old age and high BMI increased the probability of abnormal thyroid sonographic findings by 6% and 8%, respectively.

Conclusions: There was no relationship between night shift-work and the frequency of thyroid nodule.