Shift work, sleep, and thyroid function in the National Health and Nutrition Examination Survey (2007-2012)

Abstract

Background Night shift work and poor sleep quality are associated with a wide range of chronic diseases, including thyroid disease. A limited number of studies have evaluated an association between night shift work and thyroid stimulating hormone (TSH) and an even fewer number of studies have evaluated an association between thyroid function and poor sleep quality or sleep duration. To examine possible links, this study examines five thyroid biomarkers: thyroid stimulating hormone (TSH) triiodothyronine (free T3 and total T3), thyroxine (free T4and total T4), thyroid peroxidase antibodies (TPO) and antithyroglobulin antibodies (ATG), and their association with night shift work, sleep duration and sleep problems.

Methods Data from the National Health and Nutrition Examination Survey (NHANES) from 2007 to 2012 was obtained from the Center for Disease Control and Prevention (CDC) website. Three cycles were combined to increase sample size. The relationship between night shift work and biomarker levels was analyzed using general linear regression models adjusted for a) age, b) ethnicity, gender and alcohol consumption. In addition, the association of sleep duration and quality and thyroid biomarkers was evaluated in age and multi-variable adjusted models and beta coefficients and 95% IC were reported.

Results The analytic sample comprised 4,095 participants from the United States. The main results show that evening workers have increased TSH (p<0.05) and ATG (p<0.05) and T3 (p<0.05) levels compared to daytime workers. However, no difference in the examined biomarkers was found between night shift and day workers (p>0.05). Thyroid levels did not show any significant difference (p>0.05) across sleep duration categories (<6 hours, 7 hours, >8 hours). Participants suffering from sleep problems experience decreased T3 (free and total) levels (p<0.05).

Conclusion

Overall, night shift work or sleep duration was not associated with altered thyroid biomarker levels. However, evening workers were at risk of higher thyroid biomarker levels, compared to day workers, and people with sleep problems had lower T3 levels than people who do not have sleep problems.