Metabolic Disease and Risk of Thyroid Disease: Evidence from the National Nurse Health Cohort in China.

Background: Previous studies have shown that metabolic diseases are risk factors for thyroid disease; most studies are cross-sectional design. We aimed to evaluate the causal relationship between thyroid and metabolic diseases in a cohort of Chinese nurses.

Methods: We conducted an ambispective cohort study of the National Nurses' Health Study. Thyroid disease data based on ultrasonography from 2017 to 2021 were collected. We described thyroid disease incidence and the risk factors associated with a cluster of metabolic factors. We used the Mann‒Whitney U test, repeated-measures ANOVA and multivariable Cox proportional hazard regression to analyze the data.

Results: A total of 1529 female nurses without thyroid disease were enrolled in 2017, of which, complete data were available for 1269 nurses. In 2018-2020, thyroid nodule incidence ranged from 32.8%-46.3%, thyroiditis incidence was 13.4%-14.3%, and goiter incidence was 4.1%-29.1%, thyroid adenoma and thyroid tumors incidence were 0.1%-0.5% and 1%-1.5%. We also found that NAFLAD was an independent risk factor for thyroid adenoma (p = .003). The age at diagnosis was an independent risk factor for goiter (p <. 001) and thyroid nodules (p < .001). Fasting blood glucose was an independent risk factor for thyroid tumors (p = .004). The age at diagnosis (p = .003), Body Mass Index (p = .006) and menopause (p = .031) were risk factors for thyroiditis.

Conclusion: Thyroid disease incidence among nurses is increasing. Age at diagnosis, BMI, fasting blood glucose, and nonalcoholic fatty liver disease are independent risk factors for different types of thyroid disease. This study provides evidence for future studies to further explore the pathogenesis and prevention of thyroid diseases.