The association between diabetes and thyroid cancer risk: a hospital-based case-control study in China.

Background: Previous studies have indicated inconsistent relationships of diabetes with thyroid cancer risk, yet little is known in China. In this study, we aimed to investigate the associations between diabetes, diabetes duration and the risk of thyroid cancer in Chinese population.

Methods: A 1:1 matched case-control study was performed between 2015 and 2017 in Zhejiang Province including 2,937 thyroid cancer cases and 2,937 healthy controls. Odds ratios (ORs) with 95 % confidence intervals (CIs) for thyroid cancer were estimated in logistic regression models. Specific effects stratified by age, as well as sex, body mass index (BMI) and family history of diabetes were also examined.

Results: Overall, neither diabetes (OR = 0.75, 95 % CI: 0.21-2.73) nor diabetes duration (OR = 0.14, 95 % CI: 0.02-1.22 for diabetes duration ≦ 5 years; OR = 2.10, 95 % CI: 0.32-13.94 for diabetes duration > 5 years) was significantly associated with thyroid cancer. In stratified analyses, significant lower risk of thyroid cancer was observed among subjects with diabetes and shorter diabetes duration ( ≦ 5 years), but limited to those who were aged more than 40 years, female, overweight/obese and had positive family history of diabetes.

Conclusions: Diabetes and shorter diabetes duration were significantly associated with decreased risk of thyroid cancer in individuals characterized by older age, female sex, higher BMI and positive family history of diabetes.