Smoking, alcohol consumption, and the risk of thyroid cancer

It is unclear if cigarette smoking and alcohol consumption are associated with thyroid cancer risk. A study with a Korean population explored associations between cigarette smoking and alcohol consumption with thyroid cancer.
Using data from the Korean National Health Insurance database, the study included individuals aged ≥20 years who participated in the 2009 health screening program and were followed until 2017. The risk of thyroid cancer was estimated, adjusted for age, sex, regular exercise, monthly income, body mass index, diabetes mellitus, and dyslipidemia.
During a mean follow-up period of 8.33 years, of 9,699,104 participants, 89,527 (0.9%) were diagnosed with thyroid cancer. Compared with those who never smoked, current smokers had a lower risk of thyroid cancer [aHR: 0.74, 95% confidence interval (CI): 0.72-0.76)], while ex-smokers did not (aHR: 0.98, 95% CI: 0.96-1.01). There was no significant dose-response relationship with regards to daily amount smoked, duration of smoking, or pack-years.
A reduced risk of thyroid cancer was observed in subjects who reporting the following categories of alcohol intake (compared to none): mild (aHR: 0.92, 95% CI: 0.90-0.93), moderate (aHR: 0.86, 95% CI: 0.84-0.89) and heavy (aHR: 0.86, 95% CI: 0.82-0.89). Inverse associations with thyroid cancer risk were observed regarding the number of drinking episodes per week and the number of drinks per occasion. A sub-multiplicative effect of smoking and alcohol consumption was observed.
The researchers observe that thyroid cancer risk was inversely associated (reduced) with smoking and alcohol consumption, with a significant interaction between these variables.
Source: Yeo Y, Shin DW, Han K, Kim D, Kim TH, Chun S, Jeong SM, Song YM. Smoking, alcohol consumption, and the risk of thyroid cancer: a population-based Korean cohort study of 10 million people. Thyroid. 2022 Mar 2. doi.org/10.1089/thy.2021.0675.