Researchers used information from the Korean National Health Insurance database to identify patients aged ≥20 years who participated in health screening program in 2009. These patients (n=9,699,104) were followed until 2017. Researchers estimated thyroid cancer risk adjusted for age, sex, physical activity, monthly income, body mass index, and diabetes status.
Smoking and drinking associated with reduced risk of thyroid cancer
After a mean follow-up of 8.33 years, 89,527 patients (0.9%) were diagnosed with thyroid cancer. Compared with smokers, those who had never smoked had a 34% increased risk of thyroid cancer (adjusted hazard ratio [HR], 1.34; 95% CI, 1.32-1.37). Former smokers were also 35% more likely to develop thyroid cancer than current smokers (adjusted HR, 1.35; 95% CI, 1.32-1.38). There did not appear to be a dose-response relationship with regard to the daily amount of smoking, duration of smoking, and pack-years.
Compared with those who did not drink, patients who reported consuming seven drinks per week were 22% less likely to develop thyroid cancer (adjusted HR, 0.78; 95% CI, 0.73-0.83). Those who reported consuming at least 15 g per occasion were 14% less likely to develop thyroid cancer (adjusted HR, 0.86; 95% CI, 0.82-0.9).
A certain degree of alcohol consumption appeared to show a decreased risk of thyroid cancer compared with those who did not drink (HR, 0.85; 95% CI, 0.81-0.89 for ≥40 g/week).
The interaction of smoking and alcohol consumption was significant (P<0.0001), according to the authors.
“Further studies are needed to elucidate exactly how smoking and alcohol are related to the pathogenesis and the modification their effects may have on thyroid cancer development,” the researchers noted.