March 24, 2020
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Smoking, daily drinking associated with lower thyroid cancer risk

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Yohwan Yeo
Dong Wook Shin

Korean adults who reported being daily smokers and drinkers were less likely to develop thyroid cancer during 5 years of follow-up compared with never-smokers and never-drinkers, according to findings published in Thyroid.

“The association between smoking, alcohol consumption and thyroid cancer has been evaluated in previous studies, yet the results remain controversial,” Dong Wook Shin, MD, DrPH, MBA, professor in the department of digital health at Sungkyunkwan University in Seoul, South Korea, told Healio. “In this very large study, we found that smoking and drinking was associated with reduced risk for thyroid cancer. As this study is epidemiological, we do not know exact mechanism for such associations. Previous studies suggested several mechanisms, the most probable being a decrease of thyroid-stimulating hormone by smoking and alcohol consumption.”

Smoking, lower risk

Shin and colleagues analyzed data from 22,809,391 adults aged at least 20 years between 2009 and 2012, using data from Korean National Health Insurance database, a populationbased longitudinal cohort study. Researchers used Cox proportional hazard models to estimate the adjusted HR for risk for thyroid cancer, adjusted for age, sex, physical activity, monthly income, BMI and diabetes status.

During a mean followup of 5.36 years, 174,247 adults (0.8%) were diagnosed with thyroid cancer.

Yeo Graphic
The rate of thyroid cancer development among Korean adults who were daily smokers and drinkers during a 5-year followup was lower compared with never-smokers and never-drinkers.

Compared with current smokers, neversmokers were 34% more likely to develop thyroid cancer (adjusted HR = 1.34; 95% CI, 1.32-1.37); past smokers were similarly 35% more likely to develop thyroid cancer during follow-up (aHR = 1.35; 95% CI, 1.32-1.38).

The researchers did not observe a doseresponse relationship when stratifying adults by daily amount of smoking, duration of smoking, and packyears.

Effect of alcohol intake

The researchers also observed a decrease in thyroid cancer risk among adults who reported daily alcohol consumption. Compared with nondrinkers, those who reported consuming seven drinks per week were 22% less likely to develop thyroid cancer during follow-up (aHR = 0.78; 95% CI, 0.73-0.83), whereas adults who reported consuming at least 15 g per occasion were 14% less likely to develop thyroid cancer (aHR = 0.86; 95% CI, 0.82-0.9).

Compared with heavy drinkers, so-called mild drinkers (< 15 g per day) were 7% more likely to develop thyroid cancer (aHR = 1.07; 95% CI, 1.04-1.1) and never-drinkers were 16% more likely to develop thyroid cancer (aHR = 1.16; 95% CI, 1.12-1.19).

The researchers noted that there was an interaction between smoking and drinking on thyroid cancer risk (P < .0001), adding that the risk for thyroid cancer among nonsmokers and never-drinkers (aHR = 1.58; 95% CI, 1.51-1.65) was higher than what was expected due to independent effects of nonsmoking and nondrinking (aHR = 1.46).

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The effect of smoking was more pronounced among younger people, whereas the effect of alcohol consumption was more pronounced among older adults and women, according to the researchers.

“The results of this study should be interpreted carefully,” Shin said. “While our study suggests reduced risk for thyroid cancer by smoking and drinking, it is a scientific one. Overall health risk increased by smoking and alcohol consumption far outweigh the benefit from reduced thyroid cancer risk. Studies to elucidate how smoking and alcohol consumption are related to the pathogenesis of thyroid cancer development are needed.” – by Regina Schaffer

For more information:

Dong Wook Shin, MD, DrPH, MBA, can be reached at the Department of Digital Health, SAIHST, Sungkyunkwan University, 81 Irwon-Ro, Gangnam-gu, Seoul 06351, South Korea; email: dwshin.md@gmail.com.

Disclosures: The authors report no relevant financial disclosures.