Alcohol Intake and Risk of Thyroid Cancer: A Meta-Analysis of Observational Studies

Seung-Hee Hong, Seung-Kwon Myung, Hyeon Suk Kim

To assess whether alcohol intake is associated with the risk of thyroid cancer by meta-analysis of observational studies. We searched PubMed and EMBASE in June of 2015 to locate eligible studies. We included observational studies such as cross-sectional studies, case-control studies, and cohort studies reporting odd ratios (ORs) or relative ratios (RRs) with 95% confidence intervals (CIs). We included 33 observational studies with two cross-sectional studies, 20 case-controls studies, and 11 cohort studies, which involved a total of 7,725 thyroid cancer patients and 3,113,679 participants without thyroid cancer in the final analysis. In the fixed-effect model meta-analysis of all 33 studies, we found that alcohol intake was consistently associated with a decreased risk of thyroid cancer (odds ratio or relative risk 0.74, 95% confidence interval 0.67 to 0.83; I2 = 38.6%). In the subgroup meta-analysis by type of study, alcohol intake also decreased the risk of thyroid cancer in both case-control studies (odds ratio 0.77, 95% confidence interval 0.65 to 0.92; I2 = 29.5%; n =20) and cohort studies (relative risk 0.70, 95% confidence interval 0.60 to 0.82; I2 = 0%; n = 11). Moreover, subgroup meta-analyses by type of thyroid cancer, gender, amount of alcohol consumed, and methodological quality of study showed that alcohol intake was significantly associated with a decreased risk of thyroid cancer. The current meta-analysis of observational studies found that, unlike most of other types of cancer, alcohol intake decreased the risk of thyroid cancer.