Association between seafood intake and the risk of thyroid cancer.

Previous observational epidemiological studies such as case-control studies and cohort studies have reported inconsistent results regarding the associations between seafood intake and the risk of thyroid cancer. We searched PubMed and EMBASE in August 2021 using keywords related to seafood intake and thyroid cancer. A pooled odds ratio (OR) or relative risk (RR) with its 95% confidence interval (CI) was calculated. We included 17 observational studies with 13 case-control studies and 4 cohort studies, which included 4,309 thyroid cancer patients among 599,161 participants. In the random effects model meta-analysis of all 17 studies, we found that there was no significant association between seafood intake (highest vs. lowest intake) and the risk of thyroid cancer (OR or RR, 1.01; 95% CI: 0.86 to 1.19; I=51.4%). Although the associations were not statistically significant, subgroup meta-analyses by study design showed opposite findings: seafood intake decreased the risk of thyroid cancer in case-control studies (OR or RR, 0.94; 95% CI: 0.74 to 1.19; I=60.6%; n=13) but increased in cohort studies (OR or RR, 1.14; 95% CI: 0.97 to 1.35; I=0.0%; n=4). The current meta-analysis of observational epidemiological studies found that that overall, there was no significant association between seafood intake and the risk of thyroid cancer. However, given that cohort studies give us a higher level of evidence than case-control studies, further prospective cohort studies are warranted to confirm the association between them.