Dietary Factors Affecting Thyroid Cancer Risk: A Meta-Analysis.

Some dietary factors are proposed to affect thyroid carcinogenesis, but previous studies have reported inconsistent findings. Therefore, we performed a meta-analysis, including 18 eligible studies, to clarify the role of dietary factors in the risk of thyroid cancer. The relative risks (RRs) with 95% confidence intervals (95% CIs) were estimated to assess the association and heterogeneity tests and subgroup and sensitivity analyses, and bias assessments were performed. When the results from all studies were combined, dietary iodine, fish, and cruciferous vegetable intake were not associated with thyroid cancer. However, when the data were divided by geographic location based on iodine availability, a slight increase in the risk of thyroid cancer was observed among those consuming a high total amount of fish in iodine nondeficient areas (RR: 1.18; 95% CI: 1.03-1.35; P for heterogeneity = 0.282). When excluding the studies examining a single food item and hospital-based controls, a high intake of cruciferous vegetables was associated with an increased risk of thyroid cancer in iodine-deficient areas (RR: 1.43; 95% CI: 1.18-1.74; P for heterogeneity = 0.426). This meta-analysis implies that the role of dietary factors, such as fish and cruciferous vegetables, in thyroid cancer risk can differ based on iodine availability.