Iodine excess has been suggested as an exogenous risk factor of papillary thyroid cancer (PTC). We performed a systematic review and meta-analysis to assess the relationship between iodine exposure measured in various forms and PTC prevalence.

We searched MEDLINE, Embase, and the Cochrane Library for case-control studies on iodine and PTC published up to December 2015. Exposure to iodine was compared between PTC and control groups.

From the 16 selected studies, the odds ratio (OR) for the overall effect size between high iodine exposure and PTC risk was 1.418 (95% confidence interval [CI] 1.054-1.909). Based on 7 studies conducted in high iodinated regions, a positive association between iodine exposure and PTC was observed (OR 2.200; 95% CI 1.389-3.483).

This study demonstrated a higher exposure to iodine in patients with PTC compared with controls, especially for patients from high iodinated regions.