Background  Thyroid carcinoma is a serious threat to human health in Shanghai and a focus of cancer prevention and treatment.

Objective  This study aims to assess the relationship between foods rich in iodine and papillary thyroid carcinoma (PTC)．

Methods  In a hospital-based case-control study matched by gender and age (±3 years old), 402 pairs of cases (new incidences) and controls were included and studied. A validated questionnaire and food frequency questionnaire survey was conducted face to face to obtain demographic characteristics and dietary intake. A multiple conditional logistic regression model was applied to explore the relationship between foods rich in iodine (including seaweeds, kelp, and dried shrimps) and PTC.

Results  The mean age of the participants was (41.17±11.51) years in this study. Compared with the controls, more cases had a lower education and a manual occupation (P<0.05); more cases were overweight or obese, had a history of benign thyroid conditions, and had a family history of thyroid diseases (P<0.05); the two groups were different in the frequency of CT examination in the past ten years (P<0.05). The results of multiple conditional logistic regression analysis showed that consumption of iodine-rich foods was associated with a lower risk of PTC (for <1 time per week,OR=0.20, 95%CI: 0.12−0.35; for 1−2 times per week, OR=0.18, 95%CI: 0.10−0.33; for ≥3 times per week, OR=0.13, 95%CI: 0.04−0.44) (P<0.05). Specifically, those who consumed seaweeds (for <1 time per week,OR=0.18, 95%CI: 0.11−0.30; for 1−2 times per week, OR=0.11, 95%CI: 0.05−0.23; for ≥3 times per week, OR=0.15, 95%CI: 0.03−0.75), kelp (for <1 time per week, OR=0.28, 95%CI: 0.18−0.43; for ≤2 times per week, OR=0.24, 95%CI: 0.11−0.50), and dried shrimps (for <1 time per week, OR=0.44, 95%CI: 0.29−0.69; for ≤2 times per week: OR=0.34, 95%CI: 0.18−0.65) had a lower risk of PTC (P<0.05). After excluding patients who had a history of benign thyroid conditions, the favorable association remained significant among patients who had consumption of iodine-rich foods, seaweeds, shrimps, and kelp (P<0.05).

Conclusion  Less PTC patients consume iodine-rich foods than the controls.