Background There are few studies on the diet quality of patients with thyroid cancer, and the relationship between diet quality and thyroid cancer remains uncertain. Objective This study aims to assess the diet quality with the Chinese Health Diet Index (CHDI) and to explore the relationship between diet quality and papillary thyroid carcinoma (PTC). Methods A 1∶1 gender- and age-matched hospital-based case-control study included newly diagnosed PTC patients and matched controls from Shanghai Cancer Hospital and Renji Hospital (East) in Shanghai, China. A structured questionnaire was applied to collect data on general characteristics, history of diseases, dietary intakes, and lifestyles. Food intakes in the past one year were assessed using a validated food frequency questionnaire, from which the CHDI score was calculated. The CHDI, according to the Dietary Guidelines for Chinese Residents, was employed to evaluate the diet quality of the two groups. A multiple conditional logistic regression model was conducted to explore the relationship between diet quality and PTC. Results A total of 350 pairs of cases and controls were recruited. The overall median CHDI score of the cases was lower than that of the controls (67.8 vs. 73.4, P<0.001). The cases had lower median scores of fruits (6.8 vs. 9.5), dairy products (3.6 vs. 5.6), and soybeans (4.6 vs. 5.5) than the controls (P<0.05); the cases had a higher median score of refined grains than the controls (5.0 vs. 4.9), and the percentage of the cases that met diet recommendations for refined grains was higher than the percentage of the controls (65.4% vs. 48.6%) (P<0.05); the cases showed lower median scores of whole grains/beans/tubers, total vegetables, dark vegetables, and fish/shrimps (0.9 vs. 1.4, 3.1 vs. 4.4, 3.6 vs. 5.0, and 3.3 vs. 4.0, respectively), and the percentages of the cases meeting their diet recommendations were lower than the percentages of the controls (6.3% vs. 8.6%, 32.6% vs. 42.0%, 38.6% vs. 50.6%, and 34.0% vs. 40.3%, respectively, P<0.05). The results of multiple conditional logistic regression analysis suggested that qualified and good diet quality were associated with a reduced the risk of PTC (qualified diet quality, OR=0.37, 95%CI: 0.23−0.62; good diet quality, OR=0.19, 95%CI: 0.10−0.36); the statistical significance remained after excluding patients who had a history of benign thyroid conditions (qualified diet quality, OR=0.28, 95%CI: 0.15−0.52; good diet quality, OR=0.20, 95%CI: 0.09−0.43). Conclusion Those with qualified or good diet quality have a lower risk of PTC. PTC patients have insufficient intakes of fruits, dairy, soybeans, whole grains/beans/tubers, vegetables, and fish/shrimps.

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.