Thyroid cancer and Its Associations with Dietary Quality in A 1:1 matched Case-Control Study.

Thyroid cancer (TC) incidence has increased greatly during the past decades with a few established risk factors, while no study is available that has assessed the association of the Chinese Health Dietary Index (CHDI) with TC. We conducted a 1:1 matched case-control study in two hospitals in Shanghai, China. Diet quality scores were calculated according to CHDI using a validated and reliable food-frequency questionnaire. Conditional logistic regression analysis and Restricted cubic spline (RCS) analysis was used to reveal potential associations between CHDI score and thyroid cancer risk. A total of 414 pairs of historically confirmed TC patients and healthy controls were recruited from November 2012 to December 2015. The total score of cases and controls were 67.5 and 72.8, respectively (p < 0.001). The median score of total vegetables, fruit, diary, dark green and orange vegetables, fish, shellfish and mollusk, soybean, and whole grains, dry bean and tuber in cases was significantly lower than those in controls. Compared to the reference group (≤60 points), the average (60∼80 points) and high (≥80 points) levels of the CHDI score were associated with a reduced risk of TC (OR: 0.40, 95% Cl: 0.26∼0.63 for 60∼80 points; OR: 0.22, 95% Cl: 0.12∼0.38 for ≥80 points). In age-stratified analyses, the favorable association remained significant among participants who younger than 50 years old. Our data suggested that high diet quality as determined by CHDI was associated with lower risk of TC.